Studies on the Binding and Distribution of Radioactively Labelled 3′-Methylcholanthrene in Subcellular Fractions of Rat Liver

The subcellular distribution of either [(14)C] or [(3)H]3′-methylcholanthrene was studied in rat liver following a single intraperitoneal injection of the labelled hydrocarbon 10 hours previously. Adsorbed or non-covalently bound methylcholanthrene and its metabolic derivatives occurred in all cell fractions studied with the exception of purified cell walls. The highest specific activities (d.p.m./mg. protein) were found in washed mitochondria, microsomes and ribosome-free microsomal membranes. Covalent binding of methylcholanthrene and its metabolic derivatives to different cell fractions of rat liver occurs to a small extent and is considered not to be significant. The highest degree of binding occurs in washed mitochondria, microsomes, ribosome-free microsomal membranes and their constituent core proteins. Cell sap which contains non-covalently bound 3′-methylcholanthrene was fractionated into pH 5 enzyme and pH 5 supernatant fractions. The pH 5 enzyme fraction which possesses a high specific activity (d.p.m./mg. protein) was further fractionated with ammonium sulphate into three fractions. The 0-30% ammonium sulphate fraction had the highest specific activity.