Theoretical analysis of eletrochemical reactions involving two successive one-electron transfers with dimerization of intermediate-applicaiton to NAD+/NADH redox couple

Abstract

The mechanism of an electrode reaction consisting of two successive one-electron (1e) transfer steps, coupled with dimerization of the intermediate product under conditions of steady-state convective diffusion, has been theoretically analyzed for the situation where the second electron-transfer step is accompanied or preceded by protonation of the intermediate product. The resulting relationship have been used to examine the electrochemical behavior of the biologically important NAD+/NADH redox couple. The model, which seems best to fit the experimental data involves: (a) 1e reduction NAD+ to NAD, which can dimerize, followed at more negative potential by concerted protonation and 1e reduction of NAD to NADH, where the proton donor is an HB species such as H3O+ or NH4+; (b) an apparently single-step 2e oxidation of NADH to NAD+. Possible causes for the differences in electrochemical NAD+ reduction and NADH oxidation are considered in terms of the implications of theory.