A Possible Mechanism for Disturbance in Tyrosine Metabolism in Phenylpyruvic Oligophrenia

In vitro, L-phenylalanine partially inhibits the action of tyrosinase on tyrosine. The amount of inhibition is directly related to the concentration of L-phenylalanine. 2. In the same concentration, D-phenylalanine produces no significant effect on the tyrosine-tyrosinase system. Parallel experiments with DL-alanine also indicate a specific effect by L-phenylalanine. 3. It is suggested that, because of the similarity in structure, L-phenylalanine competes with tyrosine for the enzyme tyrosinase. 4. The significance of these findings in phenylpyruvic oligophrenia is discussed.