1 00:00:00,500 --> 00:00:02,830 The following content is provided under a Creative 2 00:00:02,830 --> 00:00:04,370 Commons license. 3 00:00:04,370 --> 00:00:06,670 Your support will help MIT OpenCourseWare 4 00:00:06,670 --> 00:00:11,030 continue to offer high quality educational resources for free. 5 00:00:11,030 --> 00:00:13,660 To make a donation or view additional materials 6 00:00:13,660 --> 00:00:17,610 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,610 --> 00:00:18,540 at ocw.mit.edu. 8 00:00:26,440 --> 00:00:28,490 JOANNE STUBBE: At the end of the last lecture, 9 00:00:28,490 --> 00:00:33,310 we were talking about some generic properties of metals. 10 00:00:33,310 --> 00:00:38,680 And we were talking about the Irving-Williams series that 11 00:00:38,680 --> 00:00:44,020 was talked about, and will talk about in recitation this week, 12 00:00:44,020 --> 00:00:48,520 and this issue of how do you control metalation 13 00:00:48,520 --> 00:00:53,350 inside the cells when inherently copper is going to bind more 14 00:00:53,350 --> 00:00:55,840 tightly than zinc. 15 00:00:55,840 --> 00:01:01,210 And so if you have same amounts in solution, 16 00:01:01,210 --> 00:01:04,870 copper is always going to win, even though it clearly 17 00:01:04,870 --> 00:01:09,040 is dependent on the environment, the ligands, et cetera, which 18 00:01:09,040 --> 00:01:09,940 we didn't talk about. 19 00:01:09,940 --> 00:01:18,070 So the Irving-Williams series is an overview based on binding. 20 00:01:18,070 --> 00:01:21,850 Without that much details, it assumes octahedral environment 21 00:01:21,850 --> 00:01:26,020 plus 2 oxidation state, and it gives you an intuitive feeling 22 00:01:26,020 --> 00:01:27,570 for what the binding might be. 23 00:01:27,570 --> 00:01:32,320 And we focused on one creative solution 24 00:01:32,320 --> 00:01:36,160 that is controlling the location of the folding, 25 00:01:36,160 --> 00:01:39,340 so that you could pick up the appropriate metal 26 00:01:39,340 --> 00:01:40,930 and get correct metalation. 27 00:01:40,930 --> 00:01:46,330 In this case, on the cyanobacteria 28 00:01:46,330 --> 00:01:48,970 that they looked at in the periplasm, 29 00:01:48,970 --> 00:01:51,760 they have two proteins that have the same structures, virtually 30 00:01:51,760 --> 00:01:54,040 the same ligand spheres. 31 00:01:54,040 --> 00:01:57,520 Yet, they're able to selectively metalate. 32 00:01:57,520 --> 00:02:02,140 So and there are a few more things 33 00:02:02,140 --> 00:02:04,840 I want to mention about metals, in general. 34 00:02:04,840 --> 00:02:09,700 And the third thing is tuning metals. 35 00:02:17,540 --> 00:02:21,230 And the things that are going to tune the metals, 36 00:02:21,230 --> 00:02:23,840 we'll see when we look at iron specifically, 37 00:02:23,840 --> 00:02:29,120 but this is true of all metals, is the ligands, so 38 00:02:29,120 --> 00:02:39,670 the first coordination sphere, the geometry around the metals. 39 00:02:39,670 --> 00:02:44,728 So in the cases we were looking at the last time, 40 00:02:44,728 --> 00:02:46,270 with the Irving-Williams series, they 41 00:02:46,270 --> 00:02:48,760 were looking at an octahedral environment, but most of you 42 00:02:48,760 --> 00:02:50,800 know you can have tetrahedral environments, 43 00:02:50,800 --> 00:02:53,080 trigonal bipyramidal. 44 00:02:53,080 --> 00:02:54,940 You can have square planar. 45 00:02:54,940 --> 00:02:56,453 There are all kinds of environments, 46 00:02:56,453 --> 00:02:58,120 so you need to think about the geometry. 47 00:03:01,810 --> 00:03:04,300 We'll see later on, with transition metals, 48 00:03:04,300 --> 00:03:06,670 we need to look at the spin states. 49 00:03:06,670 --> 00:03:10,060 It can control the oxidation and reduction. 50 00:03:10,060 --> 00:03:19,900 So we'll look at spin state oxidation and reduction. 51 00:03:19,900 --> 00:03:22,360 And we need to also think about-- 52 00:03:22,360 --> 00:03:25,810 and this is something that a lot of chemists 53 00:03:25,810 --> 00:03:28,960 are now finally trying to build into their molecules-- 54 00:03:28,960 --> 00:03:33,970 it's not just the immediate environment around the metals, 55 00:03:33,970 --> 00:03:37,488 but the second coordination sphere. 56 00:03:37,488 --> 00:03:40,030 And this is hard to build in, from a chemist's point of view. 57 00:03:40,030 --> 00:03:46,480 It's not so hard to tune in from a protein 58 00:03:46,480 --> 00:03:50,620 environmental approach because you could have hydrogen bonding 59 00:03:50,620 --> 00:03:53,020 to an oxygen, which could then tweak 60 00:03:53,020 --> 00:03:56,710 the PKA of the ligand bound to the metal. 61 00:03:56,710 --> 00:04:03,490 So why do you have such a big protein? 62 00:04:03,490 --> 00:04:07,510 And why can't chemists recapitulate rate accelerations 63 00:04:07,510 --> 00:04:11,240 that are actually observed in enzymes? 64 00:04:11,240 --> 00:04:13,630 And it's simply because you need the whole protein. 65 00:04:13,630 --> 00:04:16,630 So it really is not just the first coordination sphere 66 00:04:16,630 --> 00:04:18,250 and the second. 67 00:04:18,250 --> 00:04:22,000 You can make mutations far removed from the active site, 68 00:04:22,000 --> 00:04:24,463 and actually affect, in this case, 69 00:04:24,463 --> 00:04:26,380 the properties of the metal, or the properties 70 00:04:26,380 --> 00:04:30,250 of whatever groups are actually involved in catalysis. 71 00:04:30,250 --> 00:04:33,760 And this is an example I took out 72 00:04:33,760 --> 00:04:36,650 of their very recent literature which I think is quite amazing. 73 00:04:36,650 --> 00:04:40,390 And I also think it's indicative of where chemistry 74 00:04:40,390 --> 00:04:47,170 is going in the next five years in the organometallic area. 75 00:04:47,170 --> 00:04:51,630 So this is a paper that was published by Yi Lu, who's 76 00:04:51,630 --> 00:04:54,010 at the University of Illinois. 77 00:04:54,010 --> 00:04:58,260 And what he was trying to do is he took a small little protein. 78 00:04:58,260 --> 00:05:00,850 The protein happens to be azurin that binds copper. 79 00:05:00,850 --> 00:05:03,550 It really doesn't matter what the protein is. 80 00:05:03,550 --> 00:05:07,390 But it does oxidation and reduction of copper. 81 00:05:07,390 --> 00:05:13,930 And what he was able to do is by changing the metal-- 82 00:05:13,930 --> 00:05:17,340 so he could either use copper or he could use nickel. 83 00:05:17,340 --> 00:05:21,130 And by changing the first and second coordination sphere 84 00:05:21,130 --> 00:05:24,550 around the metal by site-directed mutagenesis-- 85 00:05:24,550 --> 00:05:27,820 and at most, he made five mutants-- 86 00:05:27,820 --> 00:05:31,750 what he was able to do is tune the redox potential 87 00:05:31,750 --> 00:05:34,420 over 2 volts. 88 00:05:34,420 --> 00:05:37,540 So that is pretty astonishing, I think. 89 00:05:37,540 --> 00:05:40,010 And so he has structures. 90 00:05:40,010 --> 00:05:42,700 Here's a thing with two histidines and a methionine. 91 00:05:42,700 --> 00:05:46,090 He has structures of all of these species. 92 00:05:46,090 --> 00:05:49,030 And we would love to be able to put something-- chemists would 93 00:05:49,030 --> 00:05:54,010 love to be able to put things other than copper, or iron, 94 00:05:54,010 --> 00:05:56,590 or transition metals into proteins 95 00:05:56,590 --> 00:05:59,260 and control the redox potentials. 96 00:05:59,260 --> 00:06:03,170 And I think this is just the tip of the iceberg. 97 00:06:03,170 --> 00:06:05,860 I think this is an incredibly exciting result. 98 00:06:05,860 --> 00:06:10,360 And it also just allows me to show you 99 00:06:10,360 --> 00:06:14,080 that we've talked a little bit about iron sulfur cluster 100 00:06:14,080 --> 00:06:18,130 proteins, and we talked about that last time. 101 00:06:18,130 --> 00:06:24,850 We can go over 1.2 volts by changing the environment 102 00:06:24,850 --> 00:06:26,750 of the iron sulfur cluster. 103 00:06:26,750 --> 00:06:29,530 So you saw there were a number of flavors of iron sulfur 104 00:06:29,530 --> 00:06:33,820 clusters, and they all look pretty similar. 105 00:06:33,820 --> 00:06:36,790 But it's the protein in the environment that's tuning that. 106 00:06:36,790 --> 00:06:39,010 And the question that chemists are asking 107 00:06:39,010 --> 00:06:41,080 is, what are the basic principles 108 00:06:41,080 --> 00:06:44,470 that govern redox chemistry? 109 00:06:44,470 --> 00:06:49,000 Instead of having to select for something to change the redox 110 00:06:49,000 --> 00:06:52,960 potential, can we eventually go in and just 111 00:06:52,960 --> 00:06:54,110 rationally make a change? 112 00:06:54,110 --> 00:06:55,960 Especially now since you all know 113 00:06:55,960 --> 00:06:57,850 we can put in a natural amino acid. 114 00:06:57,850 --> 00:07:01,970 So we can put in ligands that aren't the normal repertoire 115 00:07:01,970 --> 00:07:02,470 for protein. 116 00:07:02,470 --> 00:07:06,580 So I think this is an incredibly exciting time 117 00:07:06,580 --> 00:07:09,970 because metal-based reactions offer 118 00:07:09,970 --> 00:07:11,710 huge numbers of opportunities. 119 00:07:11,710 --> 00:07:13,210 And I think we aren't going to be 120 00:07:13,210 --> 00:07:19,420 limited to the repertoire observed in biology. 121 00:07:19,420 --> 00:07:23,920 So and the last thing I wanted to talk about, 122 00:07:23,920 --> 00:07:29,200 in terms of generic systems, is that we had a cartoon 123 00:07:29,200 --> 00:07:32,440 and you looked a little bit at the diversity 124 00:07:32,440 --> 00:07:34,760 of metallocofactors. 125 00:07:34,760 --> 00:07:36,740 So we have a huge diversity. 126 00:07:36,740 --> 00:07:39,290 Where does the diversity come from? 127 00:07:39,290 --> 00:07:48,350 And in general in biology, there are biosynthetic pathways 128 00:07:48,350 --> 00:07:53,030 to make the metallocofactors. 129 00:07:55,580 --> 00:07:59,400 Also the organic cofactors, as well. 130 00:07:59,400 --> 00:08:05,810 So even something much simpler than the cofactor we looked 131 00:08:05,810 --> 00:08:11,390 at that converts nitrogen gas into ammonia-- remember, 132 00:08:11,390 --> 00:08:14,420 that had a lot of iron sulfurs and a molybdenum, 133 00:08:14,420 --> 00:08:18,530 and a carbide in the middle, and a citrate on one end. 134 00:08:18,530 --> 00:08:20,120 Very complex. 135 00:08:20,120 --> 00:08:22,790 Even in some of the simpler systems, 136 00:08:22,790 --> 00:08:27,710 it's likely there are going to be biosynthetic pathways 137 00:08:27,710 --> 00:08:29,510 to control all of this. 138 00:08:29,510 --> 00:08:33,679 And we're going to be focusing on, 139 00:08:33,679 --> 00:08:36,470 starting in today's lecture-- 140 00:08:36,470 --> 00:08:41,539 and the reason that I focused mostly thus far on iron sulfur 141 00:08:41,539 --> 00:08:46,580 clusters is we're going to see a major regulator of iron 142 00:08:46,580 --> 00:08:50,030 at the translational level are iron sulfur clusters. 143 00:08:50,030 --> 00:08:54,020 So I think looking at an iron sulfur cluster 144 00:08:54,020 --> 00:08:59,180 allows you to then maybe think about-- 145 00:08:59,180 --> 00:09:02,220 I think people don't think very much about this. 146 00:09:02,220 --> 00:09:06,210 What do you need to actually make one of these clusters? 147 00:09:06,210 --> 00:09:08,540 So this is a four iron, four sulfur cluster. 148 00:09:13,710 --> 00:09:14,680 Let's see. 149 00:09:14,680 --> 00:09:16,690 I got to put this up here a little bit more. 150 00:09:16,690 --> 00:09:20,280 So we have a cubane structure. 151 00:09:20,280 --> 00:09:24,940 And these are attached to proteins 152 00:09:24,940 --> 00:09:28,110 through-- irons are attached to the proteins through systanes. 153 00:09:30,890 --> 00:09:31,980 And this one is attached-- 154 00:09:31,980 --> 00:09:33,430 I'll draw it out here-- 155 00:09:33,430 --> 00:09:34,960 through a systane. 156 00:09:34,960 --> 00:09:38,740 And in many of the clusters now where chemistry happens, 157 00:09:38,740 --> 00:09:40,780 you're going to have binding through systanes. 158 00:09:40,780 --> 00:09:42,910 So each one of these guys is a systane. 159 00:09:45,520 --> 00:09:50,020 But you also have an iron that's not coordinated to a systane. 160 00:09:50,020 --> 00:09:51,550 So here you have any unique iron, 161 00:09:51,550 --> 00:09:53,950 and that is going to be key. 162 00:10:00,610 --> 00:10:03,910 This is iron. 163 00:10:03,910 --> 00:10:08,170 One of the first systems that people looked at involved-- 164 00:10:08,170 --> 00:10:11,140 maybe you remember back to the TCA cycle-- 165 00:10:11,140 --> 00:10:13,840 is a cytosolic aconitase. 166 00:10:13,840 --> 00:10:17,140 And people had really thought about iron sulfur clusters 167 00:10:17,140 --> 00:10:20,860 as only being involved in oxidation and reduction. 168 00:10:20,860 --> 00:10:23,350 And this one was the first example 169 00:10:23,350 --> 00:10:24,700 where citrate could bind here. 170 00:10:24,700 --> 00:10:27,190 So you had a unique iron allowing you to do chemistry. 171 00:10:27,190 --> 00:10:31,210 And now we know there are 100,000 types 172 00:10:31,210 --> 00:10:35,470 of enzymatic reactions that use iron sulfur clusters. 173 00:10:35,470 --> 00:10:37,600 So there's a couple of points I want 174 00:10:37,600 --> 00:10:39,430 to make because I think it's confusing, 175 00:10:39,430 --> 00:10:44,890 and we're going to use this when we think about the regulation. 176 00:10:44,890 --> 00:10:52,900 People write the oxidation species as plus 1 or plus 2. 177 00:10:52,900 --> 00:10:57,510 That's a typical oxidation of the iron sulfur clusters 178 00:10:57,510 --> 00:11:00,530 that we'll be dealing with. 179 00:11:00,530 --> 00:11:03,700 And so the question is, where does that number come from? 180 00:11:03,700 --> 00:11:07,510 And so what they do is ignore the cysteines. 181 00:11:07,510 --> 00:11:10,720 And so what you have is you have four sulfides, 182 00:11:10,720 --> 00:11:11,830 if I've drawn this right. 183 00:11:11,830 --> 00:11:13,690 One, two, three, four. 184 00:11:13,690 --> 00:11:18,370 So you have four sulfides, so that gives you a minus 8. 185 00:11:18,370 --> 00:11:20,260 And so then what does that tell you? 186 00:11:20,260 --> 00:11:21,970 You ignore the cysteines altogether. 187 00:11:21,970 --> 00:11:23,650 Then what does that tell you? 188 00:11:23,650 --> 00:11:26,080 To get a plus 2 state, what does that 189 00:11:26,080 --> 00:11:29,080 tell you about the oxidation state of the irons? 190 00:11:31,600 --> 00:11:35,650 So if we need a plus 2, what are the two common oxidation states 191 00:11:35,650 --> 00:11:36,645 of iron? 192 00:11:36,645 --> 00:11:37,920 AUDIENCE: Plus 2, plus 3. 193 00:11:37,920 --> 00:11:39,580 JOANNE STUBBE: Plus 2 and plus 3. 194 00:11:39,580 --> 00:11:43,090 So if we have plus 3 plus 3 plus 2 plus 2, 195 00:11:43,090 --> 00:11:47,950 that gives you plus 10, and that gives you the plus 2 oxidation. 196 00:11:47,950 --> 00:11:50,800 People get confused by that is the only reason I'm 197 00:11:50,800 --> 00:11:51,620 going through that. 198 00:11:51,620 --> 00:11:55,870 So if we want an overall plus 2, then you 199 00:11:55,870 --> 00:12:04,180 can have two iron 3s and two iron 2s. 200 00:12:04,180 --> 00:12:08,820 Now, it's not as simple as that because in some cases, 201 00:12:08,820 --> 00:12:13,150 the electrons can be delocalized, 202 00:12:13,150 --> 00:12:14,680 so you have 2 and 1/2 states. 203 00:12:14,680 --> 00:12:15,892 They're moving around a lot. 204 00:12:15,892 --> 00:12:18,100 And we're not going to talk about anything like that. 205 00:12:18,100 --> 00:12:20,170 You need to take bio and organic chemistry if you 206 00:12:20,170 --> 00:12:21,820 want to think about that. 207 00:12:21,820 --> 00:12:25,870 So if you look at this complex, you have a cube. 208 00:12:25,870 --> 00:12:28,030 It's got irons and it's got sulfides. 209 00:12:28,030 --> 00:12:30,460 That's it. 210 00:12:30,460 --> 00:12:34,015 What do you need to make something like this? 211 00:12:34,015 --> 00:12:35,140 What do you think you need? 212 00:12:41,550 --> 00:12:43,510 And this is true of all these cofactors. 213 00:12:43,510 --> 00:12:44,620 It's not just this one. 214 00:12:44,620 --> 00:12:47,330 This is the one we're going to actually worry about 215 00:12:47,330 --> 00:12:52,340 by the end of this lecture or the beginning of next lecture. 216 00:12:52,340 --> 00:12:54,830 Where does the iron come from? 217 00:12:54,830 --> 00:12:57,100 So you need something that can deliver the iron. 218 00:12:57,100 --> 00:12:59,480 Do you want iron 2 sitting around? 219 00:12:59,480 --> 00:13:03,020 We're going to talk about that more in module seven, 220 00:13:03,020 --> 00:13:06,860 but no, because iron 2 can undergo redox chemistry. 221 00:13:06,860 --> 00:13:13,430 So you need to deliver iron. 222 00:13:13,430 --> 00:13:15,260 What about the redox state of the irons? 223 00:13:18,160 --> 00:13:21,730 So I just told you they can be plus 2 or plus 3. 224 00:13:21,730 --> 00:13:22,890 How do you get that? 225 00:13:22,890 --> 00:13:25,270 How would you deliver the iron in the first place, 226 00:13:25,270 --> 00:13:28,880 given one of the rules we've already talked about? 227 00:13:28,880 --> 00:13:30,670 So you have iron inside the cell. 228 00:13:30,670 --> 00:13:32,110 Would you want it to be delivered 229 00:13:32,110 --> 00:13:35,410 in the plus 2 or the plus 3 state 230 00:13:35,410 --> 00:13:38,720 to a protein with no metal in it? 231 00:13:38,720 --> 00:13:40,360 AUDIENCE: Plus 3. 232 00:13:40,360 --> 00:13:41,110 JOANNE STUBBE: OK. 233 00:13:41,110 --> 00:13:42,220 Everybody agree with that? 234 00:13:45,640 --> 00:13:48,070 See, why do you say plus 3? 235 00:13:48,070 --> 00:13:51,054 AUDIENCE: Well, just because it won't undergo redox chemistry 236 00:13:51,054 --> 00:13:51,918 with the proteins. 237 00:13:51,918 --> 00:13:53,480 But I guess it is also insoluble, 238 00:13:53,480 --> 00:13:55,183 so then you have a problem of how 239 00:13:55,183 --> 00:13:56,950 do you go about delivering Fe 3 plus? 240 00:13:56,950 --> 00:13:59,033 JOANNE STUBBE: So you have, how do you deliver it. 241 00:13:59,033 --> 00:14:00,952 But you also have an additional factor, 242 00:14:00,952 --> 00:14:02,410 which you have to pay attention to, 243 00:14:02,410 --> 00:14:05,140 is the exchange rates of the ligands. 244 00:14:05,140 --> 00:14:09,370 So wherever it starts, it's got ligands on it, 245 00:14:09,370 --> 00:14:11,990 whether it's a protein or whether it's something else. 246 00:14:11,990 --> 00:14:15,550 And you have to go some kind of mechanism, associative 247 00:14:15,550 --> 00:14:18,460 or dissociative, to do exchange into the metals. 248 00:14:18,460 --> 00:14:21,340 So in general, we'll see one of the rules 249 00:14:21,340 --> 00:14:27,340 is that it's almost always iron 2 that's delivered. 250 00:14:27,340 --> 00:14:33,310 And so we need to control the redox state. 251 00:14:33,310 --> 00:14:37,990 And we'll see this big time when we look at humans, 252 00:14:37,990 --> 00:14:41,140 and how does iron get into cells. 253 00:14:41,140 --> 00:14:45,630 You've got toggle between plus 2 and plus 3 all of the time. 254 00:14:45,630 --> 00:14:52,420 And part of the rationale is related to ligand exchange. 255 00:14:52,420 --> 00:14:54,220 What else do we need to deliver? 256 00:14:54,220 --> 00:14:56,050 We need to deliver sulfide. 257 00:14:56,050 --> 00:14:58,900 Where does that come from? 258 00:14:58,900 --> 00:15:03,640 So let me just put down there's a paradoxal phosphate 259 00:15:03,640 --> 00:15:08,380 enzyme that can deliver sulfide from systane, for example. 260 00:15:08,380 --> 00:15:11,560 So where does it come from? 261 00:15:11,560 --> 00:15:13,150 What about these proteins? 262 00:15:13,150 --> 00:15:14,860 Can you think of another kind of protein 263 00:15:14,860 --> 00:15:18,910 that you've seen before, that if you have an apoprotein-- 264 00:15:18,910 --> 00:15:20,680 so the metal's not in there, and the metal 265 00:15:20,680 --> 00:15:22,305 doesn't go in during folding. 266 00:15:22,305 --> 00:15:23,680 And there is some where the metal 267 00:15:23,680 --> 00:15:25,850 goes in during folding, some where it doesn't go in 268 00:15:25,850 --> 00:15:27,310 during folding. 269 00:15:27,310 --> 00:15:31,240 What else might you have to do to prepare the active site 270 00:15:31,240 --> 00:15:33,970 to be able to bind the metal? 271 00:15:33,970 --> 00:15:36,814 What kind of a protein might you have to use? 272 00:15:36,814 --> 00:15:38,912 AUDIENCE: Some sort of chaperone [INAUDIBLE].. 273 00:15:38,912 --> 00:15:40,870 JOANNE STUBBE: Yeah, so some sort of chaperone. 274 00:15:40,870 --> 00:15:43,960 And you've all looked at the heat shock proteins. 275 00:15:43,960 --> 00:15:46,210 HSP 70, HSP 40. 276 00:15:46,210 --> 00:15:49,120 Almost all of these things have chaperone proteins 277 00:15:49,120 --> 00:15:53,590 with HSP 40, HSP 70-like activities. 278 00:15:53,590 --> 00:15:56,780 So you require some kind of chaperone. 279 00:15:56,780 --> 00:16:04,030 And this could be HSP 70, HSP 40. 280 00:16:04,030 --> 00:16:07,240 So I'm showing you this for an iron sulfur cluster 281 00:16:07,240 --> 00:16:09,910 because that's who we're going to focus on in the case of iron 282 00:16:09,910 --> 00:16:10,960 homeostasis. 283 00:16:10,960 --> 00:16:16,960 But this is true for many, many metal 284 00:16:16,960 --> 00:16:18,460 clusters that are generated. 285 00:16:18,460 --> 00:16:22,720 And this just shows you the complexity of it. 286 00:16:22,720 --> 00:16:30,430 So here are the pathways in bacteria for generic iron 287 00:16:30,430 --> 00:16:31,600 sulfur clusters. 288 00:16:31,600 --> 00:16:34,810 There are two pathways, one housekeeping, 289 00:16:34,810 --> 00:16:37,750 one under stress conditions. 290 00:16:37,750 --> 00:16:40,870 And you can see how many gene products you need. 291 00:16:40,870 --> 00:16:44,170 And they're involved in different kinds of proteins 292 00:16:44,170 --> 00:16:46,060 that do all of this stuff. 293 00:16:46,060 --> 00:16:48,220 We have things like scaffold proteins, 294 00:16:48,220 --> 00:16:51,010 so if you have to make something really complicated, 295 00:16:51,010 --> 00:16:53,050 you make it on a scaffold first and then 296 00:16:53,050 --> 00:16:54,730 you transfer and you transfer it. 297 00:16:54,730 --> 00:16:58,060 So ligand exchange becomes extremely important. 298 00:16:58,060 --> 00:16:59,080 What about this guy? 299 00:16:59,080 --> 00:17:05,319 This is the cluster for that huge formation 300 00:17:05,319 --> 00:17:09,250 of that beautiful cofactor you saw in the case of nitrogenase 301 00:17:09,250 --> 00:17:12,030 and how to get a carbide in there. 302 00:17:12,030 --> 00:17:16,089 So anyhow, I don't want to see say anything more about that. 303 00:17:16,089 --> 00:17:18,640 But this is all controlled, and I 304 00:17:18,640 --> 00:17:20,980 think this is something that when people 305 00:17:20,980 --> 00:17:24,520 want to study metallocofactors in the chemistry, 306 00:17:24,520 --> 00:17:28,450 they always encounter problems of how to assemble the cluster. 307 00:17:28,450 --> 00:17:33,790 Because if you heterologously express a protein, 308 00:17:33,790 --> 00:17:36,400 it's not a given that the cofactor is 309 00:17:36,400 --> 00:17:38,800 assembled correctly. 310 00:17:38,800 --> 00:17:43,930 So that's what I wanted to say about the generic properties 311 00:17:43,930 --> 00:17:44,650 of metals. 312 00:17:44,650 --> 00:17:47,200 And what I want to say now is just 313 00:17:47,200 --> 00:17:52,660 give you a very brief overview of metal homeostasis. 314 00:17:59,490 --> 00:18:01,080 So this is in general, and then we'll 315 00:18:01,080 --> 00:18:04,670 come back and talk about it specifically with iron. 316 00:18:04,670 --> 00:18:06,120 And so I'm going to say-- 317 00:18:06,120 --> 00:18:07,510 I'm not going to draw this out. 318 00:18:07,510 --> 00:18:11,490 I'm just going to say, see the PowerPoint. 319 00:18:11,490 --> 00:18:15,780 But I want to make a couple of points. 320 00:18:15,780 --> 00:18:18,390 And one of the first things that we 321 00:18:18,390 --> 00:18:23,070 need to think about that's not shown in this picture 322 00:18:23,070 --> 00:18:25,390 is any kind of regulation. 323 00:18:25,390 --> 00:18:29,010 How do we control whether you want metal 324 00:18:29,010 --> 00:18:30,108 or you don't want a metal? 325 00:18:30,108 --> 00:18:31,650 It's the same thing with cholesterol. 326 00:18:31,650 --> 00:18:34,800 How do you control whether we want it or we don't want it? 327 00:18:34,800 --> 00:18:50,160 So control of metal levels can happen transcriptionally, just 328 00:18:50,160 --> 00:18:51,650 like we saw with the SREBP. 329 00:18:55,530 --> 00:18:59,760 So in that picture that I have over there, 330 00:18:59,760 --> 00:19:01,320 I should have redrawn it. 331 00:19:01,320 --> 00:19:05,760 So this is all in the nucleus, and there 332 00:19:05,760 --> 00:19:07,680 is no nucleus in that cartoon, even 333 00:19:07,680 --> 00:19:09,240 though it's a eukaryotic cell. 334 00:19:12,630 --> 00:19:18,840 Transcription factor is they bind metals in some oxidation 335 00:19:18,840 --> 00:19:20,400 state. 336 00:19:20,400 --> 00:19:22,530 And they can be either activators 337 00:19:22,530 --> 00:19:24,300 or they can be repressors. 338 00:19:24,300 --> 00:19:27,300 So there are a lot of people still studying this. 339 00:19:27,300 --> 00:19:33,840 So these can be activation or repression. 340 00:19:33,840 --> 00:19:39,690 And I think almost all organisms use this in a productive way 341 00:19:39,690 --> 00:19:41,250 to control the metals. 342 00:19:41,250 --> 00:19:43,980 We're not going to talk about transcriptional regulation 343 00:19:43,980 --> 00:19:45,600 at all, but it's out there. 344 00:19:45,600 --> 00:19:49,020 It's a real challenge if you have weakly-bound metals, 345 00:19:49,020 --> 00:19:53,400 like you are learning about in recitation this week. 346 00:19:53,400 --> 00:19:57,390 The second thing we have in the cytosol which is also involved 347 00:19:57,390 --> 00:19:59,950 in regulation-- which is again not shown, 348 00:19:59,950 --> 00:20:01,290 so this happens in the cytosol-- 349 00:20:01,290 --> 00:20:06,630 is you have a piece of messenger RNA. 350 00:20:06,630 --> 00:20:08,280 And it turns out-- 351 00:20:08,280 --> 00:20:11,400 many of you probably know, but messenger RNA 352 00:20:11,400 --> 00:20:13,830 has a lot of secondary structures. 353 00:20:17,370 --> 00:20:21,210 So this is a secondary structure, 354 00:20:21,210 --> 00:20:22,840 which is a stem loop. 355 00:20:22,840 --> 00:20:24,120 So this is an RNA. 356 00:20:24,120 --> 00:20:26,130 And this is the five-prime end, and this 357 00:20:26,130 --> 00:20:29,250 is the three-prime end. 358 00:20:29,250 --> 00:20:34,530 And it turns out that if you're going to convert your messenger 359 00:20:34,530 --> 00:20:38,730 RNA into a protein, you want to use the ribosome 360 00:20:38,730 --> 00:20:40,950 and you want to have translation. 361 00:20:40,950 --> 00:20:44,580 And we're going to see that there are structures-- 362 00:20:44,580 --> 00:20:48,270 stem loop structures, in the case of iron-- 363 00:20:48,270 --> 00:20:49,930 that can bind proteins. 364 00:20:49,930 --> 00:20:56,070 And when they bind proteins, what happens is you can alter. 365 00:20:56,070 --> 00:20:57,195 So this could be a protein. 366 00:21:01,290 --> 00:21:07,442 Or you can also, at the three-prime end, bind proteins. 367 00:21:07,442 --> 00:21:08,900 And we're going to talk about this. 368 00:21:08,900 --> 00:21:11,590 So I'm not going to write all of this down. 369 00:21:11,590 --> 00:21:13,680 You're going to see this again. 370 00:21:13,680 --> 00:21:14,880 But you can control-- 371 00:21:14,880 --> 00:21:19,080 you can stop, for example, the translational process 372 00:21:19,080 --> 00:21:20,420 by putting a block over here. 373 00:21:20,420 --> 00:21:21,690 And we'll come back to this. 374 00:21:21,690 --> 00:21:27,300 Or you can stop messenger RNA degradation 375 00:21:27,300 --> 00:21:28,560 by putting a block there. 376 00:21:28,560 --> 00:21:32,160 So again, this is just another level of control 377 00:21:32,160 --> 00:21:34,170 that you guys haven't thought about. 378 00:21:34,170 --> 00:21:39,270 Has anybody seen control of RNA by little structures 379 00:21:39,270 --> 00:21:40,528 and small molecules binding? 380 00:21:40,528 --> 00:21:42,195 Have you seen that before in some class? 381 00:21:42,195 --> 00:21:43,530 AUDIENCE: Ribozymes? 382 00:21:43,530 --> 00:21:44,850 JOANNE STUBBE: Yes. 383 00:21:44,850 --> 00:21:47,880 Riboswitches. 384 00:21:47,880 --> 00:21:50,160 So ribozymes is the catalyst. 385 00:21:50,160 --> 00:21:52,710 All we're talking about here now is preventing 386 00:21:52,710 --> 00:21:54,660 the translational process. 387 00:21:54,660 --> 00:22:02,430 And so what you see, which was discovered by Breaker's lab, 388 00:22:02,430 --> 00:22:03,943 is that you have riboswitches. 389 00:22:03,943 --> 00:22:05,610 They're much more complicated than this. 390 00:22:05,610 --> 00:22:07,230 They have a much bigger structure. 391 00:22:07,230 --> 00:22:11,130 But they can bind things like adenosylcobalamin. 392 00:22:11,130 --> 00:22:14,927 They can bind flavins, all of which 393 00:22:14,927 --> 00:22:17,010 you might want to control just like you might want 394 00:22:17,010 --> 00:22:20,550 to control metal homeostasis. 395 00:22:20,550 --> 00:22:28,210 So metal homeostasis-- this is the regulation part. 396 00:22:28,210 --> 00:22:31,740 So this is regulation. 397 00:22:31,740 --> 00:22:35,610 And then if you look at the cartoon over there-- 398 00:22:35,610 --> 00:22:37,920 again, I'm not going to write down all the details, 399 00:22:37,920 --> 00:22:39,360 but we'll just walk through it. 400 00:22:43,030 --> 00:22:44,530 What do we have to be able to do? 401 00:22:44,530 --> 00:22:49,750 So we have to be able to take metals up into the cell. 402 00:22:49,750 --> 00:22:52,120 Do you think there's one uptake system? 403 00:22:52,120 --> 00:22:53,120 What do you think? 404 00:22:53,120 --> 00:22:53,620 Yeah. 405 00:22:53,620 --> 00:22:55,480 So what you would be surprised is 406 00:22:55,480 --> 00:22:58,720 if you want to take iron into an E. coli, 407 00:22:58,720 --> 00:23:02,890 they're at least iron 5 transporters. 408 00:23:02,890 --> 00:23:08,530 And the issue is, again, not many people have measured 409 00:23:08,530 --> 00:23:11,410 the specificity of all these things and the binding, 410 00:23:11,410 --> 00:23:13,850 and it all depends on the environment. 411 00:23:13,850 --> 00:23:16,240 So this is, I think, an incredibly important area 412 00:23:16,240 --> 00:23:19,360 that needs to have a lot of attention. 413 00:23:19,360 --> 00:23:20,590 We'll see in humans. 414 00:23:20,590 --> 00:23:22,240 We'll also see in bacteria. 415 00:23:22,240 --> 00:23:24,970 Bacteria are desperate for iron. 416 00:23:24,970 --> 00:23:27,070 They have an amazing number of ways 417 00:23:27,070 --> 00:23:30,160 to take iron into the cell. 418 00:23:30,160 --> 00:23:32,590 So once it gets inside, what happens to it? 419 00:23:32,590 --> 00:23:36,050 So the metal can come in. 420 00:23:36,050 --> 00:23:39,190 Here's a metal that's sort of free. 421 00:23:39,190 --> 00:23:42,820 It can form what people call a labile metal pool. 422 00:23:42,820 --> 00:23:46,450 It comes in maybe as aqueous or one of the ligands. 423 00:23:46,450 --> 00:23:48,970 They always have ligands. 424 00:23:48,970 --> 00:23:54,310 it can then form an interaction with all of your metabolites. 425 00:23:54,310 --> 00:23:58,350 So and again, you're thinking about KDs 426 00:23:58,350 --> 00:23:59,350 for all of these things. 427 00:23:59,350 --> 00:24:01,100 Where does it stay? 428 00:24:01,100 --> 00:24:02,620 it depends on the concentrations, 429 00:24:02,620 --> 00:24:05,500 and it depends on the proteins you have, 430 00:24:05,500 --> 00:24:08,020 and what the binding constants are. 431 00:24:08,020 --> 00:24:11,140 Once it gets in, there-- 432 00:24:11,140 --> 00:24:13,560 little things called metallochaperones. 433 00:24:13,560 --> 00:24:15,040 So it picks it up. 434 00:24:15,040 --> 00:24:18,550 A protein can pick up the metal, and then deliver it 435 00:24:18,550 --> 00:24:20,650 in some way to an apoprotein. 436 00:24:20,650 --> 00:24:24,070 So you have a protein with no metal on it at all. 437 00:24:24,070 --> 00:24:26,680 Can there be another protein that delivers the metal? 438 00:24:26,680 --> 00:24:27,910 And the answer is yes. 439 00:24:27,910 --> 00:24:31,420 And where this has been studied in detail in the transition 440 00:24:31,420 --> 00:24:33,340 metals is with copper. 441 00:24:33,340 --> 00:24:35,230 So they have very well-defined copper. 442 00:24:35,230 --> 00:24:39,580 And that's, again, a study in ligand exchange reactions 443 00:24:39,580 --> 00:24:42,010 because it binds here, but you don't 444 00:24:42,010 --> 00:24:43,210 want it to stay over here. 445 00:24:43,210 --> 00:24:46,600 It needs to move over here, and how do you 446 00:24:46,600 --> 00:24:50,530 control the transfer so things end up in the right place? 447 00:24:50,530 --> 00:24:52,630 So say you have an excess of metal. 448 00:24:52,630 --> 00:24:54,640 What happens? 449 00:24:54,640 --> 00:24:57,930 There are different ways of storing the metal. 450 00:24:57,930 --> 00:24:59,770 So storing the metal-- we have ways 451 00:24:59,770 --> 00:25:03,970 of storing zinc, copper, cadmium, 452 00:25:03,970 --> 00:25:06,910 and you'll see we have ways of storing iron. 453 00:25:06,910 --> 00:25:09,250 And so we want to be able to control that. 454 00:25:09,250 --> 00:25:13,510 And we'd like to be able to get it out of storage 455 00:25:13,510 --> 00:25:15,400 when we need it. 456 00:25:15,400 --> 00:25:18,550 And in many cases, depending on the metal, 457 00:25:18,550 --> 00:25:20,020 it's really important we store it 458 00:25:20,020 --> 00:25:23,770 because the metals can be toxic in the reduced state. 459 00:25:23,770 --> 00:25:27,190 And so you want to prevent toxicity to the cell. 460 00:25:27,190 --> 00:25:32,530 So the storage also plays a key role in eukaryotic systems. 461 00:25:32,530 --> 00:25:37,360 We'll see you also have iron transporters into organelles. 462 00:25:37,360 --> 00:25:39,040 It could be into the vacuole. 463 00:25:39,040 --> 00:25:41,110 It could be into the mitochondria. 464 00:25:41,110 --> 00:25:43,630 It could be into the lysosome. 465 00:25:43,630 --> 00:25:46,390 And so that's all controlled. 466 00:25:46,390 --> 00:25:47,980 Just like you have the importers, 467 00:25:47,980 --> 00:25:49,690 we're going to see you have exporters 468 00:25:49,690 --> 00:25:51,880 out of the organelles. 469 00:25:51,880 --> 00:25:56,020 And not shown here-- again, this is not a very good cartoon-- 470 00:25:56,020 --> 00:25:57,730 you could have exporters. 471 00:25:57,730 --> 00:26:01,150 You could control elevated levels-- in some cases, 472 00:26:01,150 --> 00:26:02,950 not in humans-- 473 00:26:02,950 --> 00:26:06,970 but by exporting the metals out of the cell. 474 00:26:06,970 --> 00:26:10,030 So there are many levels. 475 00:26:10,030 --> 00:26:11,830 Doesn't matter what the metal is. 476 00:26:11,830 --> 00:26:15,760 You see these kinds of mechanisms in all cases. 477 00:26:15,760 --> 00:26:18,490 And we'll focus on the case of iron 478 00:26:18,490 --> 00:26:22,090 in both humans and bacteria. 479 00:26:22,090 --> 00:26:25,870 So that's the end of the introductory lecture 480 00:26:25,870 --> 00:26:30,820 on metal homeostasis. 481 00:26:30,820 --> 00:26:38,200 And now what I want to do, we're going to focus on iron. 482 00:26:38,200 --> 00:26:41,560 And as I told you at the very beginning, 483 00:26:41,560 --> 00:26:46,480 we're initially going to look at a few pieces of information 484 00:26:46,480 --> 00:26:50,020 about iron specifically, rather than metals in general. 485 00:26:50,020 --> 00:26:52,180 But all the principles we talked about in general 486 00:26:52,180 --> 00:26:54,400 are applicable to iron. 487 00:26:54,400 --> 00:26:59,020 And then we're going to look at what happens in humans. 488 00:26:59,020 --> 00:27:02,170 And specifically, after you get the big picture-- 489 00:27:02,170 --> 00:27:03,298 how much iron do we have? 490 00:27:03,298 --> 00:27:04,090 Where do we get it? 491 00:27:04,090 --> 00:27:05,890 How much comes from the iron? 492 00:27:05,890 --> 00:27:07,180 Is it recycled? 493 00:27:07,180 --> 00:27:07,720 Et cetera. 494 00:27:07,720 --> 00:27:10,480 Just like we did with cholesterol. 495 00:27:10,480 --> 00:27:14,050 And we're going to be focusing on uptake into the cell, 496 00:27:14,050 --> 00:27:17,200 and we will see there are two ways of taking up iron 497 00:27:17,200 --> 00:27:20,130 into the cell in the plus 2 state. 498 00:27:20,130 --> 00:27:23,770 And there are iron 2 transporters. 499 00:27:23,770 --> 00:27:29,170 And we'll also see that there's a protein called transferrin 500 00:27:29,170 --> 00:27:32,350 that binds iron in the plus 3 state. 501 00:27:32,350 --> 00:27:35,200 So the oxidation state is distinct. 502 00:27:35,200 --> 00:27:38,080 You then have an iron 3 protein complex, 503 00:27:38,080 --> 00:27:40,510 and that gets taken up into the cell 504 00:27:40,510 --> 00:27:44,660 by receptor-mediated endocytosis by mechanisms quite 505 00:27:44,660 --> 00:27:50,030 similar to what you've seen with the LDL receptor we have, 506 00:27:50,030 --> 00:27:53,950 a receptor that recognizes this a little protein called 507 00:27:53,950 --> 00:27:54,450 transferrin. 508 00:27:54,450 --> 00:27:55,868 And we'll look at that. 509 00:27:55,868 --> 00:27:57,410 And then we're going to do in the end 510 00:27:57,410 --> 00:27:59,990 is talk about, how is iron regulated? 511 00:27:59,990 --> 00:28:03,890 We'll see there are a number of mechanisms 512 00:28:03,890 --> 00:28:07,340 that regulate everything iron homeostasis, 513 00:28:07,340 --> 00:28:09,890 and we're going to focus on one regulation 514 00:28:09,890 --> 00:28:13,690 at the translational level, like we were just talking about 515 00:28:13,690 --> 00:28:14,660 up here. 516 00:28:14,660 --> 00:28:19,340 So that's where we're going in the next couple of lectures. 517 00:28:19,340 --> 00:28:23,055 And so I just want to make a few points about iron. 518 00:28:23,055 --> 00:28:24,680 And so the first thing we're looking at 519 00:28:24,680 --> 00:28:32,500 is some general issues about iron, the properties of iron 520 00:28:32,500 --> 00:28:34,070 that we need to think about. 521 00:28:34,070 --> 00:28:35,840 So we're going to look at the properties. 522 00:28:45,580 --> 00:28:49,700 And what did we learn in the last lecture? 523 00:28:49,700 --> 00:28:54,610 We learned that iron is abundant. 524 00:28:54,610 --> 00:29:03,460 We know that 80% of the core of the Earth is iron. 525 00:29:03,460 --> 00:29:10,000 But we also learned that the crust of the earth-- 526 00:29:10,000 --> 00:29:12,830 the fourth predominant metal is iron. 527 00:29:12,830 --> 00:29:14,150 And so it's all over the place. 528 00:29:14,150 --> 00:29:16,780 We also learned it's unavailable because we 529 00:29:16,780 --> 00:29:19,660 move from an anaerobic into an oxygen world, 530 00:29:19,660 --> 00:29:24,320 and it becomes oxidized, and the solubility goes way down. 531 00:29:24,320 --> 00:29:26,050 So iron is abundant. 532 00:29:29,410 --> 00:29:34,450 And we know that we have many, many cofactors, 533 00:29:34,450 --> 00:29:35,860 but it's unavailable. 534 00:29:41,230 --> 00:29:43,810 And if you look, an example of this-- 535 00:29:43,810 --> 00:29:52,660 if you take iron 3 aquated at pH 7, what you see 536 00:29:52,660 --> 00:30:00,400 is the solubility is 10 to the minus 18th molar. 537 00:30:00,400 --> 00:30:03,160 So it's not very soluble. 538 00:30:03,160 --> 00:30:06,490 And again, this poses the problem, 539 00:30:06,490 --> 00:30:10,360 not for us, but for bacteria who are desperately 540 00:30:10,360 --> 00:30:15,040 trying to get iron, how do you get iron from the environment 541 00:30:15,040 --> 00:30:17,110 where it's insoluble? 542 00:30:17,110 --> 00:30:20,740 So what is one of nature's solutions that you've already 543 00:30:20,740 --> 00:30:24,490 discussed to obtaining iron? 544 00:30:24,490 --> 00:30:27,440 You talked about in the first half of the course. 545 00:30:27,440 --> 00:30:28,473 AUDIENCE: Siderophores? 546 00:30:28,473 --> 00:30:29,890 JOANNE STUBBE: Siderophores, yeah. 547 00:30:29,890 --> 00:30:31,090 So what do we know? 548 00:30:31,090 --> 00:30:43,030 So a solution for the bacteria and fungi is siderophores. 549 00:30:43,030 --> 00:30:45,310 And which siderophore-- do you remember which one 550 00:30:45,310 --> 00:30:46,720 you talked about in detail? 551 00:30:46,720 --> 00:30:48,365 AUDIENCE: Enterobactin. 552 00:30:48,365 --> 00:30:50,440 JOANNE STUBBE: Enterobactin, yeah. 553 00:30:50,440 --> 00:30:52,870 So they estimate that there are greater-- they 554 00:30:52,870 --> 00:30:54,220 have all kinds of structures. 555 00:30:54,220 --> 00:30:58,690 You saw a structure where you had 556 00:30:58,690 --> 00:31:02,830 a cyclical structure with some serines making ester linkages. 557 00:31:02,830 --> 00:31:06,340 Does anybody remember what the KD was for iron? 558 00:31:06,340 --> 00:31:09,220 This goes into today's recitation section-- 559 00:31:09,220 --> 00:31:12,550 today and yesterday's recitation section. 560 00:31:12,550 --> 00:31:14,340 How does it bind? 561 00:31:14,340 --> 00:31:16,260 What oxidation state does it bind in? 562 00:31:22,960 --> 00:31:26,590 So I'm not going to talk very much about siderophores, 563 00:31:26,590 --> 00:31:31,180 but we will see that in the next lecture after this one. 564 00:31:31,180 --> 00:31:37,710 So the iron, in general, binds in the plus 3 oxidation state. 565 00:31:37,710 --> 00:31:38,920 And the KD-- 566 00:31:38,920 --> 00:31:42,430 I don't remember what it is for enterobactin specifically. 567 00:31:42,430 --> 00:31:45,520 For some reason, the number of 10 to the minus 52 568 00:31:45,520 --> 00:31:46,413 sticks in my mind. 569 00:31:46,413 --> 00:31:47,080 Is that correct? 570 00:31:47,080 --> 00:31:48,825 Or is it 10 to the minus 38? 571 00:31:48,825 --> 00:31:50,940 AUDIENCE: Well, it depends on pH [INAUDIBLE].. 572 00:31:50,940 --> 00:31:53,290 It's minus 52 or minus 49 recorded, 573 00:31:53,290 --> 00:31:58,322 but then it's in the minus 20s at pH 7. 574 00:31:58,322 --> 00:32:00,780 JOANNE STUBBE: So what's the one that's 10 to the minus 52? 575 00:32:03,740 --> 00:32:04,880 All right. 576 00:32:04,880 --> 00:32:05,630 How about this? 577 00:32:09,290 --> 00:32:11,047 So this is an interesting problem. 578 00:32:11,047 --> 00:32:13,130 You're going to be looking at this in class today. 579 00:32:13,130 --> 00:32:16,010 How do you measure that? 580 00:32:16,010 --> 00:32:17,365 Do you think that's easy? 581 00:32:17,365 --> 00:32:18,740 Do you think you're going to have 582 00:32:18,740 --> 00:32:20,173 any way of detecting things? 583 00:32:20,173 --> 00:32:22,340 So this is where you've got to be creative and think 584 00:32:22,340 --> 00:32:25,040 about what you're learning about in recitation. 585 00:32:25,040 --> 00:32:26,780 So these things-- the bottom line 586 00:32:26,780 --> 00:32:29,930 is, everything is dependent on the ligands 587 00:32:29,930 --> 00:32:32,360 and obviously on the pH. 588 00:32:32,360 --> 00:32:34,490 But they bind like a son of a gun. 589 00:32:34,490 --> 00:32:38,720 And that's because these bacteria 590 00:32:38,720 --> 00:32:41,150 need to get iron to survive. 591 00:32:41,150 --> 00:32:45,420 So I think that's pretty important. 592 00:32:45,420 --> 00:32:48,560 The second thing, again, I wanted to point out 593 00:32:48,560 --> 00:32:57,420 is there exists a diversity of iron cofactors. 594 00:33:00,750 --> 00:33:06,300 And you've seen these in the first few lectures. 595 00:33:06,300 --> 00:33:08,730 I've blown through a number of structures. 596 00:33:08,730 --> 00:33:11,470 But they're found in general ways. 597 00:33:11,470 --> 00:33:13,530 What is the one that you're all familiar with? 598 00:33:13,530 --> 00:33:18,036 Where do you see iron that you all think about? 599 00:33:18,036 --> 00:33:18,710 AUDIENCE: Heme. 600 00:33:18,710 --> 00:33:19,835 JOANNE STUBBE: Heme, right. 601 00:33:19,835 --> 00:33:22,050 Why do you think about it? 602 00:33:22,050 --> 00:33:25,140 Why do you know heme and not some of the other? 603 00:33:25,140 --> 00:33:27,390 So this is heme. 604 00:33:27,390 --> 00:33:28,760 This is my protoporphyrin IX. 605 00:33:31,690 --> 00:33:33,690 Actually I can draw the structure of [INAUDIBLE] 606 00:33:33,690 --> 00:33:36,060 but I'm not going to draw it. 607 00:33:36,060 --> 00:33:38,400 I'm good at drawing structures of organic molecules, 608 00:33:38,400 --> 00:33:39,608 but I'm not going to draw it. 609 00:33:39,608 --> 00:33:40,920 It's not relevant. 610 00:33:40,920 --> 00:33:43,250 But why do you know heme? 611 00:33:43,250 --> 00:33:45,370 AUDIENCE: It's [INAUDIBLE] It's easy to see. 612 00:33:45,370 --> 00:33:46,703 JOANNE STUBBE: It's easy to see. 613 00:33:46,703 --> 00:33:47,220 That's it. 614 00:33:47,220 --> 00:33:49,380 Why do we know so much about heme? 615 00:33:49,380 --> 00:33:50,460 Because it's easy to see. 616 00:33:50,460 --> 00:33:53,780 Its extinction coefficient is like over 100,000. 617 00:33:53,780 --> 00:33:56,520 So those are the ones that people saw immediately. 618 00:33:56,520 --> 00:33:57,420 You prick yourself. 619 00:33:57,420 --> 00:33:58,540 It's blue or it's red. 620 00:33:58,540 --> 00:34:00,180 Your blood is blue or it's red. 621 00:34:00,180 --> 00:34:07,800 So this has a high extinction coefficient. 622 00:34:07,800 --> 00:34:13,770 So everybody knows we reversibly bind oxygen, 623 00:34:13,770 --> 00:34:17,150 but hemes have an amazing diversity. 624 00:34:17,150 --> 00:34:19,710 Where have we seen heme before? 625 00:34:19,710 --> 00:34:23,580 We've seen it, if you remember, in cholesterol biosynthesis 626 00:34:23,580 --> 00:34:26,139 in the last 19 steps. 627 00:34:26,139 --> 00:34:28,560 We got to get rid of three methyl groups. 628 00:34:28,560 --> 00:34:31,080 All of those are heme enzymes which 629 00:34:31,080 --> 00:34:35,280 catalyze hydroxylation of unactivated carbon hydrogen 630 00:34:35,280 --> 00:34:35,920 bonds. 631 00:34:35,920 --> 00:34:39,780 So hemes can reversibly bind oxygen, 632 00:34:39,780 --> 00:34:42,420 but they can also do this really tough chemistry. 633 00:34:42,420 --> 00:34:44,760 And how did they do that? 634 00:34:44,760 --> 00:34:49,050 They're controlled by the environment around the heme. 635 00:34:49,050 --> 00:34:53,940 So why haven't we seen the other places where-- 636 00:34:53,940 --> 00:34:58,620 why don't we think about the other cofactors that involve? 637 00:34:58,620 --> 00:35:09,330 So we have non-heme iron, and this can be mono or dinuclear. 638 00:35:12,390 --> 00:35:14,140 And why don't we think about those? 639 00:35:14,140 --> 00:35:15,850 So no heme. 640 00:35:15,850 --> 00:35:21,540 So you have oxygen, nitrogen, histidine ligands, 641 00:35:21,540 --> 00:35:25,710 hydrazine ligands, perhaps, sulfur ligands. 642 00:35:25,710 --> 00:35:28,930 And you don't see this because they're not colored. 643 00:35:28,930 --> 00:35:31,500 In the plus 2 oxidation state, they're really hard to see. 644 00:35:31,500 --> 00:35:34,890 But for every heme-dependent system, 645 00:35:34,890 --> 00:35:38,310 there are mono and dinuclear non-heme iron systems 646 00:35:38,310 --> 00:35:41,610 that are probably more prevalent that can do the same chemistry. 647 00:35:41,610 --> 00:35:45,690 So we don't see them, that doesn't mean they're not there, 648 00:35:45,690 --> 00:35:48,330 and it doesn't mean they're not important. 649 00:35:48,330 --> 00:35:51,220 It's just they're much harder to study. 650 00:35:51,220 --> 00:35:54,480 So these things are very prevalent, 651 00:35:54,480 --> 00:36:02,010 and they do the same chemistry as hemes. 652 00:36:02,010 --> 00:36:05,850 So I showed you one where you could reversibly bind 653 00:36:05,850 --> 00:36:07,860 oxygen. Remember those little worms we 654 00:36:07,860 --> 00:36:10,290 saw in the slide that can reversibly bind oxygens, 655 00:36:10,290 --> 00:36:12,810 just like hemoglobin? 656 00:36:12,810 --> 00:36:18,510 You can hydroxylate unactivated carbon-hydrogen bonds. 657 00:36:18,510 --> 00:36:20,610 And where do you see that? 658 00:36:20,610 --> 00:36:23,450 Nowadays, one sees at all over the place 659 00:36:23,450 --> 00:36:27,480 because DNA and RNA modification is all 660 00:36:27,480 --> 00:36:31,740 mediated by, in many cases, alpha-Ketoglutarate, non-heme 661 00:36:31,740 --> 00:36:33,170 iron, dioxygenase. 662 00:36:33,170 --> 00:36:35,040 So I don't want to say any more about that, 663 00:36:35,040 --> 00:36:37,410 except they're extremely important, 664 00:36:37,410 --> 00:36:38,700 and they're hard to study. 665 00:36:38,700 --> 00:36:42,610 But we have really good tools to study all of these things. 666 00:36:42,610 --> 00:36:45,940 And then the other one, which we've just been talking about, 667 00:36:45,940 --> 00:36:52,320 which is the focus of the section on iron homeostasis, 668 00:36:52,320 --> 00:36:54,290 is iron sulfur. 669 00:36:54,290 --> 00:36:56,610 And so iron sulfur, for decades, was 670 00:36:56,610 --> 00:36:59,490 thought to be oxidation reduction electron transfer, 671 00:36:59,490 --> 00:37:01,090 which we talked about. 672 00:37:01,090 --> 00:37:04,610 But we now know, again, through these radical SAM proteins, 673 00:37:04,610 --> 00:37:06,420 there are just basically hundreds 674 00:37:06,420 --> 00:37:11,070 of complex radical reactions that we'd just be scratching 675 00:37:11,070 --> 00:37:13,480 the surface in learning. 676 00:37:13,480 --> 00:37:15,690 So this is also on there. 677 00:37:15,690 --> 00:37:23,370 Again, greater than 100,000 reactions, and these reactions 678 00:37:23,370 --> 00:37:24,700 are chemically interesting. 679 00:37:24,700 --> 00:37:27,610 So from a chemical point of view, 680 00:37:27,610 --> 00:37:31,920 the frontier, in my opinion, is not in the organic side at all. 681 00:37:31,920 --> 00:37:34,057 It's in the metal side. 682 00:37:34,057 --> 00:37:35,390 I think we don't have that much. 683 00:37:35,390 --> 00:37:38,310 You know, we have a little bit of intuition about what 684 00:37:38,310 --> 00:37:40,860 happens, but what we're seeing is things 685 00:37:40,860 --> 00:37:44,490 that we didn't expect to happen at all. 686 00:37:44,490 --> 00:37:46,830 We're seeing it in proteins, and then people 687 00:37:46,830 --> 00:37:49,500 are trying to figure out whether they 688 00:37:49,500 --> 00:37:51,510 can make the same things happen in solution 689 00:37:51,510 --> 00:37:54,900 and take advantage of all of this. 690 00:37:54,900 --> 00:37:59,978 So we have a diversity of metallocofactors. 691 00:37:59,978 --> 00:38:00,770 What about ligands? 692 00:38:04,050 --> 00:38:07,640 And almost anything can be a ligand. 693 00:38:07,640 --> 00:38:12,140 So it can be a protein, or it can be a small molecule 694 00:38:12,140 --> 00:38:13,380 metabolite. 695 00:38:13,380 --> 00:38:15,410 So you can have proteins. 696 00:38:15,410 --> 00:38:18,570 What are the ligands you might think you would find on iron? 697 00:38:23,300 --> 00:38:26,978 Tell me what the amino-- give me the one letter codes. 698 00:38:26,978 --> 00:38:28,400 AUDIENCE: D, E. 699 00:38:28,400 --> 00:38:31,160 JOANNE STUBBE: D, E. OK. 700 00:38:31,160 --> 00:38:34,310 Give me a D. Give me an E. What else? 701 00:38:34,310 --> 00:38:34,850 What else? 702 00:38:34,850 --> 00:38:35,150 Come on. 703 00:38:35,150 --> 00:38:35,730 Let's go. 704 00:38:39,102 --> 00:38:39,602 AUDIENCE: H. 705 00:38:39,602 --> 00:38:40,570 AUDIENCE: C. 706 00:38:40,570 --> 00:38:43,360 JOANNE STUBBE: H. They don't have 707 00:38:43,360 --> 00:38:45,670 to be in alphabetical order. 708 00:38:45,670 --> 00:38:46,170 AUDIENCE: C. 709 00:38:46,170 --> 00:38:46,430 AUDIENCE: C. 710 00:38:46,430 --> 00:38:46,930 AUDIENCE: C. 711 00:38:46,930 --> 00:38:53,350 JOANNE STUBBE: C. Try one more. 712 00:38:53,350 --> 00:38:55,600 You'll see it in a minute. 713 00:38:55,600 --> 00:38:57,950 AUDIENCE: [INAUDIBLE] for water. 714 00:38:57,950 --> 00:38:59,110 JOANNE STUBBE: Water? 715 00:38:59,110 --> 00:39:00,223 Yeah, water is wonderful. 716 00:39:00,223 --> 00:39:01,640 I'm not going to write down water. 717 00:39:01,640 --> 00:39:02,780 That's not an amino acid. 718 00:39:02,780 --> 00:39:04,340 So how about tyrosine? 719 00:39:04,340 --> 00:39:08,420 So what's amazing now is we even see things like arginine. 720 00:39:08,420 --> 00:39:12,620 That has a PKA of between 10 and 11. 721 00:39:12,620 --> 00:39:16,190 And the Drennan Lab has found several proteins 722 00:39:16,190 --> 00:39:18,140 where arginine appears to be-- 723 00:39:18,140 --> 00:39:20,960 and other people-- a ligand. 724 00:39:20,960 --> 00:39:22,790 So we have a diversity of ligands 725 00:39:22,790 --> 00:39:24,830 from the amino acid side chains. 726 00:39:24,830 --> 00:39:26,480 If you look at metabolites, we've 727 00:39:26,480 --> 00:39:29,690 already talked about citrate. 728 00:39:29,690 --> 00:39:32,030 Is that how you spell citrate? 729 00:39:32,030 --> 00:39:35,240 Citrate is in the TCE cycle. 730 00:39:35,240 --> 00:39:40,470 Alpha-Ketoglutarate-- that's also in the TCA cycle. 731 00:39:40,470 --> 00:39:42,260 I'm not going to draw this, but these 732 00:39:42,260 --> 00:39:46,310 are major players that mediate chemistry 733 00:39:46,310 --> 00:39:47,840 on iron-independent systems. 734 00:39:47,840 --> 00:39:51,770 So we have a diversity of these things. 735 00:39:51,770 --> 00:39:57,400 What about the geometry of all of these things? 736 00:39:57,400 --> 00:40:00,140 The geometry can be octahedral. 737 00:40:00,140 --> 00:40:02,600 It can be tetrahedral. 738 00:40:02,600 --> 00:40:06,350 It can be trigonal, bipyramidal, et cetera. 739 00:40:06,350 --> 00:40:08,870 Almost anything you can imagine, you can find it. 740 00:40:08,870 --> 00:40:11,570 Nature has figured out how to use this. 741 00:40:14,550 --> 00:40:17,420 In that paper by Yi Lu, where I told you 742 00:40:17,420 --> 00:40:21,170 they were changing the redox potential over 2 volts? 743 00:40:21,170 --> 00:40:23,450 One of the things they invoked was figuring out 744 00:40:23,450 --> 00:40:28,190 how to strain the metal to enhance the ability 745 00:40:28,190 --> 00:40:30,350 to reduce it to change its confirmation, which 746 00:40:30,350 --> 00:40:33,110 might be more favorable. 747 00:40:33,110 --> 00:40:36,380 So you have just really a huge number of things 748 00:40:36,380 --> 00:40:45,360 that you can deal with in these metals that I think 749 00:40:45,360 --> 00:40:49,260 allow the huge diversity of reactions 750 00:40:49,260 --> 00:40:52,530 that we're still unraveling, actually. 751 00:40:52,530 --> 00:40:57,990 So the other thing about iron is that, 752 00:40:57,990 --> 00:41:01,980 what are the oxidation states of iron? 753 00:41:01,980 --> 00:41:03,750 So we have the redox states. 754 00:41:03,750 --> 00:41:05,250 I can't remember what number I'm on. 755 00:41:09,550 --> 00:41:12,980 So we've just been going over and over again, 756 00:41:12,980 --> 00:41:15,630 these are the two common states. 757 00:41:15,630 --> 00:41:17,490 Iron 2, iron 3. 758 00:41:17,490 --> 00:41:20,410 And in the last lecture, we talked 759 00:41:20,410 --> 00:41:22,840 about other oxidation states. 760 00:41:22,840 --> 00:41:26,440 And it turns out if you look at the chemistry of what's 761 00:41:26,440 --> 00:41:28,060 going on, and you want to hydroxylate 762 00:41:28,060 --> 00:41:31,270 an unactivated carbon-hydrogen bond, 763 00:41:31,270 --> 00:41:36,940 you frequently see iron 4. 764 00:41:36,940 --> 00:41:43,300 And usually iron 4 is not sitting around 765 00:41:43,300 --> 00:41:45,340 in the test tube. 766 00:41:45,340 --> 00:41:48,100 It's activated, so it wants to get reduced. 767 00:41:48,100 --> 00:41:51,400 And that's what allows it to be able to do the chemistry. 768 00:41:51,400 --> 00:41:54,733 So unlike these guys, these are the workhorses 769 00:41:54,733 --> 00:41:55,900 you see over and over again. 770 00:41:55,900 --> 00:42:01,000 That's what we're going to see in iron homeostasis in general. 771 00:42:01,000 --> 00:42:07,990 But one also sees iron 1 or iron 0. 772 00:42:07,990 --> 00:42:11,140 And where does one see iron 1 or iron 0? 773 00:42:11,140 --> 00:42:15,670 Again, remember those ligands on the hydrogenase I showed you? 774 00:42:15,670 --> 00:42:18,640 Iron hydrogenase is what I showed you. 775 00:42:18,640 --> 00:42:20,290 There's an iron nickel hydrogenase. 776 00:42:20,290 --> 00:42:23,200 There's an iron-only hydrogenase. 777 00:42:23,200 --> 00:42:26,440 People are really interested in this for the energy problem. 778 00:42:26,440 --> 00:42:30,880 Hydrogenases are really, really fast. 779 00:42:30,880 --> 00:42:32,050 And what kind of ligands? 780 00:42:32,050 --> 00:42:34,570 Remember, we discussed this. 781 00:42:34,570 --> 00:42:40,173 And the ligands are going to control the chemistry. 782 00:42:40,173 --> 00:42:41,590 What kinds of ligands did you see? 783 00:42:41,590 --> 00:42:44,710 You saw a CO in cyanide. 784 00:42:44,710 --> 00:42:49,720 So that allows very different properties of the metals, 785 00:42:49,720 --> 00:42:51,880 in terms of the spin states you'll see, 786 00:42:51,880 --> 00:42:54,070 that allows different chemistry to happen. 787 00:42:54,070 --> 00:43:00,850 So let's just recall we have CO in cyanide ligands. 788 00:43:00,850 --> 00:43:05,230 So again, this is not the norm. 789 00:43:05,230 --> 00:43:07,960 But there are many systems where these have now been 790 00:43:07,960 --> 00:43:11,530 formed in unusual bacteria. 791 00:43:11,530 --> 00:43:13,860 We don't see these ligands, at least 792 00:43:13,860 --> 00:43:19,180 I don't think, in any eukaryotic systems. 793 00:43:19,180 --> 00:43:23,040 So the other thing that you need to think about with metals, 794 00:43:23,040 --> 00:43:25,040 if you get into it and start thinking about it-- 795 00:43:25,040 --> 00:43:28,060 and this is key to really, how do you know you have an iron 4? 796 00:43:28,060 --> 00:43:30,250 How do you know you have an iron 0? 797 00:43:30,250 --> 00:43:33,790 How do you study whether it's iron 2, iron 3? 798 00:43:33,790 --> 00:43:37,210 And that's different dependent on the spins states, 799 00:43:37,210 --> 00:43:42,250 because you have dielectrons associated with both the iron 2 800 00:43:42,250 --> 00:43:43,610 state and the iron 3 state. 801 00:43:43,610 --> 00:43:46,210 So if you go back into freshman chemistry, 802 00:43:46,210 --> 00:43:50,875 or if you've had 5.03, you need to think about the spin states. 803 00:43:53,500 --> 00:44:03,070 And what we have is high spin and we have low spin states. 804 00:44:03,070 --> 00:44:07,780 And this is dependent on the ligands. 805 00:44:07,780 --> 00:44:09,680 So this is going to be ligand-dependent. 806 00:44:13,700 --> 00:44:23,050 And if you look at iron 2, you have six electrons 807 00:44:23,050 --> 00:44:24,890 in the d orbitals. 808 00:44:24,890 --> 00:44:32,620 If you look at iron 3, you have five electrons. 809 00:44:32,620 --> 00:44:34,390 And so if you look at the d orbitals 810 00:44:34,390 --> 00:44:42,130 in an octahedral field, depending on the ligands, 811 00:44:42,130 --> 00:44:45,310 the energetics of the d orbitals are quite distinct. 812 00:44:45,310 --> 00:44:49,460 Again, we're not going to talk about this in any detail. 813 00:44:49,460 --> 00:44:55,840 But what you can do, then, is if you want to put in five, 814 00:44:55,840 --> 00:44:59,410 depending on what the energy differences are, 815 00:44:59,410 --> 00:45:04,600 they might be all unpaired, or they could be paired. 816 00:45:04,600 --> 00:45:09,250 So this unpaired is high spin, and the paired is low spin. 817 00:45:09,250 --> 00:45:11,620 Do you think they're different spectroscopically? 818 00:45:11,620 --> 00:45:12,730 The answer is yes. 819 00:45:12,730 --> 00:45:15,160 And we have lots of physical biochemical tools 820 00:45:15,160 --> 00:45:18,670 that allow us to look at the differences between all 821 00:45:18,670 --> 00:45:19,360 of these things. 822 00:45:19,360 --> 00:45:24,400 And so this is, again, an active area of research. 823 00:45:24,400 --> 00:45:26,980 So the last thing I want to talk about in terms 824 00:45:26,980 --> 00:45:31,900 of iron properties are going to be key 825 00:45:31,900 --> 00:45:36,190 for us thinking about module seven. 826 00:45:36,190 --> 00:45:39,130 So there are two kinds of iron properties 827 00:45:39,130 --> 00:45:43,520 that you will be introduced to this semester. 828 00:45:43,520 --> 00:45:45,840 So we're looking at, now, the chemical diversity. 829 00:45:55,910 --> 00:46:00,680 And so one of the things is that, remember, 830 00:46:00,680 --> 00:46:02,390 when we're in an anaerobic world, 831 00:46:02,390 --> 00:46:05,600 we could use iron 2 because we didn't have to worry 832 00:46:05,600 --> 00:46:07,040 about any redox chemistry. 833 00:46:07,040 --> 00:46:11,070 Now in humans, we're in an aeorbic world, 834 00:46:11,070 --> 00:46:15,540 and we're faced with this issue of reduced metals and oxygen. 835 00:46:15,540 --> 00:46:21,170 So what you're going to see is, in the presence of oxygen-- 836 00:46:21,170 --> 00:46:23,870 and we're going to go into this in some detail in module seven. 837 00:46:23,870 --> 00:46:25,745 We're not going to spend a lot of time on it. 838 00:46:25,745 --> 00:46:30,240 But you learn a little bit about what we call reactive oxygen 839 00:46:30,240 --> 00:46:30,740 species. 840 00:46:33,380 --> 00:46:39,110 In the presence of oxygen, you can form iron 3, 841 00:46:39,110 --> 00:46:42,470 and you can form a molecule that looks like that. 842 00:46:42,470 --> 00:46:43,580 That's super oxide. 843 00:46:49,200 --> 00:46:56,460 And many people call this a reactive oxygen species. 844 00:46:56,460 --> 00:46:59,340 It depends on its environment whether they're reactive. 845 00:46:59,340 --> 00:47:01,800 So again, from a chemical perspective, 846 00:47:01,800 --> 00:47:03,600 I think thinking about what's possible 847 00:47:03,600 --> 00:47:06,690 is really the key in the kinetics, and what's around-- 848 00:47:06,690 --> 00:47:09,090 the concentrations, the kinetics, what's around. 849 00:47:09,090 --> 00:47:14,130 That's what has been missing in the reactive oxygen field. 850 00:47:14,130 --> 00:47:18,660 And for example, in the presence of protons-- 851 00:47:18,660 --> 00:47:20,700 we'll talk about this in detail, I'm 852 00:47:20,700 --> 00:47:25,740 not balancing the equations-- we can form another reactive thing 853 00:47:25,740 --> 00:47:28,980 that's considered a reactive oxygen species, which 854 00:47:28,980 --> 00:47:30,940 is hydrogen peroxide. 855 00:47:30,940 --> 00:47:33,270 And I'll show you that that really, 856 00:47:33,270 --> 00:47:36,240 in one or two cases in proteins, that can be very reactive. 857 00:47:36,240 --> 00:47:40,690 But in most cases, it's not all that reactive at all. 858 00:47:40,690 --> 00:47:43,800 And what we will see is iron 2 can 859 00:47:43,800 --> 00:47:46,500 react with hydrogen peroxide. 860 00:47:46,500 --> 00:47:48,570 Again, I'm not balancing my equations. 861 00:47:48,570 --> 00:47:51,300 We'll come back to this later on. 862 00:47:51,300 --> 00:47:55,110 But here's where we do form a reactive oxygen species. 863 00:47:55,110 --> 00:47:57,390 And this is hydroxide radical. 864 00:47:57,390 --> 00:47:59,220 And hydroxide radical, we'll see, 865 00:47:59,220 --> 00:48:01,470 can react with anything it hits. 866 00:48:01,470 --> 00:48:03,090 So this is really reactive. 867 00:48:03,090 --> 00:48:06,210 So all I'm pointing out here is you're forming species. 868 00:48:06,210 --> 00:48:07,260 They're all reactive. 869 00:48:07,260 --> 00:48:10,068 All molecules are reactive to a certain extent, 870 00:48:10,068 --> 00:48:11,985 and you need to put yourself into the context. 871 00:48:11,985 --> 00:48:15,810 So this is really a reactive oxygen species. 872 00:48:15,810 --> 00:48:21,660 And these guys are the focus of module seven 873 00:48:21,660 --> 00:48:26,940 where you'll be introduced to the fact 874 00:48:26,940 --> 00:48:31,320 that hydrogen peroxide can, in some way, 875 00:48:31,320 --> 00:48:32,730 be used to kill bacteria. 876 00:48:32,730 --> 00:48:34,420 We're going to see how that's done. 877 00:48:34,420 --> 00:48:37,260 But hydrogen peroxide is also now thought 878 00:48:37,260 --> 00:48:40,530 to be a second messenger in a signaling agent. 879 00:48:40,530 --> 00:48:43,410 So again, it's all about homeostasis. 880 00:48:43,410 --> 00:48:46,260 So with iron diversity, we've talked 881 00:48:46,260 --> 00:48:48,240 about hydroxylation in the cholesterol 882 00:48:48,240 --> 00:48:50,010 biosynthetic pathway. 883 00:48:50,010 --> 00:48:54,780 We're going to be focused now on this kind of redox chemistry. 884 00:48:54,780 --> 00:48:58,710 And so that's all I want to tell you about in terms 885 00:48:58,710 --> 00:49:00,480 of introduction to iron. 886 00:49:00,480 --> 00:49:04,530 All the properties we talked about-- wrap, exchange, 887 00:49:04,530 --> 00:49:06,260 the exchange reactions, et cetera-- 888 00:49:06,260 --> 00:49:07,718 you need to think about when you're 889 00:49:07,718 --> 00:49:09,780 thinking about iron, as well. 890 00:49:09,780 --> 00:49:14,040 So what I want to do now- so going away 891 00:49:14,040 --> 00:49:18,900 from these general ideas about how iron works, 892 00:49:18,900 --> 00:49:24,030 and we want to go into an overview in humans. 893 00:49:30,140 --> 00:49:33,320 And the first thing, in many of these cases, 894 00:49:33,320 --> 00:49:35,100 the pictures are really complicated. 895 00:49:35,100 --> 00:49:38,120 So I urge you to pull out your PowerPoint slides 896 00:49:38,120 --> 00:49:40,910 and look at them, and then just annotate them a little more. 897 00:49:40,910 --> 00:49:43,080 Because I mean otherwise, I won't get through. 898 00:49:43,080 --> 00:49:47,240 I'll spend all my time drawing the same pictures on the board. 899 00:49:47,240 --> 00:49:51,290 So one of the things we care about in this section 900 00:49:51,290 --> 00:49:52,720 is iron distribution. 901 00:49:55,490 --> 00:50:00,040 We cared about that with cholesterol, as well. 902 00:50:00,040 --> 00:50:03,620 So this was taken out of some textbook, 903 00:50:03,620 --> 00:50:04,850 and I assume it's correct. 904 00:50:04,850 --> 00:50:06,350 I don't really know that much about 905 00:50:06,350 --> 00:50:08,750 iron distribution in humans. 906 00:50:08,750 --> 00:50:13,610 But they say the average adult has 3 or 4 grams of iron. 907 00:50:18,666 --> 00:50:21,800 You know, I sympathize with you guys for not 908 00:50:21,800 --> 00:50:23,420 being able to read my writing. 909 00:50:23,420 --> 00:50:25,460 When I write something now, half the time, 910 00:50:25,460 --> 00:50:26,880 I can't read it either. 911 00:50:26,880 --> 00:50:29,767 So when I was young, my writing was beautiful, 912 00:50:29,767 --> 00:50:31,100 and my board work was beautiful. 913 00:50:31,100 --> 00:50:34,580 And it's gone because we don't write that much anymore. 914 00:50:34,580 --> 00:50:37,580 So anyhow, iron distribution. 915 00:50:37,580 --> 00:50:40,940 We have 3 to 4 grams. 916 00:50:40,940 --> 00:50:44,240 And we'll see that, in contrast with cholesterol, 917 00:50:44,240 --> 00:50:46,880 where we take a lot in from the diet and then we have 918 00:50:46,880 --> 00:50:50,060 to regulate everything-- the biosynthesis of this, 919 00:50:50,060 --> 00:50:52,470 the uptake of all of this-- 920 00:50:52,470 --> 00:50:56,810 we don't take that much in from the diet, and almost nothing 921 00:50:56,810 --> 00:50:57,690 goes out of us. 922 00:50:57,690 --> 00:51:02,640 So it's really the iron is recycled in general. 923 00:51:02,640 --> 00:51:07,520 So this is really different from what we saw with cholesterol. 924 00:51:07,520 --> 00:51:13,130 And from this one book, the numbers are all about the same. 925 00:51:13,130 --> 00:51:14,240 So I think they're OK. 926 00:51:14,240 --> 00:51:17,595 Where would you expect to see the most iron? 927 00:51:17,595 --> 00:51:18,470 AUDIENCE: Hemoglobin. 928 00:51:18,470 --> 00:51:19,910 JOANNE STUBBE: Hemoglobin, yeah. 929 00:51:19,910 --> 00:51:26,360 And that's-- so hemoglobin, 2.6 grams. 930 00:51:26,360 --> 00:51:29,952 Where else would you expect to see iron? 931 00:51:29,952 --> 00:51:31,990 How about myoglobin? 932 00:51:31,990 --> 00:51:34,510 Myoglobin takes the oxygen from the hemoglobin 933 00:51:34,510 --> 00:51:37,690 and delivers it to the tissue. 934 00:51:37,690 --> 00:51:41,500 Remember, we talked a little about metal storage. 935 00:51:41,500 --> 00:51:43,850 So these are metal storage proteins. 936 00:51:43,850 --> 00:51:44,980 There's a gram there. 937 00:51:44,980 --> 00:51:48,730 That's going to be found in the liver. 938 00:51:48,730 --> 00:51:53,320 It turns out that only 4% of the iron 939 00:51:53,320 --> 00:51:58,540 is found in proteins that catalyze these many reactions. 940 00:51:58,540 --> 00:52:00,190 So next time, we'll come back. 941 00:52:00,190 --> 00:52:05,650 We'll have a big overview of iron in humans. 942 00:52:05,650 --> 00:52:09,580 And we will also talk about regulation 943 00:52:09,580 --> 00:52:12,230 at the translational level.