GLUCURONIDATION OF RETINOIDS BY RAT RECOMBINANT UDP - GLUCURONOSYLTRANSFERASE-1.1 (BILIRUBIN UGT)

Rat liver recombinant BR(1)UGT1.1 was found to have significant activi ty toward retinoid substrates. UGT1.1 glucuronidation activity was 91 +/- 18 pmol/mg x min for atRA and 113 +/- 19 pmol/mg x min for 5,6-epo xy-atRA. The apparent K-M and V-max of atRA acid glucuronidation by UG T1.1 were 59.1 +/- 5.4 mu M and 158 +/- 43 pmol/mg x min, respectively . SDS-PAGE and Western blot analysis of UGT1.1-transfected HK293 membr ane proteins photolabeled with [11,12-H-3]atRA revealed a protein of s imilar to 56 kDa that was labeled by [H-3]atRA, detected by anti-pNP U GT antibody and not present in membranes from nontransfected HK293 cel ls. Liver microsomes from Gunn rats, which lack UGT1.1, had significan t activity toward atRA(111 +/- 28 pmol/mg x min).