Purification and properties of a rat liver phenobarbital-inducible 4-hydroxybiphenyl UDP-glucuronosyltransferase

A phenobarbital-inducible rat hepatic microsomal UDP-glucuronosyltransferase (UDPGT) that catalyzes the glucuronidation of 4-hydroxybiphenyl (4-HBP) has been purified to homogeneity. This UDPGT has an apparent subunit molecular weight of 52,500, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The 4-HBP UDPGT was shown to catalyze the glucuronidation of 4-HBP, 4-methylumbelliferone, and p-nitrophenol but did not react with testosterone, androsterone, morphine, chloramphenicol, 4-hydroxycoumarin, or 7-methoxycoumarin. The apparent Km of 4-HBP UDPGT for 4-HBP was determined to be 0.26 mM and for UDPGA was 1.0 mM. Upon treatment with endoglycosidase H, the 4-HBP UDPGT underwent about a 2000-dalton decrease in subunit molecular weight, suggesting that this protein is N-glycosylated. Additionally, this protein demonstrated immunoreactivity with antibodies raised in rabbit against rat 17 beta-hydroxysteroid and 3 alpha-hydroxysteroid UDPGTs. This work describes the purification and characterization of a 4-HBP UDPGT from rat liver microsomes and, furthermore, provides evidence that suggests that this UDPGT is different from another UDPGT previously shown to react with 4-HBP and chloramphenicol.