Pasteurianum 32 and d vulgaris 33 have been

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pasteurianum 32 and D. vulgaris 33 have been determined. 33a The C. pasteurianum protein structure is known to a resolution of 1.2 A, placing it among the metalloproteins whose structures are known with greatest precision. The individual Fe and S atoms are clearly resolvable. As shown in Figure 7.4, the single iron is coordinated by four S ligands provided by Cys-6, Cys-9, Cys-39, and Cys-42. The sequence Cys-x-y-Cys is a common one in Fe-S proteins, because it allows both cysteine residues to bind to the same metal site or cluster. The Fe-S distances and angles
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Table 7.1 Properties of some iron-sulfur proteins. Molecular Redox weight Fe-S potential EPR Protein source (subunits) composition mY (pH) g values References Rubredoxins Clostridium pasteurianum 6,000 Fe - 58 (7) 9.3 4.3 26 Pseudomonas oleovorans 6,000 Fe 9.42 0.9 1.25 a 44 4.02 4.77 4.31 Fe2S2 proteins Spinach ferredoxin 11,000 [2Fe-2S] 420 (7.0) 2.05 1.96 1.89 350, 351 Parsley ferredoxin 11,000 [2Fe-2S] 2.05 1.96 1.90 352 Euglena ferredoxin 11,000 [2Fe-2S] 2.06 1.96 1.89 352 Adrenal cortex ferredoxin (pig) 16,000 [2Fe-2S] -270 (7.0) 2.02 1.93 1.93 352,353 [Adrenodoxin] Pseudomonas putida ferredoxin 12,500 [2Fe-2S] -240 (7.0) 2.02 1.93 1.93 352, 353 [Putidaredoxin] Clostridium pasteurianum 25,000 [2Fe-2S] - 300 (7.5) 2.00 1.96 1.94 354 Xanthine Oxidase 280,000 (2) 2 x [2Fe-2S] I - 343 (8.2) 2.02 1.94 1.90 355, 356 II - 303 (8.2) 2.12 2.01 1.91 Thermus thermophilus Rieske 20,000 2 x [2Fe-2S] + 150 (7.8) 2.02 1.90 1.80 93,357 Fe4S4 proteins Clostridium pasteurianum 6,000 2 x [4Fe-4S] 420 (8.2) 2.06 1.92 1.89 b 115 Bacillus stearothermophilus 9,100 [4Fe-4S] -280 (8.0) 2.06 1.92 1.89 358 Desulfovibrio gigas ferredoxin I 18,000 (3) [4Fe-4S] -455 (8.0) 2.07 1.94 1.92 359 Aconitase (beef heart) [active] 81,000 [4Fe-4S] 2.06 1.93 1.86 Chromatium vinosum HiPIP 10,000 [4Fe-4S] + 356 (7.0) 2.12 2.04 2.04 353 Paracoccus sp. 10,000 [4Fe-4S] + 282 (7.0) 353
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Azotobacter vinlandii Fd I 14,500 [3Fe-4S] [4Fe-4S] 645 (8.3) 2.06 1.93 1.89 c 360 Thermus aquaticus 10,500 [3Fe-4S] [4Fe-4S] -550 (9.0) 2.06 1.93 l.92 c 353, 361 Fe3S4 proteins Desulfovibrio gigas Fd II 6,000 (4) [3Fe-4S] 130 (8.0) 2.02 359 Azotobacter vinlandii Fd I 14,500 [3Fe-4S] 450 (8.3) 2.01 360 [4Fe-4S] Thermus aquaticus 10,500 [3Fe-4S] 260 (9.0) 2.02 1.99 1.94 d 353, 361 [4Fe-4S] Aconitase (beef heart) [inactive] 81,000 [3Fe-4S] 2.01 a g'-tensors for ± ! and ±~ Kramers doublets, respectively, of the 5 = ~ system. The values of 0.9 and 1.25 are calculated (not observed) 44 b The fully reduced protein has a complex spectrum due to magnetic coupling between the two identical Fe4S4 clusters. The g-values are those for partly reduced samples, and represent a magnetically isolated cluster. c The reported spectrum is complex because of magnetic interaction with the reduced Fe3S4 cluster. d Recent evidence suggests that Thermus thermophilus and Thermus aquaticus are actually the same species. 362 EPR parameters of the homologous Thermus thermophilus ferredoxin estimated from computer simulations. 361 In this protein a signal originating from the Fe3S4 cluster at g' = 12, attributable to f).M, = ± 4 transitions, is observed for the reduced (5 = 2) cluster. [371]
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372 7 I FERREDOXINS, HYDROGENASES, AND NITROGENASES: METAL-SULFIDE PROTEINS Figure 7.4 The x-ray crystal structure of rubredoxin from Clostridium pasteurianum.
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