RT Journal Article SR Electronic T1 Purification and properties of two rat liver phenobarbital-inducible UDP-glucuronosyltransferases that catalyze the glucuronidation of opioids. JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 329 OP 333 VO 24 IS 3 A1 B L Coffman A1 G R Rios A1 T R Tephly YR 1996 UL http://dmd.aspetjournals.org/content/24/3/329.abstract AB Glucuronidation of xenobiotics and endobiotics is catalyzed by a group of intrinsic membrane proteins of the endoplasmic reticulum of cells: the UDP-glucuronosyltransferases. Two isoforms with glucuronidation activity toward opioids have been purified and characterized from liver microsomes obtained from phenobarbital-treated Wistar rats. The proteins have been identified as the gene products of UGT2B1 and UGT1.1r. The purified proteins exhibited the same apparent KM values for morphine glucuronidation (2-3 mM). However, the purified UGT1.1r enzyme exhibited glucuronidation activity toward buprenorphine and bilirubin with high efficiency, but the UGT2B1 protein did not react with these compounds. Both purified enzymes glucuronidated chloramphenicol, 4-hydroxybiphenyl, chrysin, and ibuprofen. Flunitrazepam photoaffinity labeling was demonstrated for both enzymes, and naloxone, the opioid antagonist, antagonized the photoaffinity labeling reactions.