Effects of pH on the Maximal Rates of Reactions Catalyzed by NAD-Dependent Hydrogenase from Alcaligenes eutrophus

T. V. Tikhonova,¹ A. Yu. Kirsanov,¹ and V. O. Popov^1,2

¹Bakh Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 117071 Russia; fax: (095) 952-0801; E-mail: vpopov@glas.apc.org

²To whom correspondence should be addressed.

Submitted January 24, 1997; revision submitted July 17, 1997.

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The effects of pH on the maximal rates of the hydrogenase and diaphorase reactions with various acceptors catalyzed by NAD-dependent hydrogenase from Alcaligenes eutrophus H16 were studied. The data indicate that at all pH values, the electron transfer to the acceptor is the rate-limiting stage; hence, the reaction rate is essentially determined by the redox properties of the second substrate. The role of the slow conformational changes associated with hydrogenase activation is important for the patterns of pH profiles of the catalytic activities of the enzyme.

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KEY WORDS: NAD-dependent hydrogenase from Alcaligenes eutrophus, effect of pH, maximal rate, activation.

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