Kinetic studies of hepatocyte UDP-glucuronosyltransferase: evidence of an allosteric enzyme.
The kinetic analysis of the enzyme UDP-glucuronosyltransferase (UDPGT) responsible for the conjugation of bilirubin, suggest that it is a multisubunit enzyme in which there is cooperative binding of substrate to the subunits. The binding of bilirubin to UDP-glucuronosyltransferase shows positive cooperativity with an apparent dissociation constant of 7.824 x 10(-4) +/- 6.405 x 10(-4) mM. The apparent Hill coefficient for bilirubin to UDPGT is 2.9. The binding of UDP-glucuronic acid exhibits kinetics with mixed cooperativity. Analysis with the Hill equation give an apparent dissociation constant of 6.873 +/- 3.816 mM and a Hill coefficient of 4.028 +/- 1.045. These values of the Hill coefficient are consistent with an enzyme being an oligomer with 6 subunits, since the actual number of subunits must be greater than the apparent Hill coefficient.
Bruni
S
S
Artificial Cells & Organs Research Centre, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
Chang
T M
TM
D000494:Allosteric Regulation; D000818:Animals; D001663:Bilirubin / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000737:chemistry / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D011487:Protein Conformation; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism
D014535:Uridine Diphosphate Glucuronic Acid; D014453:Glucuronosyltransferase; D001663:Bilirubin