Sulfite-cytochrome c oxidoreductase

In Starkeya novella, sulfite is oxidized to sulfate by the catalysis of sulfite-cytochrome c oxidoreductase [reaction (4.5)]. The enzyme catalyzes the reduction with sulfite of not only native ferricytochrome c-550 but also horse ferricytochrome c and ferricyanide (Charles and Suzuki, 1966b Yamanaka et al., 1971, 1981b). The enzyme with a molecular mass of 40 kDa has a cytochrome c-551 subunit (23 kDa) (Yamanaka et al., 1981b) and molybdenum (Toghrol and Southerland, 1983). Recently, Kappler et al. (2000) has reported that the molecular mass of the enzyme is 46 kDa and has cytochrome c subunit of 8.8 kDa. 

Starkeya novella cytochrome c-550 was first partially purified by Charles and Suzuki (1966b), and thereafter highly purified by Yamanaka et al. (1971, 1991b). The cytochrome functions as the electron acceptor for sulfite-cytochrome c oxidoreductase as mentioned above, and as the electron donor for cytochrome c oxidase (Yamanaka and Fujii, 1980). It resembles mitochondrial cytochrome c in that it... 

In Paracoccus vertusus, thiosulfate is oxidized directly to sulfate by the catalysis of an enzyme complex containing several cytochromes c but not cytochrome b (Kelly, 1989). Although sulfite-cytochrome c oxidoreductase occurs in the enzyme complex, the enzyme is thought not to participate in the oxidation of thiosulfate, because the rhodanese activity is not observed with the complex. However, as already indicated, it could be that as the enzyme complex contains a thiosulfatecleaving enzyme strongly bound to both the sulfur-accepting protein and sulfite-cytochrome c oxidoreductase, thiosulfate appears to be oxidized directly to sulfate. 

Kappler U, Bennett B, Rethmeier J, Schwarz G, Deutzmann R, McEwan AG, Dahl C (2000) Sulfite cytochrome c oxidoreductase from Thiobacillus novellus. Purification, characterization, and molecular biology of a heterodimeric member of sulfite oxidase family. J Biol Chem 275 13202-13212... 

Lyric RM, Suzuki I (1970b) Enzymes involved in the metabolism of thiosulfate by Thiobacillus thioparus I. Survey of enzymes and properties of sulfite cytochrome c oxidoreductase. Can J Biochem 48 334-343... 

Lyric RM, Suzuki I (1970c) Kinetic studies of sulfite cytochrome c oxidoreductase, thiosulfate-oxidizing enzyme, and adenosine-5 -phosphosulfate reductase from Thiobacillus thioparus. Can J Microbiol 48 594-603... 

Sadler and Johnson [S96) claimed that reverse electron flow involving cytochrome c has not been established for T. neapolitanus and T. thio-parus and proposed the parallel pathways of Figs. 37a and 37b but offered no suggestion as to the source of the NADH. Yamanaka et al. (334) have found multiple cytochromes in T. novellus which they place in series as in Fig. 37c. They proposed that sulfite delivers its electrons to C551 by means of a sulfite. cytochrome c oxidoreductase enzyme. In all of these Thiobadllus species, there is at least one cytochrome c with a reduction potential near -j-280 mV and a molecular weight around 13,000, which probably is an evolutionary homolog of eukaryotic c. 

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...

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