Presynaptic tyrosine availability in the phenylketonuric brain: a hypothetical evaluation.

From measured effects of amino acids on synaptosomal tyrosine uptake and from published data on human CNS levels of amino acids hypothetical calculations were made to compare CNS tyrosine availability for catecholamine synthesis in the hyperphenylalaninemic and non-hyperphenylalaninemic condition. These calculations indicate an approximately two-fold reduction in the availability of tyrosine in phenylketonuria that is due solely to a reduction in CNS tyrosine alone.