The effects of reserpine, alpha-methyltyrosine, and L-3,4-dihydroxyphenylalanine on brain tyrosine transaminase.

The effects of a variety of pharmacological and physiological manipulations on the activity of hepatic tyrosine transminase have been extensively investigated. Brain tyrosine transaminase, however, has received only limited attention. Since tyrosine transaminase may be important in the regulation of catecholamine biosynthesis in the brain, the effects of agents affecting catecholamine storage and synthesis on brain tyrosine transamination were investigated. Transamination in the 12,000 x g fraction was measured by a radioactive procedure. alpha-Methyltyrosine and reserpine, agents which deplete brain catecholamines, decreased tyrosine transaminase activity. Administration of the catecholamine precursor, L-3,4-dihydroxyphenylalanine to the reserpine-and alpha-methyltyrosine-treated rats elevated the tyrosine transaminase activity to normal. The possible implications of these findings in the regulation of the biosynthesis of the catecholamines are discussed.