Comparative biochemistry and physiology. Part C, Pharmacology, toxicology & endocrinology 1995-11-01

Inhibition of UDP-glucuronyltransferase activity in rat liver microsomes by pyrimidine derivatives.

Z Naydenova, K Grancharov, M Shopova, E Golovinsky

Index: Comp. Biochem. Physiol. C, Pharmacol. Toxicol. Endocrinol. 112(3) , 321-5, (1995)

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Abstract

Thirty-one differently substituted pyrimidine bases were tested for their inhibitory effect on the glucuronidation of 4-nitrophenol and phenolphthalein by rat liver microsomes. 5-Nitrouracil (compound 1) and its isomer 4,6-dihydroxy-5-nitropyrimidine (compound 2) were the most potent and selective inhibitors of 4-nitrophenol glucuronidation, without any effect on the phenolphthalein conjugating activity of UDP-glucuronyltransferase (UGT). Kinetic studies with compound 1 revealed a mixed type of inhibition toward the acceptor substrate 4-nitrophenol and an atypical competitive type of inhibition toward UDP-glucuronic acid, with apparent Ki values of 0.11 and 0.2 mM, respectively. Two benzylamino-substituted pyrimidines (compounds 10 and 12) and an orotic acid derivative (compound 25) inhibited both 4-nitrophenol and phenolphthalein UGT activities.