A kinetic analysis of the 5 alpha-reductases from human prostate and liver.
A kinetic analysis of the 5 alpha-reductases from human liver and prostate is presented. Human prostatic 5 alpha-reductase follows an ordered sequential mechanism in which NADPH binds first followed by testosterone. The order of release of products is DHT followed by NADP+. The apparent Km of prostatic 5 alpha-reductase for testosterone is 0.0339 +/- 0.006 microM, while the apparent Km for NADPH is 2.52 +/- 0.65 microM. Human liver 5 alpha-reductase also follows a sequential mechanism. The apparent Km of the liver enzyme is 0.110 +/- 0.08 microM; the apparent Km for NADPH is 6.2 +/- 0.6 microM. The fact that both the liver and prostatic 5 alpha-reductases have a sequential kinetic mechanism rules out the possibility that the reduction of testosterone to dihydrotestosterone involves an electron transport system as previously proposed.
Houston
B
B
University Department of Surgery (WGH), Western General Hospital, Edinburgh, UK.
Chisholm
G D
GD
Habib
F K
FK
D042944:Cholestenone 5 alpha-Reductase; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D010088:Oxidoreductases / Q000032:analysis*; D011467:Prostate / Q000201:enzymology*
D010088:Oxidoreductases; D042944:Cholestenone 5 alpha-Reductase