1991 年 39 巻 4 号 p. 972-975
Neonatal pig testicular 20β-hydroxysteroid dehydrogenase (20β-HSD) catalyzed the oxidation of 20β-hydroxysteroids, 17α, 20β-dihydroxypregn-4-en-3-one and 20β-hydroxypregn-4-en-3-one in the presence of β-nicotinamide adenine dinucleotide phosphate (β-NADP+). The behavior of 20β-HSD activity toward the substrate of 17α, 20β-dihydroxypregn-4-en-3-one differed from the catalytic reaction for 20β-hydroxypregn-4-en-3-one. The enzyme could catalyze not only 20β-hydroxysteroids but also 20α-hydroxy-5-ene steroids, 20α-hydroxypregn-5-en-3β-ol and 17α, 20α-hydroxypregn-5-en-3β-ol with 22.1 and 8.7% of activity relative to 20β-hydroxypregn-4-en-3-one, respectively. The enzyme preferentially required β-NADP+, and also utilized β-nicotinamide adenine dinucleotide β-NAD+ and β-nicotinamide adenine dinucleotide 3'-phosphate (β-3'-NADP+) nonspecifically as the cofactor. The optimum pH was observed at pH 7.5 with the substrate of 20β-hydroxypregn-4-en-3-one. The activation energies obtained from oxidation-reduction reactions of 20β-HSD for the substrate of 20β-hydroxypregn-4-en-3-one, progesterone and 17α-hydroxyprogesterone were estimated at 13.8, 27.0 and 2.0 kcal/mol, respectively.
