Influence of Microsomal and Cytosolic Fractions from the Liver of 4 Animal Species and Man on the Mutagenicity of Carcinogenic Aminoazo Dyes and Nature of the Mutagenicity-Enhancing Factor in the Cytosol from Rat Liver

The mutagenicity of 3'-methyl-N, N-dimethyl-4-aminoazobenzene (3'-Me-DAB) and 3'-CH2OH-DAB, potent hepatocarcinogens, was examined. Microsomal and cytosolic fractions from rat, mouse, hamster, rabbit, and human livers were used for metabolic activation, with Salmonella typhimurium TA100 or TA98 as a tester strain. The mutagenicity of both aminoazo dyes mediated by liver microsomes from polychlorinated biphenyls (PCB)-induced rats was markedly enhanced by addition of the hepatic cytosol ; it was also enhanced by addition of the hepatic cytosol from uninduced rats and phenobarbital-or 3-methylcholanthrene (3-MC)-induced rats. Similar mutagenesis enhancement was produced by cytosols from PCB-induced mice, hamsters, or female rats. The cytosols from rabbit and human liver enhanced the mutagenicity of 3'-CH2OH-DAB but not that of 3'-Me-DAB. Heating of the cytosol from uninduced rat liver to 55°C for 15 min caused a loss of most of the enhancement activity ; at 40°C, it was stable. About 30% of the enhancement activity for both aminoazo dyes was lost upon dialysis for 24h at 4°C. Protein fractions with the aminoazo dye mutagenicity-enhancing activity were obtained from the dialyzed cytosol by gel filtration through Sephadex G-100 ; the protein fraction with the greatest activity, representing an approximately 3-fold increase in specific activity, was assigned a molecular weight of 43000-47500. This protein preparation enhanced microsome-mediated mutagenesis by 3'-hydroxymethyl-N-methyl-4-aminoazobenzene and o-aminoazotoluene but not that by 3-MC, benzo [a] pyrene, or dimethylnitrosamine.