Enzymatic redox chemistry: A proposed reaction pathway for the six-electron reduction of SO sub 3 sup 2 minus to S sup 2 minus by the assimilatory-type sulfite reductase from Desulfovibrio vulgaris (Hildenborough)

Journal Article · Tue Sep 10 00:00:00 EDT 1991 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00100a027· OSTI ID:5822859

Tan, Jian; Cowan, J A ^[1]

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1. Ohio State Univ., Columbus (United States)

A detailed reaction pathway for the six-electron reduction of SO{sub 3}{sup 2{minus}} to S{sup 2{minus}} by the assimilatory-type sulfite reductase (SiR) from Desulfovibrio vulgaris (Hildenborough) has been deduced from experiments with {sup 35}S-labeled enzyme and the relative reaction rates of nitrogenous substrates. The ligand bridging the prosthetic (Fe{sub 4}S{sub 4})-siroheme center is apparently exchanged by {sup 35}S{sup 2{minus}} in both oxidized and reduced enzyme. This {sup 35}S{sup 2{minus}} label was retained in the course of SO{sub 3}{sup 2{minus}} reduction, implicating substrate binding to the nonbridging axial site of the siroheme. A reaction mechanism is proposed in which SO{sub 3}{sup 2{minus}} binds to Fe{sup 2+} through the sulfur atom, followed by a series of two-electron reductive cleavages of S-O bonds. Protonation of oxygen facilitates bond cleavage, giving hydroxide as leaving group. The bridge remains intact throughout the course of the reaction, providing an efficient coupling pathway for electron transfer between the cluster and siroheme.

• OSTI ID: 5822859
• Journal Information: Biochemistry; (United States), Vol. 30:36; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
DESULFOVIBRIO
BIOLOGICAL PATHWAYS
OXIDOREDUCTASES
REDOX REACTIONS
ELECTRON TRANSFER
LIGANDS
SULFITES
SULFUR 35
BACTERIA
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMICAL REACTIONS
DAYS LIVING RADIOISOTOPES
ENZYMES
EVEN-ODD NUCLEI
ISOTOPES
LIGHT NUCLEI
MICROORGANISMS
NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PROTEINS
RADIOISOTOPES
SULFATE-REDUCING BACTERIA
SULFUR COMPOUNDS
SULFUR ISOTOPES
550200* - Biochemistry