Enhancement of hepatic microsome-mediated bacterial mutagenesis by the rat liver soluble protein fraction.

Bacterial mutagenesis from aflatoxin B1, 2-aminofluorene and benzo[a]-pyrene, mediated by washed rat liver microsomes using the assay system of Ames, is elevated 2--4-fold by the liver soluble protein fraction. Enhancement results from an apparent stimulation of one (or possible more) biochemical steps leading to mutagenesis in this system. Enhancement is observed over a wide range of NADPH concentrations and is present in dialyzed preparations of liver soluble proteins. Enhancement activity is stable when the soluble protein fraction is stored for 18 h at pH 5-9 (4 degrees C); when stored for 18 h at 25 degrees C or 37 degrees C (pH 7.8), and when heated for 10 min at 56 degrees C. The activity is labile when heated for 10 min at 100 degrees C.