Sulfate-reducing bacteria sulfite reductase

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]. 

Minz D., Flax J. L., Green S. J., Muyzer G., Cohen Y., Wagner M., Rittmann B. E., and Stahl D. A. (1999b) Diversity of sulfate-reducing bacteria in oxic and anoxic regions of a microbial mat characterized by comparative analysis of dissimilatory sulfite reductase genes. Appl. Environ. Microbiol. 65, 4666-4671. 

Kobayashi, K., Seki, Y. and Ishimoto,M., 1974. Biochemical studies on sulfate-reducing bacteria. XIII Sulfite reductase from Desulfovibrio vulgaris — mechanism of trithio-nate, thiosulfate and sulfide formation and enzymatic properties. J. Biochem., Tokyo, 75 519—529. 

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...

Kletzin A (1989) Coupled enzymatic production of sulfite, thiosulfite, and hydrogen sulfide from sulfur purification and properties of a sulfur oxygenase reductase from the facultative anaerobic archaebacterium Desulfurolobus ambivalens. J Bacteriol 171 1638-1643 Kobayashi K, Takahashi E, Ishimoto M (1972) Biochemical studies on sulfate reducing bacteria IX. Purification and some properties of sulfite reductase, desulfoviridin. J Biochem 72 879-887... 

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... 

In bacteria PAPS is a substrate for sulfate reduction. In plants, adenosine-5 -phosphosulfate is the substrate. Thioredoxin, a small thiol-containing protein, reduces the sulfate in PAPS to sulfite (SOS "). Sulfite is reduced by sulfite reductase in a six electron transfer through the intermediates NADPH, FAD, FMN, an iron-sulfur center, and the porphyrin siroheme. The end product is H2S. 

In Fig. 4.2, the oxidation mechanisms of lactate with sulfate in the bacteria of Desulfovibrio genus is shown. In the reduction of sulfate, first the compound is changed into adenylylsulfate (APS) using ATP. APS is reduced by the catalysis of adenylylsulfate reductase to sulfite and AMP. The sulfite formed is reduced to... 

The sulfite oxidase enzymes are widespread in Nature, and are found in plants, bacteria (the sulfite dehydrogenases) and in birds and mammals. In addition, this family also includes the assimilatory plant nitrate reductases, which have essentially similar molybdenum coordination and differ structurally in lacking an active site arginine that is present in sulfite oxidase, and in showing somewhat different active site structures on turnover. We will focus here on the animal sulfite oxidase enzymes, of which chicken and human are the best studied. In animals the enzyme is responsible for the physiologically essential oxidation of sulfite to sulfate. It is a dimer of 52 kDa subunits and resides in the mitochondrial inner-membrane space. Each monomer contains Mo associated with one molybdopterin, plus a cytochrome heme. The enzymes catalyze the following reaction, which occurs at the Mo site which is reduced from Mo(vi) to Mo(iv) in the process ... 

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