UDPGlucuronosyltransferase and Mixed Function Oxidase Activity in Microsomes Prepared by Differential Centrifugation and Calcium Aggregation

Abstract

Microsomes were prepared from the liver, kidney and lung of phenobarbital or 20-methylcholanthrene treated and control rats with the conventional ultracentrifugation and Ca aggregation methods. The 2 methods were compared as to the yield of microsomal protein, amount of cytochrome P-450/448 and activity of UDP glucuronosyltransferase, benzopyrene hydroxylase and p-nitroanisole O-demethylase. The absolute amount of cytochrome P-450/448 (nmol/g wet wt) and the enzymatic activities dependent on it (nmol produced/g wet wt) did not differ significantly in any tissue of either treated or control animals nor did that of UDP glucuronosyltransferase. The ultracentrifugation method resulted in a slightly smaller yield of hepatic microsomal protein and a correspondingly higher yield of cytochrome P-450/448 per mg protein as well as higher specific enzymatic activities of both the consecutive drug biotransformation reactions studied. The specific activity of UDP glucuronosyltransferase in digitonin treated microsomes was twice as high in the conventional microsomes as in the Ca aggregated microsomes; no differences was found in the trypsin treated microsomes. The specific activity of the hepatic benzypyrene hydroxylase of the benzypyrene treated animals in the Ca harvested microsomes was 55% of that in the ultracentrifugated microsomes.