20-BETA-HYDROXYSTEROID DEHYDROGENASE OF NEONATAL PIG TESTIS - 3-ALPHA/BETA-HYDROXYSTEROID DEHYDROGENASE-ACTIVITIES CATALYZED BY HIGHLY PURIFIED ENZYME

Pig testicular 20-beta-hydroxysteroid dehydrogenase (20-beta-HSD) has also 3-alpha- and 3-beta-HSD (3-alpha/beta-HSD) activities. The purified 20-beta-HSD preparation from neonatal pig testes could catalyze the conversion of 5-alpha-dihydrotestosterone (5-alpha-DHT) in the presence of beta-NADPH to 5-alpha-androstane-3-alpha, 17-beta-diol and 5-alpha-androstane-3-beta, 17-beta-diol at the ratio of 4:3, and the specific 3-alpha/beta-HSD activity of 20-beta-HSD for 5-alpha-DHT was about 10 or 15 times larger than the 20-beta-HSD activities for 17-alpha-hydroxypregn-4-ene-3,20-dione (17-alpha-hydroxyprogesterone) or progesterone, respectively. The result indicates that the testicular 20-beta-HSD has high 3-alpha(axial, 3R)- and 3-beta(equatorial, 3S)-HSD activity. The testicular 20-beta-HSD could catalyze the reversible conversion of various 5-alpha- or 5-beta-dihydrosteroids which have a 3-carbonyl or 3-hydroxyl group with beta-NADP(H) as the preferred cofactor. The enzyme transferred the 4-proS hydrogen of NADPH to the 5-alpha-DHT for both 3-alpha- and 3-beta-hydroxylation and it was the same as the 20-beta-hydroxylation of 17-alpha-hydroxyprogesterone. Although the 3-alpha/beta-HSD activity has been known to be present in 3-alpha,20-beta-HSD of Streptomyces hydrogenans, the enzymological properties for 3-alpha/beta-HSD activity catalyzed by testicular 20-beta-HSD were different from the properties for 3-alpha/beta-HSD activity catalyzed by prokaryotic 3-alpha,20-beta-HSD with respect to the specificity of the catalytic reaction and the cofactor requirement.