title: Interference of UDP-glucuronyltransferase and beta-glucuronidase activity in rat liver microsomes at pH 7.5 with p-nitrophenol and p-nitrophenylglucuronide as substrates.
abstract: Microsomal fraction contains the whole of hepatic UDP-glucuronyltransferase as well as part of beta-glucuronidase. The activities of the two enzymes were assayed under identical conditions using untreated male rat liver microsomes at pH 7.5. In a 30-min incubation with p-nitrophenol and UPD-glucuronic acid, a net glucuronide formation of 0.010 mumol.min-1.g.liver-1 was measured. In the presence of saccharolactone at concentrations selectively blocking beta-glucuronidase, the glucuronidation rate was 0.015 mumol.min-1.g.liver-1. Using the kinetic parameters of beta-glucuronidase (Km = 0.06 mmol/l p-nitrophenylglucuronide, Vm = 0.075 mumol pNP formed.h-1.g.liver-1) determined in the absence of UDP-glucuronic acid, to correct for the beta-glucuronidase's interference on the glucuronidation process, a glucuronide formation of 0.011 mumol.min-1.g.liver-1 was calculated.
mesh_terms: D000818:Animals; D005937:Glucaric Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005966:Glucuronidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007783:Lactones / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009596:Nitrophenols / Q000378:metabolism; D051381:Rats
chemical_list: D007783:Lactones; D009596:Nitrophenols; C009194:saccharolactone; D014453:Glucuronosyltransferase; D005966:Glucuronidase; D005937:Glucaric Acid