COUPLING OF THE ELECTROENZYMATIC REDUCTION OF NAD(+) WITH A SYNTHESISREACTION

Hydrogenase from Alcaligenes eutrophus H16 (E.C. 1.12.1.2) catalyzes t he electrochemical reduction of the pyridine cofactor NAD(+). Previous studies emphasized the kinetics and thermodynamics of the reaction. W e applied hydrogenase to regenerate NADH for the transformation of alp ha-ketoglutarate into L-glutamate catalyzed by an L-glutamate dehydrog enase. The system was first studied in an electrochemical thin-layer c ell. A turnover number (TN) of 450 h(-1) was obtained The influence of the ratio of L-glutamate dehydrogenase and hydrogenase activities is discussed. The separate analyses of the glutamate dehydrogenase cataly sis on the one hand and the hydrogenase electrocatalysis on the other led to the hypothesis that the behavior of the coupled process was con trolled by the NADH concentration level. We exploited the qualitative conclusions drawn from the analytical study to test the process on a p reparative scale-batch reactor. A TN of 207 h(-1) was reached. The poo r stability of the hydrogenase was the major hindrance to the developm ent of the reactor, but a possible solution was discussed by means of the stabilizing effect of the electrochemical conditions.