Relationship between teh 3a- and 20β Hydroxysteroid.

Crystalline cortisone reductase prepared from Streptomyces hydrogenans has 3α- and 20βhydroxysteroid: NAD oxidoreductase activity. The total rate of reaction for mixtures of I7α,21dihydroxypregn-4-ene-3,11,20-trione with 5α-androstan-3,16-dione, and of 17β-hydroxy-lαmethyl-5α-androstan-3- one with either of these compounds indicated that these substrates do not react independently. 3β-Hydroxy-5α-androstan-16-one inhibited the reduction of both 17α,21dihydroxypregn-4-ene-3,11,20-trione and 5α-androstane-3,16-dione. 20β-Hydroxypregn-4-en-3-one also inhibited the reduction of both these substrates. The findings allow the view that the 3α- and 20β-activities may depend upon a aingle active centre with complex binding characteristics. [ABSTRACT FROM AUTHOR]