Properties and subcellular distribution of delta4-steroid (progesterone) 5alpha-reductase in rat anterior pituitary.
The properties and subcellular distribution of anterior pituitary delta4-steroid (progesterone) 5alpha-reductase, which stimulates the conversion of progesterone to 5alpha-pregnane-3,20-dione, have been investigated utilizing 3H-substrate and a reverse isotopic dilution assay system. The enzymic activity was stimulated by NADPH but not NADH and exhibited a Km of 2.7+/-0.9 times 10(-7) M for progesterone. The substrate specificity of the enzyme for other delta4-3-ketosteroids and the effect of estradiol-17beta were also studied. 20alpha-hydroxy-4-pregnen-3-one was more reactive than progesterone, while testosterone was less reactive. Estradiol-17beta in vitro had an inhibitory effect on the 5alpha-reduction of progesterone. Studies on the subcellular distribution of the 5alpha-reductase activity indicate that the bulk of the activity was widely distributed amongst particulates sedimenting at 1,000, 15,000 and 100,000xg; with the 15,000xg pellet containing the most enzymic activity. The 100,000xg supernatant possessed only a small fraction of the total activity. After further fractionation of the 1,000xg pellet, the activity was distributed equally between the purified nuclear and cell debris-membranes fractions.
D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002467:Cell Nucleus / Q000201:enzymology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D010902:Pituitary Gland / Q000201:enzymology*; D010903:Pituitary Gland, Anterior / Q000201:enzymology* / Q000648:ultrastructure; D011374:Progesterone / Q000378:metabolism; D011375:Progesterone Reductase / Q000378:metabolism*; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology
D011374:Progesterone; D004958:Estradiol; D006913:Hydroxysteroid Dehydrogenases; D011375:Progesterone Reductase