The effect of phenobarbital on the submicrosomal distribution of uridine diphosphate glucuronyltransferase from rat liver.
1. The detergent Triton X-100 activates UDP glucuronyltransferase from rat liver in vitro six- to seven-fold with p-nitrophenol as substrate. The enzyme activity when measured in the presence of Triton X-100 is increased significantly by pretreatment of male rats with phenobarbital for 4 days (90mg/kg each day intraperitoneally). If no Triton X-100 is applied in vitro such an increase could not be shown. In all further experiments the enzyme activity was measured after activation by Triton X-100. 2. The K(m) of the enzyme for the substrate p-nitrophenol does not change on phenobarbital pretreatment. 3. When the microsomal fraction from the liver of untreated rats is subfractionated on a sucrose density gradient, 47% of the enzyme activity is recovered in the rough-surfaced microsomal fraction, which also has a higher specific activity than the smooth-surfaced fraction. 4. Of the increase in activity after the phenobarbital pretreatment 50% occurs in the smooth-surfaced fraction, 19% in the rough-surfaced fraction and 31% in the fraction located between the smooth- and rough-surfaced microsomal fractions on the sucrose density gradient. 5. The latency of the enzyme in vitro, as shown by the effect of the detergent Triton X-100, is discussed in relation to the proposed heterogeneity of UDP glucuronyltransferase.
D000818:Animals; D002499:Centrifugation, Density Gradient; D003902:Detergents; D004789:Enzyme Activation; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009596:Nitrophenols / Q000378:metabolism; D010634:Phenobarbital / Q000494:pharmacology*; D051381:Rats; D014166:Transferases / Q000032:analysis*; D014500:Uracil Nucleotides / Q000378:metabolism
D003902:Detergents; D009596:Nitrophenols; D014500:Uracil Nucleotides; D014166:Transferases; D010634:Phenobarbital