Kinetic constant determination of liver microsomal and purified UDP-glucuronosyltransferase after phenobarbital and 3-methylcholanthrene treatments in rats.
After induction by phenobarbital and 3-methylcholanthrene, UDP-glucuronosyltransferase involved mainly in the conjugation of planar substrates was purified. Compared to the microsomal enzyme, the purified protein exhibited less affinity towards the substrates, but the corresponding Vmaxs were increased. These results were attributed to a change in the lipid environment of the purified enzyme. The conjugation rate for 4-hydroxycoumarine was 15-45 times less than that measured for the 7-hydroxyisomer with the microsomal or the purified enzymes. Immunoprecipitation studies of the enzyme revealed that the two compounds were transformed by the same enzyme, or metabolized by two separate enzymes presenting the same antigenic site. The orientation of the hydroxyl group of planar aglycones in the active site is the determinant for the efficiency of catalysis.
Thomassin
J
J
Dragacci
S
S
Faye
B
B
Magdalou
J
J
Siest
G
G
D000818:Animals; D004790:Enzyme Induction / Q000187:drug effects; D014453:Glucuronosyltransferase / Q000096:biosynthesis*; D066298:In Vitro Techniques; D007700:Kinetics; D050356:Lipid Metabolism; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D008748:Methylcholanthrene; D014453:Glucuronosyltransferase; D010634:Phenobarbital