CATALYSIS OF THE OXIDATION OF NADH BY HETEROPOLYANIONS - A KINETIC-STUDY

The oxidation of NADH is readily obtained in the presence of Dawson-ty pe heteropolyanions (HPA). A stoichiometry of 2:1 is established for t he oxometalate/NADH couple. The starting system for electrochemistry s tudies consists of the one-electron reduction product of the heteropol yanions in the presence of various amounts of NADH. The quantitative s tudy by cyclic voltammetry confirms that the oxidized form of the sele cted HPAs are capable of catalyzing the oxidation of NADH. The kinetic s were studied quantitatively by double-step chronocoulometry. The log arithm of the second-order rate constant varies linearly with the E-0 of the first redox system of the HPAs with a slope of 16.4 V-1, indica ting that the oxidation of NADH proceeds by a multistep mechanism invo lving an initial rate-limiting one-electron transfer. The E degrees va lue for the NADH/NADH(.+) redox couple has been estimated. (C) Academi e des Sciences/Elsevier, Paris.