Studies of the Human Testis. XIII. Properties of Nicotinamide Adenine Dinucleotide (Reduced Form) linked 17α-Hydroxyiation*

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Abstract
A NADH-linked 17αhydroxylation of progesterone was examined using the washed microsomefraction prepared from human testes. The addition of NADP revealed no enhancement of 17α-hydroxylation, indicating no transhydrogenation from NADH to NADP in the microsome fraction. The results further substantiate the presence of NADH-linked activity of 17α-hydroxylase in addition to NADPH-linked activity. The Km of 17α-hydroxylase for NADH was calculated as 4.3×10-5 M at pH 7.4 and 37 C. The optimal pH of 17α-hydroxylase was 7.7 in the presence of NADH and 7.9 in the presence of NADPH. An additive increase in the amount of product 17α-hydroxyprogesterone was observed by adding NADH to the incubation medium containing an excess amount of NADPH. The data suggest that there are two distinct active sites for 17α-hydroxylation. Furthermore,the inhibition of NADH-linked 17α-hydroxylation by carbon monoxide indicates the involvement of cytochrome P450 in the electron transport system for the NADH-linked 17αhydroxylation.

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