11/3-Hydroxy steroid dehydrogenase preparation

A 3a-hydroxysteroid dehydrogenase active on 7a-hydroxy-5 -cholestan-3-one and 7a,12a-dihydroxy-5 -cholestan-3-one (cf. Fig. 3), was partially purified (about 300-fold) from rat Uver cytosol by Berseus [112,113]. NADPH was required as cofactor and hardly any activity was observed with NADH. The preparation was also active towards 3-oxo steroids of the Cjg, C21 and C24 series, and in these cases appreciable activity was obtained also with NADH. The mechanism of reduction involves a stereospecific transfer of a hydride ion from the 4A position of NADPH to the 3)S position of the steroid [114],... 

The reduction of a 3-oxosteroid, catalyzed by 3a-hydroxysteroid dehydrogenase from rat liver, has been shown to involve transfer of a hydride ion from the A-side of NADPH to the 3j -position of the steroid (44,52). The oxidation of 4-cholestene-3a,7a-diol into 7a-hydroxy-4-cholesten-3-one, catalyzed by the same enzyme preparation, has also been shown to involve the A-side of NADPH (52). It remains to be established whether or not Zl -3a-hydroxysteroid dehydrogenase activity is due to enzyme(s) different from 3a-hydroxysteroid dehydrogenase(s). 

Purified preparations of rat liver Sa-hydimgrsteroid dehydrogenase catalyze the ready interconversion of 3a-hydroxy-3-ketosteroids, DPN being the H-carrier the steroids were active at 10 M (Hurlock and Talalay, 1958). Since DPN and TPN are interconvertible, a redox coupling is theoretically possible between pteridines and these steroids. 

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