Inhibition by L-phenylalanine of tyrosine transport by synaptosomal plasma membrane vesicles: implications in the pathogenesis of phenylketonuria.

The effect of L-phenylalanine on the transport of tyrosine was studied using membrane vesicles from rat brain synaptosomes. Phenylalanine, which is accumulated in phenylketonuria, competitively inhibits tyrosine uptake at concentrations similar to those found in phenylketonuric patients, with a Ki of the same order of the Km for tyrosine. This inhibition could be responsible for the depletion of catecholamines observed in phenylketonuria.