Induction of rat liver cytosol methyl red azo-reductase by 3-methylcholanthrene assayed by a sensitive fluorometric method.

Abstract A sensitive and rapid fluorometric assay has been developed to measure the reduction of methyl red by rat liver enzymes. Greater than 90% of the methyl red reductase activity is found in the cytosol rather than in microsomes. The cytosol reductase activity is induced 7 to 10-fold by pretreatment of rats with 3-methylcholanthrene while little or no increase in activity is observed after phenobarbital treatment. The cytosol reductase activity is not inhibited by oxygen. Thus, the properties of the cytosol azo-reductase are quite different from those of the microsomal azo-reductases.