A mechanistic and electrochemical study of the interaction between dimethyl sulfide dehydrogenase and its electron transfer partner cytochrome c2

  • Nicole L. Creevey
  • Alastair G. McEwan
  • Paul V. Bernhardt
Original Paper

DOI: 10.1007/s00775-008-0406-3

Cite this article as:
Creevey, N.L., McEwan, A.G. & Bernhardt, P.V. J Biol Inorg Chem (2008) 13: 1231. doi:10.1007/s00775-008-0406-3

Abstract

Dimethyl sulfide dehydrogenase isolated from the photosynthetic bacterium Rhodovulum sulfidophilum is a heterotrimeric enzyme containing a molybdenum cofactor at its catalytic site, as well as five iron–sulfur clusters and a heme b cofactor. It oxidizes dimethyl sulfide (DMS) to dimethyl sulfoxide in its native role and transfers electrons to the photochemical reaction center. There is genetic evidence that cytochrome c2 mediates this process, and the steady state kinetics experiments reported here demonstrated that cytochrome c2 accepts electrons from DMS dehydrogenase. At saturating concentrations of both substrate (DMS) and cosubstrate (cytochrome c2), Michaelis constants, KM,DMS and KM,cyt of 53 and 21 μM, respectively, were determined at pH 8. Further kinetic analysis revealed a “ping-pong” enzyme reaction mechanism for DMS dehydrogenase with its two reactants. Direct cyclic voltammetry of cytochrome c2 immobilized within a polymer film cast on a glassy carbon electrode revealed a reversible FeIII/II couple at +328 mV versus the normal hydrogen electrode at pH 8. The FeIII/II redox potential exhibited only minor pH dependence. In the presence of DMS dehydrogenase and DMS, the peak-shaped voltammogram of cytochrome c2 is transformed into a sigmoidal curve consistent with a steady-state (catalytic) reaction. The cytochrome c2 effectively mediates electron transfer between the electrode and DMS dehydrogenase during turnover and a significantly lower apparent electrochemical Michaelis constant \( K_{{{\text{M,DMS}}}}^{\prime } \) of 13(±1) μM was obtained. The pH optimum for catalytic DMS oxidation by DMS dehydrogenase with cytochrome c2 as the electron acceptor was found to be approximately 8.3.

Keywords

Cytochrome Molybdenum Oxidoreductase Voltammetry 

Abbreviations

DCPIP

2,6-Dichlorophenolindophenol

DMS

Dimethyl sulfide

DMSO

Dimethyl sulfoxide

NHE

Normal hydrogen electrode

Tris

Tris(hydroxymethyl)methanamine

Copyright information

© SBIC 2008

Authors and Affiliations

  • Nicole L. Creevey
    • 1
  • Alastair G. McEwan
    • 1
  • Paul V. Bernhardt
    • 1
  1. 1.Centre for Metals in Biology, School of Molecular and Microbial SciencesUniversity of QueenslandBrisbaneAustralia

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