Cloning and substrate specificity of a human phenol UDP-glucuronosyltransferase expressed in COS-7 cells

A rat kidney phenol UDP-glucuronosyltransferase cDNA was used to isolate a human liver phenol UDP-glucuronosyltransferase cDNA by screening of a human liver cDNA library in the expression vector lambda gt11. The 2.4-kilobase cDNA contained an open reading frame of 1593 base pairs coding for a protein of 531 residues. The human liver cDNA was subcloned into the vector pKCRH2. Transfection of this recombinant plasmid into COS-7 cells allowed the expression of a protein of approximately 55 kDa. The enzyme synthesized was a glycoprotein, as indicated by a reduction in molecular mass of approximately 3 kDa after biosynthesis in the presence of tunicamycin. The expressed enzyme rapidly catalyzed the glucuronidation of 1-naphthol, 4-methylumbelliferone, and 4-nitrophenol. The use of a related series of simple phenols provided an outline description of the substituent restrictions imposed upon the phenolic structures accepted as substrates. The glucuronidation of testosterone, androsterone, and estrone was not catalyzed by this cloned UDP-glucuronosyltransferase.