Some properties of progesterone 5 alpha-reductase solubilized from rat liver microsomes.

The experiments described in this paper were undertaken to examine the requirements of NADPH-cytochrome c reductase and phosphatidylcholine for hepatic steroid 5 alpha-reduction, previously proposed by Golf and Graef (Golf, S. W. and Graef, V. (1978) J. Steroid Biochem. 9, 369-371). To determine how NADPH-cytochrome c reductase participates in hepatic 5 alpha-reductase activity, antibodies against the purified NADPH-cytochrome c reductase were added to 5 alpha-reductase preparation solubilized from rat liver microsomes. Whereas both NADPH-cytochrome c reductase and progesterone 16 alpha-hydroxylase in the preparation were inhibited by the antiserum, the inhibitory effect on 5 alpha-reductase activity was not observed. In addition, chromatography of the polyethylene glycol fraction active in 5 alpha-reduction on DEAE-cellulose resulted in the complete separation of 5 alpha-reductase activity from NADPH-cytochrome c reductase activity. Unlike NADPH-cytochrome c reductase, phosphatidylcholine increased the activity of the partially purified 5 alpha-reductase about 2.5 fold. Phosphatidylserine also enhanced the activity to an extent identical for phosphatidylcholine. Phosphatidic acid and lysophosphatidylcholine were stimulatory to lesser extents.