[Reversible oxidation-reduction of NAD by hydrogen, catalyzed by soluble hydrogenase from Alcaligenes eutrophus Z-1].

The kinetics of NAD reduction by hydrogen, catalyzed by soluble hydrogenase from the hydrogen bacterium A. eutrophus Z-1 within a wide range of NAD substrate concentrations and pH were studied under aerobic and anaerobic conditions. The autocatalytic type of the reaction (with an induction period) and positive kinetic cooperativity with respect to NAD substrate at pH values greater than 8.0 were observed. A steady hydrogen release in a two-enzyme system involving hydrogenase, formiate dehydrogenase, formiate and NAD was demonstrated. A multistep pattern of the reaction mechanism of NAD reduction allowing to explain the autocatalytic type of NAD reduction by hydrogen as well as insensitivity of the reaction to air oxygen were proposed. Possible types of regulation of the soluble hydrogenase activity in the cell are discussed.