Analysis of the interaction uridin 5'-diphosphoglucuronic acid with intestinal bilirubin UDP-glucuronyltransferase.
1. Bilirubin UDP-glucuronyltransferase Michaelis-Menten kinetic parameters for UDP-glucuronic acid were studied using native and digitonin activated microsomes obtained from rat intestinal mucosa. 2. The intestinal enzyme showed a lower apparent Vmax compared with the hepatic enzyme in both native and activated microsomes; digitonin pretreatment enhanced Vmax 4 times in the former enzyme and 2 times in the latter. 3. The affinity of UDP-glucuronic acid for the intestinal enzyme was about 2 times lower than that for the hepatic enzyme and it was not substantially modified by detergent neither in the intestine nor in the liver. 4. The lipid analysis of intestinal and hepatic microsomes showed that the former present a higher content of cholesterol and a lower phosphatidylcholine/sphingomyelin ratio than the latter, accordingly the estimation of membrane fluidity using the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene indicated that intestinal microsomes are more "rigid" than the hepatic ones. 5. These characteristics would provoke a restrictive milieu surrounding the enzyme that modifies its kinetic properties thus limiting its participation in the metabolism of bilirubin.
Pozzi
E J
EJ
Instituto de Fisiología Experimental, Universidad Nacional de Rosario, Argentina.
Garay
E A
EA
Mottino
A D
AD
D000818:Animals; D005454:Fluorescence Polarization; D014453:Glucuronosyltransferase / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000201:enzymology*; D007425:Intracellular Membranes / Q000737:chemistry; D007700:Kinetics; D008055:Lipids / Q000032:analysis; D008099:Liver / Q000201:enzymology; D008297:Male; D008560:Membrane Fluidity; D008861:Microsomes / Q000737:chemistry / Q000201:enzymology; D008862:Microsomes, Liver / Q000737:chemistry / Q000201:enzymology; D051381:Rats; D017208:Rats, Wistar; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism*
D008055:Lipids; D014535:Uridine Diphosphate Glucuronic Acid; D014453:Glucuronosyltransferase