Formation of m-tyrosine and o-tyrosine from L-phenylalanine in various tissues of rats.

Abstract

The hydroxylation of L-phenylalanine was investigated in subcellular fractions of various organs of rat under aerobic conditions. L-Phenylalanine was metabolized to p-, m-, and o-tyrosine in the 2000.times. g homogenates of liver, kidney, brain and adrenal of male rats. The three metabolites in the incubation mixture were deterined by high-performance liquid chromatography. This hydroxylation reaction occurred only in the postmicrosomal fraction of the organs mentioned above but not in the microsomal fractions, and required a pteridine as a cofactor. The hydroxylation of phenylalanine was inhibited by the addition of p-chlorophenylalanine and .alpha.-methyltyrosine, which are specific inhibitors of phenylalanine hydroxylase and tyrosine hydroxylase, respectively. On the other hand, superoxide dismutase and potassium iodide, which are known scavengers of the superoxide radical and hydroxyl radical, had no significant effect on the hydroxylation. These results indicate that the hydroxylation of phenylalanine to m- and o-tyrosines is caused mainly by phenylalanine hydroxylase and tyrosine hydroxylase.