Faculty Collaboration Database

Sulfite:Cytochrome c oxidoreductase from Thiobacillus novellus. Purification, characterization, and molecular biology of a heterodimeric member of the sulfite oxidase family. J Biol Chem 2000 May 05;275(18):13202-12

Date

05/02/2000

Pubmed ID

10788424

DOI

10.1074/jbc.275.18.13202

Scopus ID

2-s2.0-0034607799 (requires institutional sign-in at Scopus site)   157 Citations

Abstract

Direct oxidation of sulfite to sulfate occurs in various photo- and chemotrophic sulfur oxidizing microorganisms as the final step in the oxidation of reduced sulfur compounds and is catalyzed by sulfite:cytochrome c oxidoreductase (EC ). Here we show that the enzyme from Thiobacillus novellus is a periplasmically located alphabeta heterodimer, consisting of a 40.6-kDa subunit containing a molybdenum cofactor and an 8.8-kDa mono-heme cytochrome c(552) subunit (midpoint redox potential, E(m8.0) = +280 mV). The organic component of the molybdenum cofactor was identified as molybdopterin contained in a 1:1 ratio to the Mo content of the enzyme. Electron paramagnetic resonance spectroscopy revealed the presence of a sulfite-inducible Mo(V) signal characteristic of sulfite:acceptor oxidoreductases. However, pH-dependent changes in the electron paramagnetic resonance signal were not detected. Kinetic studies showed that the enzyme exhibits a ping-pong mechanism involving two reactive sites. K(m) values for sulfite and cytochrome c(550) were determined to be 27 and 4 micrometer, respectively; the enzyme was found to be reversibly inhibited by sulfate and various buffer ions. The sorAB genes, which encode the enzyme, appear to form an operon, which is preceded by a putative extracytoplasmic function-type promoter and contains a hairpin loop termination structure downstream of sorB. While SorA exhibits significant similarities to known sequences of eukaryotic and bacterial sulfite:acceptor oxidoreductases, SorB does not appear to be closely related to any known c-type cytochromes.

Author List

Kappler U, Bennett B, Rethmeier J, Schwarz G, Deutzmann R, McEwan AG, Dahl C

Author

Brian Bennett D.Phil. Professor and Chair in the Physics department at Marquette University

MESH terms used to index this publication - Major topics in bold

Amino Acid Sequence
Bacterial Proteins
Base Sequence
Cytochrome Reductases
Molecular Sequence Data
Sequence Alignment
Substrate Specificity
Sulfite Dehydrogenase
Thiobacillus