Abstract
Male hamster kidney cytosol exhibited strong 5β-reductase activity. Incubation of cytosol with [4- 14C]-testosterone at pH 6.7 yielded 5β-DHT with minor quantities of 5β-androstane-3α,17β-diol and 5β-androstane-3β,17β-diol. Incubation with [4- 14C]-androstendione yielded 5β-androstanedione and smaller quantities of testosterone, 5β-DHT, 3α-hydroxy-5β-androstan-17-one, 3β-hydroxy-5β-androstan-17-one and 5β-androstane-3α,17β-diol. The two major metabolites were progressively increased with increase in the concentration of the respective substrates but the other metabolites showed very little change. The metabolism of the respective substrates was progressively decreased with changes in pH of the incubation mixture from 6.0–7.5 accompanied by a parallel decrease in the formation of the respective major metabolites. NADPH was much more effective than NADH as coenzyme. The microsomes exhibited a trace of 5β-reductase activity only with NADPH and androstenedione. The kidney homogenate at pH 10.1 effectively converted [4- 14C]-testosterone to [4- 14C]-androstenedione. The dehydrogenase activity was present in the cytosol and microsomes. NAD + was more effective than NADP + in the cytosol and the reverse was indicated for the microsomes. Spectrophotometric assay revealed not only NADP +-linked Hβ-dehydrogenase activity but also a lower 3α-dehydrogenase activity but no detectable 3β- or 17α-dehydrogenase activity. NAD +-linked activity was not explored because of the interference by the very high endogenous NAD +-reduetase activity.
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