Biochemical properties of some microsomal xenobiotic-metabolizing enzymes in rabbit small intestine

Comparison of xenobiotic-metabolizing enzymes in rabbit small intestinal and hepatic microsomal fractions showed mainly quantitative differences; most of the activities were two to seven times higher in liver than in intestine. However, UDP-glucuronyltransferase activity was higher in intestine than in liver. The apparent absence of benzene hydroxylase in small intestine was the only qualitative difference noticed. Aniline hydroxylase, aminopyrine N-demethylase, and aryl hydrocarbon dydroxylase were characterized in intestinal microsomes and compared to those of liver. Distribution of these enzymes along the entire length of small intestine showed that maximum activities of the enzymes were present in the proximal 60 cm of the intestine. All the enzymes in both tissues required NADPH and O2 for maximum activity and were inhibited by cytochrome c, SKF 525-A, and CO. The in vitro addition of drug substrates to microsomal fractions of both tissues produced typical type I and type II binding spectra. Comparison of the relationships between activities and pH, duration of incubation, and substrate and protein concentration suggested that the rabbit intestinal and hepatic xenobiotic-metabolizing enzymes studied have similar characteristics.