Biochemical characterization of prostaglandin 19-hydroxylase of seminal vesicles.

Abstract

The microsomal fraction of homogenates of seminal vesicles of men and monkeys, Macaca fascicularis, were analyzed for prostaglandin (PG) 19-hydroxylase activity. The microsomes of the monkey seminal vesicles, supplemented with 1 mM NADPH, metabolized 0.2 mM PGE1 to 19-hydroxy-PGE1 at a mean rate of 0.26 nmol/min/mg of protein (with an apparent Km and an apparent Vmax of 40 microM and 0.30 nmol/min/mg of protein, respectively). The enzyme catalyzed the incorporation of atmospheric oxygen into the substrate. Substituting NADH for NADPH reduced the prostaglandin E1 19-hydroxylase activity to 40%. Carbon monoxide and proadifen (SKF 525A) inhibited the enzyme. Prostaglandin E2 (0.2 mM) was metabolized to 19-hydroxyprostaglandin E2 (0.2 nmol/min/mg of protein), but PGE1 was preferred as a substrate. Prostaglandin B1 was metabolized to 18-hydroxy-, 19-hydroxy-, and 20-hydroxyprostaglandin B1 at a combined rate of approximately 25% of prostaglandin E1. 19-Hydroxyprostaglandin B1 was the main product. The microsomes of human seminal vesicles metabolized 0.2 mM PGE2 to 19-hydroxy-PGE2 in the presence of 1 mM NADPH, while carbon monoxide inhibited this reaction. These results suggest that prostaglandin 19-hydroxylase of seminal vesicles might be a cytochrome P-450. The biosynthesis of 19-hydroxyprostaglandin E1 and 19-hydroxyprostaglandin E2 was also studied in vivo in man by analysis of the product/substrate ratios (i.e. 19-hydroxyprostaglandin E1/prostaglandin E1 and 19-hydroxyprostaglandin E2/prostaglandin E2) in a series of consecutive ejaculates, which were obtained during short intervals. There was a 10-fold interindividual difference in these ratios. Although the product/substrate ratios decreased, the 19-hydroxylation of E prostaglandins appeared to be efficient in vivo, which was in contrast to the rather slow biosynthesis in vitro.