Abstract

The Michaelis constants (K_m values) for the oxidative metabolism of progesterone, testosterone, and estradiol-17β by liver microsomes from adult male rats were determined. These values ranged from 1.6 x 10^-5M to 4.9 x 10^-5M. Previous studies have suggested that oxidative drug-metabolizing enzymes have steroids as normal body substrates. This concept is consistent with the results presented here indicating that the K_m values for the oxidative metabolism of steroid hormones are about 10 times lower than the K_m values for the metabolism of several drugs.