Effect of fasting on substrate specificity of rat liver UDP-glucuronosyltransferase.
The effect of a 3-day period of complete starvation on the hepatic UDPglucuronosyltransferase activity was studied in the rat. The substrate specificity of the enzyme was assayed with bilirubin as a carboxylic acceptor, and phenolphthalein and p-nitrophenol as phenolic acceptors. Starvation increased the bilirubin UDPglucuronosyltransferase specific activity by 33%, whereas no increase in specific activities appeared when the phenolic substrates were used. However, on a total liver weight basis, all three activities were significantly lower than those of the controls. Kinetic studies of activated microsomal bilirubin UDPglucuronosyltransferase showed that apparent Km values were similar; fasting acted only by increasing V. The results suggest that the changes in bilirubin glucoronosyltransferase activity provoked by starvation may reflect actual enzyme induction; they favour the multiplicity of the UDPglucuronosyltransferase system.
D000818:Animals; D001663:Bilirubin / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006602:Hexosyltransferases / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D009596:Nitrophenols / Q000378:metabolism; D009929:Organ Size; D010635:Phenolphthaleins / Q000378:metabolism; D051381:Rats; D013217:Starvation
D009596:Nitrophenols; D010635:Phenolphthaleins; D006602:Hexosyltransferases; D014453:Glucuronosyltransferase; D001663:Bilirubin