Glucuronidation of testosterone by rat liver microsomes.

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Abstract
The properties of testosterone glucuronyltransferase of rat liver microsomes were studied. The conjugate which was formed from testosterone was identified as the 17.beta.-glucuronide by TLC, hydrolysis with .beta.-glucuronidase, and reverse isotope dilution analysis of the acetate-methyl ester derivative. The microsomal testosterone glucuronyltransferase of liver increased with age of the animals up to 15-16 wk. 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 Vmax value. Pretreatment of the animals with phenobarbital, 3-methylcholanthrene, diphenylhydantoin, phenylbutazone, or with DDT increased liver glucuronyltransferase activity by 130-230%. The microsomes obtained from 3-methylcholanthrene-treated rats showed the glucuronyltransferase activity with a 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.