Sulfate-reducing bacteria, cytochrome

Michel, C., Brugna, M., Aubert, C., Bernadac, A. and Bruschi, M., Enzymatic reduction of chromate comparative studies using sulfate-reducing bacteria. Key role of polyheme cytochroms c and hydro-genases. Appl. Microbiol. Biotechnol., 55, 95-100, 2001. 

Although electron transfers in biological systems are generally expected to be non-adiabatic, it is possible for some intramolecular transfers to be close to the adiabatic limit, particularly in proteins where several redox centers are held in a very compact arrangement. This situation is found for example in cytochromes C3 of sulfate-reducing bacteria which contain four hemes in a 13 kDa molecule [10, 11], or in Escherichia coli sulfite reductase where the distance between the siroheme iron and the closest iron of a 4Fe-4S cluster is only 4.4 A [12]. It is interesting to note that a very fast intramolecular transfer rate of about 10 s was inferred from resonance Raman experiments performed in Desulfovibrio vulgaris Miyazaki cytochrome Cj [13]. 

Barton LL, editor. 1995. Sulfate-reducing bacteria. New York Plenum Press. Blanchard L, Marion D, Pollock B, et al. 1993. Overexpression of Desulfovibrio vulgaris Hildenborough cytochrome C553 in Desulfovibrio desulfuricans G200 evidence of conformational heterogeneity in the oxidized protein by NMR. Eur J Biochem 218 293-301. 

Several proteins were reported to function as enzymes for the dissimilatory reduction of metals and nonessential elements. As Usted in Table 16.4, the most frequently reported proteins involved in metal reduction are the cytochromes from sulfate-reducing bacteria. The focus on these cytochromes supports the initial papers by Lovley and colleagues in which they reported that reduced cytochrome Cs from Desulfovibrio vulgaris Hildenborough reduces uranyl salts (Lovley et al. 1993a) and chromate (Lovley and PhUhps 1994). 

As reviewed by Lojou et al. (1998a, 1998b), cytochrome (cyt) C3 and cyt Cl from the sulfate-reducing bacteria are effective in reducing metals. The... 

Not all cytochromes from sulfate-reducing bacteria reduce Fe(III) or other metals. D. vulgaris produces a cyt C553, which has a molecular mass of 9 kDa, midpoint redox potential of OmV, and a single heme and the iron atom is coordinated by histidine methionine. It is unclear at this time if the inability of this cyt C553 to reduce metals is due to lack of a bishistidinyl iron coordination or to some other factor, such as steric hinderance owing to orientation of heme in the protein. 

The reduction of U(VI) by sulfate-reducing bacteria appears to occur at the cell surface of the anaerobes, since the reduced products of these elements accumulates in the environment outside of the cell. The proteins of cyt Cs and cyt c have been demonstrated to function as nonspecific metal dehydrogenases however, these cytochromes are found in the periplasm and not in the outer membrane. Thus, if it were analogous to Fe(III) reduction, uranyl ions would most appropriately be reduced by a cytochrome in the outer membrane of the sulfate reducers. As demonstrated by Laishley and Bryant (see Chapter 18) cytochromes are located in the outer membrane of certain sulfate reducers however, their role in reduction of U(VI) remains to be demonstrated. 

Fig. 4.2. The oxidation mechanisms of lactate by sulfate in the sulfate-reducing bacteria of Desulfovibrio genus. Circled numbers 1, lactate dehydrogenase (cytochrome c-553) 2, pyruvate-ferredoxin 2-oxidoreductase (CoA-acetylating) 3, phosphate acetyltransferase 4, acetate kinase 5, sulfate adenylyltransferase 6, adenylylsulfate reductase 7, sulfite reductase 8, adenylate kinase. ATP adenosine 5 -triphosphate is also biosynthesized by the catalysis of ATP synthase using the energy liberated by the electron transfer around this part...

Cytochrome c3 is characteristic of the sulfate-reducing bacteria. The cytochrome has four heme C molecules in the molecule (13 kDa) (Yagi and Maruyama, 1971). Both the 5th and 6th axial ligands of the four heme C molecules in the cytochrome are histidine residues at pH 6.0(Higuchi et al., 1981). The midpoint redox potentials at pH 7.0 of the four heme molecules vary with the heme ranging from... 

In the sulfate-reducing bacteria there is another cytochrome which resembles cytochrome c3 in the spectral properties and redox potential but differs from this cytochrome in molecular mass this is cytochrome c3 (26 kDa) which has eight heme C molecules in the molecule. The cytochrome molecule is composed of two polypeptides of 13 kDa (Loufti et al., 1989). On the basis of the amino acid sequence, however, the 13 kDa polypeptide differs from cytochrome c3 (Guer-lesquin et al., 1982 LeGall and Peck, 1987 Loufti et al., 1989). Desulfovibrio gigas cytochrome c3 (26 kDa) molecule is composed of two 13 kDa molecules bound to each other by an S-S bond (Bruschi et al., 1996). It is claimed that cytochrome c3 (26 kDa) is very effective as the electron donor for thiosulfate reductase (Hat-chikian et al., 1972). 

Little is known about elemental sulfur reductase of the sulfur respiration system, though cytochrome c3 of the sulfate-reducing bacteria has been reported to reduce... 

Fauque G, Herve D, LeGall J (1979) Structure-function relationship in hemoproteins the role of cytochrome c3 in the reduction of colloidal sulfur by sulfate-reducing bacteria. Arch Microbiol 121 261-264... 

Ishimoto M, Koyama J, Nagai Y (1954) Biochemical studies on sulfate-reducing bacteria IV. The cytochrome system of sulfate-reducing bacteria. J Biochem 41 763-770 Ivanovsky RN, Krasilnikova EN, Fal YI (1993) A pathway of the autotrophic C02 fixation in Chloroflexus aurantiacus. Arch Microbiol 159 257-264 Iverson TM, Arciero DM, Hooper AB, Rees DC (2001) High solution structures of the oxidized and reduced states of cytochrome c-554 from Nitrosomonas europaea. J Biol Inorg Chem 6 390-397... 

Steuber J, Cypionk H, Kroneck PMH (1994) Mechanism of dissimilatory sulfite reduction by Desulfovibrio desulfuricans purification of membrane-bound sulfite reductase and coupling with cytochrome c3 and hydrogenase. Arch Microbiol 162 255-260 Stille W, Triiper HG (1984) Adenylylsulfate reductase in some new sulfate reducing bacteria. Arch Microbiol 137 145-150... 

A diheme cytochrome has been isolated from one species of sulfate-reducing bacteria, Desulfovibrio desulfuricans ATCC 27774 [92]. It has been named as the Split-Soret cytochrome as it displays a shoulder at 415 nm for the Soret band of the reduced form. It is a dimer of a 26 kDa subunit, each containing two hemes c. The function of this cytochrome has not been elucidated and it was observed that it is present in cells grown both on nitrate or sulfate. A diheme cytochrome of 11 kDa was isolated from Wolinella succinogenes, but the low yield of purified protein prevented detailed structural studies [38]. 

Finally, Class III cytochromes c, also called cytochromes C3, contain four hemes, each ligated by two axial histidines. These proteins are found in a restricted class of sulfate-reducing bacteria and may be associated with the cytoplasmic membrane. The low molecular weights of cytochromes Cj ( 14.7 kDa) require that the four hemes be much more exposed to the solvent than the hemes of other cytochromes (see Figure 6.9), which may be in part responsible for their unusually negative ( — 200 to —350 mV) reduction potentials. These proteins possess many aromatic residues and short heme-heme distances, two properties that could be responsible for their anomalously large solid-state electrical conductivity. " ... 

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