Steroid-Protein Interaction : Substrate Specificity of 20β-Hydroxysteroid Dehydrogenase

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The reactivities of 20β-hydroxysteroid dehydrogenase [EC 1.1.1.53] from Streptomyces hydrogenans towards 64 kinds of steroids having the pregnan-20-one skeleton were investigated. The presence and nature of a substituent around the reacting 20-oxo group of the steroid played a decisive role in the interaction with the catalytic site of the enzyme. In general, steroids having bulky group (s) at C-21 and/or C-17 did not act as substrates, though steroids having a bulky group at C-3 or C-11 were utilized by the enzyme. The existence of a substituent at C-16 caused 20-oxo steroids to lose their reactivity almost completely, but the existence of a substituent at C-3,C-6,C-9,C-11,C-17 or C-21 did not. The configurational relationship between the plane of the steroid ring and the C-17 side chain might also be important in steroid recognition by the enzyme. Among the nonsubstrate steroids, 16β-methylpregn-4-ene-3,20-dione was a competitive inhibitor with respect to both steroid substrate and coenzyme. It was inferred that the steroid ring of the inhibitor molecule competed with the substrate binding process, while the 16β-methyl substituent competed with the coenzyme action. When 16α-methylpregn-4-ene-3,20-dione, pregn-4-ene-3,20-dione and 17,21-dihydroxypregn-4-ene-3,11,20-trione were used as substrates, the apparent K_m values for NADH were 13.97,3.91 and 4.07μM, respectively. The presence of a substituent at C-16 unfavorably affected the apparent K_m for NADH, but substituents at C-21,C-17 or C-11 did not. These results suggest that the coenzyme may be located in the vicinity of C-16 of the steroid molecule in the ternary complex, steroid-coenzyme-enzyme.
公益社団法人日本薬学会の論文
1980-02-25

Steroid-Protein Interaction : Substrate Specificity of 20β-Hydroxysteroid Dehydrogenase

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