Optimization of the mediated electrocatalytic reduction of NAD(+) by cyclic voltammetry and construction of electrochemically driven enzyme bioreactor

The optimal concentrations of diaphorase, methyl viologen (MV2+) and NAD(+) in the mediated electrocatalytic reduction of NAD(+) were decided by apply ing cyclic voltammetry. The steady-state catalytic current was achieved und er the conditions of 1.5 U diaphorase ml(-1), 0.2 mM MV2+, and 4.8 mM NAD() at the scan rate of 2 mV s(-1), suggesting that the rate of the electroca talytic reaction is the highest under the former conditions. However, NAD() was effective at 0.3 mM as it was at 4.8 mM when the electrocatalysis is coupled with an enzymatic synthesis requiring NADH. In effect, the electroc hemical procedure under the conditions of 1.5 U diaphorase ml(-1), 0.2 mM M V2+, and 0.3 mM NAD(+) worked satisfactorily to drive an enzymatic reductio n of pyruvate to D-lactate in the presence of D-lactate dehydrogenase.