title: Binding of a 4-methyl-4-aza-steroid to 5 alpha-reductase of rat liver and prostate microsomes.
abstract: A tritium labeled 5 alpha-reductase inhibitor, [1,2-3H] 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one ([3H]4-MA), binds reversibly to a high affinity site (Kd, 6.5 nM) in liver microsomes from male rats. The binding requires a nicotinamide nucleotide coenzyme; NADH is at least 100 times less potent than NADPH, and NADP+, NAD+, flavin adenine dinucleotide, coenzyme A, and ADP are inactive. The relative potencies of 13 steroids as inhibitors of the binding of [3H]4-MA to liver microsomes correlate with their relative potencies as inhibitors of the conversion of [14C]testosterone to [14C]5 alpha-dihydrotestosterone by liver microsomes. Comparison of liver microsomes from mature female rats and microsomes from mature male rat liver, ventral prostate, spleen, kidney, and skeletal muscle shows that their NADPH-dependent [3H]4-MA binding capacities correlate with their levels of 5 alpha-reductase activity. These results suggest that [3H]4-MA binds specifically to 5 alpha-reductase in a NADPH-dependent manner. 5 alpha-Reductase was solubilized from liver microsomes with a detergent, Lubrol-WX, and the solubilized enzyme also binds [3H]4-MA. The relative potencies of 13 steroids as inhibitors of rat ventral prostate and liver 5 alpha-reductase are the same, strongly suggesting that the 5 alpha-reductases in the two tissues are the same.
mesh_terms: D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism*; D000818:Animals; D001378:Azasteroids / Q000378:metabolism*; D013196:Dihydrotestosterone / Q000031:analogs & derivatives* / Q000378:metabolism; D008297:Male; D008861:Microsomes / Q000201:enzymology; D008862:Microsomes, Liver / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism*; D011467:Prostate / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013260:Steroids, Heterocyclic / Q000378:metabolism*
chemical_list: D001378:Azasteroids; D013260:Steroids, Heterocyclic; D013196:Dihydrotestosterone; D009243:NAD; D009249:NADP; C031563:17-N,N-diethylcarbamoyl-4-methyl-4-azaandrostane-3-one; D010088:Oxidoreductases; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase