Abstract
The properties of testosterone glucuronyltransferase of rat liver microsomes were studied. The conjugate which was formed from testosterone was identified as the 17β-glucuronide by thin-layer chromatography, hydrolysis with β-glucuronidase, and reverse isotope dilution analysis of the acetate-methyl ester derivative. The microsomal testosterone glucuronyltransferase of liver was shown to increase with age of the animals up to 15-16 weeks. Treatment of the isolated microsomes with Triton X-100 or with deoxycholate enhanced apparent glucuronyltransferase activity 5-and 2-fold at maximum, respectively. This increase of the enzyme activity was due to the elevation of the V max value. Pretreatment of the animals with phenobarbital, 3-methylcholanthrene, diphenylhydantoin, phenylbutazone, or with 1, 1, 1-trichloro-2, 2-bis (p-chlorophenyl) ethane (DDT) increased the liver glucuronyltransferase activity by 130-230%. The microsomes obtained from 3-methylcholanthrene-treated rats showed the glucuronyltransferase activity with smaller Km value for testosterone. The kinetic studies also demonstrated that p-nitrophenol inhibited glucuronidation of testosterone competitively, whereas both bilirubin and estradiol inhibited the reaction noncompetitively.
