PT - JOURNAL ARTICLE AU - Coffman, B L AU - Rios, G R AU - Tephly, T R TI - Purification and properties of two rat liver phenobarbital-inducible UDP-glucuronosyltransferases that catalyze the glucuronidation of opioids. DP - 1996 Mar 01 TA - Drug Metabolism and Disposition PG - 329--333 VI - 24 IP - 3 4099 - http://dmd.aspetjournals.org/content/24/3/329.short 4100 - http://dmd.aspetjournals.org/content/24/3/329.full SO - Drug Metab Dispos1996 Mar 01; 24 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.