20β-Hydroxysteroid Dehydrogenase of Neonatal Pig Testis : Cofactor Requirement and Stereospecificity of Hydrogen Transfer from Nicotinamide Adenine Dinucleotide Phosphate, Reduced Form

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The cofactor requirement of purified 20β-hydroxysteroid dehydrogenase from cytosol fraction of neonatal pig testis, in the reduction of 17α-hydroxyprogesterone was investigated. The enzyme required β-nicotinamide adenine dinucleotide phosphate, reduced form (β-NADPH) as the preferred cofactor, with an apparent K_m value of 17 μM. Furthermore, α-nicotinamide adenine dinucleotide phosphate, reduced form (α-NADPH), β-3'-NADPH and B-nicotinamide adenine dinucleotide (β-NADH) were also utilized as hydrogen donors in the reduction at relatively high concentration with apparent K_m values of 85.2μM, 179.2μM and 1.00mM, respectively. The optimum pH was 5.5 when β-NADPH was used as the cofactor, while it was 6.0 when β-NADH was used. The hydrogen transfer from the β-NADPH to the product, 17α, 20β-dihydroxypregn-4-en-3-one catalyzed by 20β-hydroxysteroid dehydrogenase was stereospecific, and the 4-pro-S-hydrogen of the nicotinamide moiety was transferred to the product.
公益社団法人日本薬学会の論文
1989-01-25