RT Journal Article SR Electronic T1 Studies on tertiary amine UDP-glucuronosyltransferases from human and rabbit hepatic microsomes. JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 896 OP 901 VO 20 IS 6 A1 P B Styczynski A1 M D Green A1 B Coffman A1 T R Tephly YR 1992 UL http://dmd.aspetjournals.org/content/20/6/896.abstract AB The conversion of tertiary amines to quaternary ammonium glucuronides was investigated in human liver microsomes, and characteristics of the UDP-glucuronosyltransferase (UGT) catalyzing quaternary ammonium glucuronidation were evaluated. In addition, a rabbit liver microsomal UGT mediating this reaction was studied. The kinetics of quaternary ammonium glucuronidation of cyproheptadine, tripelennamine, amitriptyline, and doxepin in intact human liver microsomes was determined. Tripelennamine was found to have the lowest apparent KM and was used as a representative substrate for further studies. A polyclonal antibody preparation raised in sheep against rabbit liver p-nitrophenol UGT was found to inhibit tripelennamine glucuronidation in solubilized human liver microsomes, but had no effect on p-nitrophenol, 4-methylumbelliferone, 4-aminobiphenyl, estriol, morphine, or naloxone glucuronidation. This antibody also inhibited tripelennamine glucuronidation in solubilized rabbit liver microsomes, but had little or no effect on estrone, testosterone, estradiol, androsterone, and morphine glucuronidation. Chlorpromazine competitively inhibited tripelennamine glucuronidation. This inhibition was markedly enhanced by UV light irradiation. [3H] Chlorpromazine binding to solubilized human liver microsomes was also increased by UV light. The binding was antagonized by substrates for tertiary amine UGT but not by substrates for morphine UGT. These studies suggest that the tertiary amine UGT is photo-affinity-labeled by chlorpromazine. Furthermore, it would appear from immunoinhibition and [3H]chlorpromazine labeling experiments that tertiary ammonium glucuronidation is catalyzed by a unique and distinct UGT in rabbit and human liver microsomes.