* To whom correspondence should be addressed.
Received July 6, 2006; Revision received October 11, 2006
The main catalytic properties of the Hox type hydrogenase isolated from the Gloeocapsa alpicola cells have been studied. The enzyme effectively catalyzes reactions of oxidation and evolution of H2 in the presence of methyl viologen (MV) and benzyl viologen (BV). The rates of these reactions in the interaction with the physiological electron donor/acceptor NADH/NAD+ are only 3-8% of the MV(BV)-dependent values. The enzyme interacts with NADP+ and NADPH, but is more specific to NAD+ and NADH. Purification of the hydrogenase was accompanied by destruction of its multimeric structure and the loss of ability to interact with pyridine nucleotides with retained activity of the hydrogenase component (HoxYH). To show the catalytic activity, the enzyme requires reductive activation, which occurs in the presence of H2, and NADH accelerates this process. The final hydrogenase activity depends on the redox potential of the activation medium (Eh). At pH 7.0, the enzyme activity in the MV-dependent oxidation of H2 increased with a decrease in Eh from -350 mV and reached the maximum at Eh of about -390 mV. However, the rate of H2 oxidation in the presence of NAD+ in the Eh range under study was virtually constant and equal to 7-8% of the maximal rate of H2 oxidation in the presence of MV.
KEY WORDS: cyanobacterium, Hox type hydrogenase, hydrogenase activity, diaphorase activity, reductive activation