Chemical Modification of Catalytically Essential Functional Groups of NAD-Dependent Hydrogenase from Ralstonia eutropha H16

T. V. Tikhonova^1*, N. D. Savel'eva², and V. O. Popov¹

¹Bach Institute of Biochemistry, Russian Academy of Sciences, Leniniskii pr. 33, Moscow 119071, Russia; fax: (7-095) 952-0801; E-mail: ttikhonova@inbi.ras.ru

²Institute of Microbiology, Russian Academy of Sciences, pr. 60-letiya Oktyabrya 7/2, Moscow 117811, Russia; fax: (7-095) 135-6595; E-mail: ivanov@inmi.host.ru

^* To whom correspondence should be addressed.

Received September 17, 2002; Revision received October 25, 2002

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Amino acid residues His and Cys of the NAD-dependent hydrogenase from the hydrogen-oxidizing bacterium Ralstonia eutropha H16 were chemically modified with specific reagents. The modification of His residues of the nonactivated hydrogenase resulted in decrease in both hydrogenase and diaphorase activities of the enzyme. Activation of NADH hydrogenase under anaerobic conditions led to the modification of additional His residue (or residues) significant only for the hydrogenase activity. The rate of decrease in the diaphorase activity was unchanged. The modification of thiol groups of the nonactivated enzyme did not affect the activity of the hydrogenase. The effect of thiol-modifying agents on the activated hydrogenase was accompanied by inactivation of both diaphorase and hydrogenase activities. The modification degree and changes in the corresponding catalytic activities depended on conditions of the enzyme activation. Data on the modification of cysteine and histidine residues of the hydrogenase suggested that the enzyme activation should be associated with significant conformational changes in the protein globule.

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KEY WORDS: NAD-dependent hydrogenase from Ralstonia eutropha H16, chemical modification, hydrogenase activity, diaphorase activity

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