Sulfite: Cytochrome c Oxidoreductase from Thiobacillus novellus

Authors

Ulrike Kappler, Institut für Mikrobiologie und Biotechnologie
Brian Bennett, Marquette UniversityFollow
Jörg Rethmeier, Universität Bremen
Günter Schwarz, Technische Universität Braunschweig
Rainer Deutzmann, Institut für Mikrobiologie und Biotechnologie
Alistair G. McEwan, University of Queensland
Christiane Dahl, Institut für Mikrobiologie und Biotechnologie

Document Type

Article

Language

eng

Format of Original

11 p.

Publication Date

5-5-2000

Publisher

American Society for Biochemistry and Molecular Biology

Source Publication

Journal of Biological Chemistry

Source ISSN

0021-9258

Original Item ID

doi: 10.1074/jbc.275.18.13202

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 (EC1.8.2.1). Here we show that the enzyme from Thiobacillus novellus is a periplasmically located αβ 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 μm, 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.

Comments

Published version. Journal of Biological Chemistry, Vol. 275, No. 18 (May 5, 2000): 13202-13212. DOI. © 2000 by The American Society for Biochemistry and Molecular Biology, Inc. Used with permission.

Brian Bennett was affiliated with the CCLRC Daresbury Laboratory at the time of publication.

Recommended Citation

Kappler, Ulrike; Bennett, Brian; Rethmeier, Jörg; Schwarz, Günter; Deutzmann, Rainer; McEwan, Alistair G.; and Dahl, Christiane, "Sulfite: Cytochrome c Oxidoreductase from Thiobacillus novellus" (2000). Physics Faculty Research and Publications. 92.
https://epublications.marquette.edu/physics_fac/92