The first non-turnover voltammetric response from a molybdenum enzyme: direct electrochemistry of dimethylsulfoxide reductase from Rhodobacter capsulatus.
The first direct voltammetric response from a molybdenum enzyme under non-turnover conditions is reported. Cyclic voltammetry of dimethylsulfoxide reductase from Rhodobacter capsulatus reveals a reversible Mo(VI/V) response at +161 mV followed by a reversible Mo(V/IV) response at -102 mV versus NHE at pH 8. The higher potential couple exhibits a pH dependence consistent with protonation upon reduction to the Mo(V) state and we have determined the p K(a) for this semi-reduced species to be 9.0. The lower potential couple is pH independent within the range 5<pH<10. The optical spectrum of the Mo chromophore has been investigated with spectroelectrochemistry. At high potential, in its resting state, the enzyme exhibits a spectrum characteristic of the Mo(VI) form. This changes significantly following bulk electrolysis (-400 mV versus NHE) at an optically transparent, indium-doped tin oxide working electrode, where a single visible electronic maximum at 632 nm is observed, which is comparable with spectra reported previously for the dithionite-reduced enzyme. This two-electron process is chemically reversible by reoxidizing the enzyme at the electrode in the absence of mediators or promoters. The activity of the enzyme has been established by observation of a catalytic current in the presence of DMSO at pH 8, where a sigmoidal (steady state) voltammogram is seen.
Aguey-Zinsou
Kondo-François
KF
Department of Chemistry, University of Queensland, Brisbane, 4072, Australia.
Bernhardt
Paul V
PV
McEwan
Alastair G
AG
Ridge
Justin P
JP
D004563:Electrochemistry; D004566:Electrodes; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007506:Iron-Sulfur Proteins; D008982:Molybdenum / Q000737:chemistry*; D010088:Oxidoreductases / Q000737:chemistry*; D016354:Rhodobacter capsulatus / Q000201:enzymology*; D013056:Spectrophotometry, Ultraviolet
D007202:Indicators and Reagents; D007506:Iron-Sulfur Proteins; D008982:Molybdenum; D010088:Oxidoreductases; C045664:dimethyl sulfoxide reductase