Cytochrome P450 (P450) enzymes typically require the presence of at least cytochrome P450 reductase (CPR) and NADPH to carry out the metabolism of xenobiotics. To address whether the need for redox transfer proteins and the NADPH cofactor protein could be obviated, CYP2C9 was bonded to a gold electrode through an 11-mercaptoundecanoic acid and octanethiol self-assembled monolayer (SAM) through which a current could be applied. Cyclic voltammetry demonstrated direct electrochemistry of the CYP2C9 enzyme bonded to the electrode and fast electron transfer between the heme iron and the gold electrode. To determine whether this system could metabolize warfarin analogous to microsomal or expressed enzyme systems containing CYP2C9, warfarin was incubated with the CYP2C9-SAM-gold electrode and a controlled potential was applied. The expected 7-hydroxywarfarin metabolite was observed, analogous to expressed CYP2C9 systems, wherein this is the predominant metabolite. Current-concentration data generated with increasing concentrations of warfarin were used to determine the Michaelis-Menten constant (K(m)) for the hydroxylation of warfarin (3 microM), which is in good agreement with previous literature regarding K(m) values for this reaction. In summary, the CYP2C9-SAM-gold electrode system was able to carry out the metabolism of warfarin only after application of an electrical potential, but in the absence of either CPR or NADPH. Furthermore, this system may provide a unique platform for both studying P450 enzyme electrochemistry and as a bioreactor to produce metabolites without the need for expensive redox transfer proteins and cofactors.