Inhibition of rat alpha-reductases by finasteride: evidence for isozyme differences in the mechanism of inhibition.
The mechanism of inhibition of the rat types 1 and 2 5alpha-reductase by finasteride was investigated using recombinantly expressed enzymes. These studies revealed that finasteride is a potent, reversible inhibitor of the rat type 1 5alpha-reductase with Ki=10.2+/-1.3 nM. Finasteride is a potent inhibitor of the rat type 2; however, in this case the compound binds to the type 2 isozyme-NADPH complex to form a ternary complex with Ki=1.19+/-0.10 nM, which then rearranges to a high affinity complex (E:I) with a pseudo first order rate constant of 1.62+/-0.22 x 10(-3)/s. The second order rate constant is k3/Ki=1.37+/-0.31 x 10(6) M/s. Heat denaturation of the (type 2 enzyme:inhibitor) complex releases dihydrofinasteride and presumably the NADP+-adduct previously identified with the human 5alpha-reductases. The effects of finasteride were also studied in intact COS cells transiently expressing the rat types 1 and 2 5alpha-reductase. Results with whole cell assays confirm differences in mechanism of inhibition of rat types 1 and 2 5alpha-reductase by finasteride.
Azzolina
B
B
Department of Enzymology, Merck Research Laboratories, Rahway, NJ 07065, U.S.A.
Ellsworth
K
K
Andersson
S
S
Geissler
W
W
Bull
H G
HG
Harris
G S
GS
D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000235:genetics; D058891:5-alpha Reductase Inhibitors; D000818:Animals; D019556:COS Cells; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018120:Finasteride / Q000494:pharmacology*; D006358:Hot Temperature; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D007700:Kinetics; D009249:NADP / Q000378:metabolism; D011489:Protein Denaturation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins
D058891:5-alpha Reductase Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D011993:Recombinant Fusion Proteins; D009249:NADP; D018120:Finasteride; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase