Effect of amino acids and inducers on the activity of the microsomal mono-oxygenase system in rat liver cell culture.

In rat liver cell culture both benzanthracene and phenobarbitone induce the activity of benzypyrene hydrxylase while only phenobarbitone increases NADPH cytochrome c reductase activity. Benzpyrene hydroxylase but not NADPH cytochrome c reductase activity is dependent on the amino acid concentration of the culture medium in a similar manner to the regulation of the hepatic hydroxylase activity by dietary protein intake in the whole animal. Of all the amino acids present in the culture medium, only tryptophan induced benzpyrene hydroxylase when added singly to the medium. However, tryptophan also induced the activity of the reductase suggesting that its inducing effect is unrelated to raising the concentration of all the amino acids of the culture medium. It is proposed that tryptophan may only be an inducer because the cells have low levels of tryptophan pyrrolase activity.