Carbethoxylation and pH Profiles of Kinetic Parameters of 20β-Hydroxysteroid Dehydrogenase from Streptomyces hydrogenans

概要

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20β-Hydroxysteroid dehydrogenase from Streptomyces hydrogenans is inactivated by diethylpyrocarbonate. It was shown by spectrophotometric studies that two histidine residues per molecule of the enzyme are necessary for enzyme activity. The involvement of histidine residues in the enzyme activity is also indicated by the pH dependence of kinetic parameters for NADH, which shows an inflection point at pH 6.4. The carbethoxyhistidine residues in the modified enzyme are slowly hydrolyzed and the enzyme activity is recovered, but this reactivation is suppressed by addition of NADH. The inactivation of the enzyme by diethylpyrocarbonate is largely prevented by reduced coenzymes, though the steroid substrates alone have no protective effects. It is presumed from kinetic data that carbethoxylation of 20β-hydroxysteroid dehydrogenase does not affect the affinity of the enzyme for NADH. These findings suggest that some histidine residues participate in the enzyme activity and that these histidine residues are located near but not at the coenzyme binding site of the enzyme.
公益社団法人日本薬学会の論文
1982-08-25