Inhibition byl-phenylalanine of tryptophan transport by synaptosomal plasma membrane vesicles: Implications in the pathogenesis of phenylketonuria

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Abstract
Phenylalanine is accumulated in the genetically linked deficiency phenylketonuria. The effect ofl-phenylalanine on the transport of tryptophan was studied using membrane vesicles from rat-brain synaptosomes. Phenylalanine at similar concentrations to those found in phenylketonuric patients competitively inhibits tryptophan uptake, with aK i of the same order as theK m for tryptophan. This inhibition could be responsible for the depletion of serotonin found in phenylketonuria.