3-tyrosine and norfenefrine

Several urinary meta-substituted phenols appear to be of endogenous origin. However, the production of these compounds is reduced in phenylketonuria with the exception of m-hydroxymandelic acid whose excretion is approximately doubled. This phenomenon has been investigated in two patients with phenylketonuria using the putative precursor L-m-tyrosine labelled with deuterium. Metabolism of this compound in these patients was comparable to that in healthy adults although much less was converted to m-hydroxymandelic acid and the excretion pattern of this metabolite was different. This apparent anomaly is attributed to smaller metabolic compartments in phenylketonuria and a lower threshold for the metabolism of m-tyramine via beta-hydroxylation. Incorporation into the natural pathway was shown by depletion of endogenous m-hydroxymandelic acid. The results are further support for the ideas that the amine precursors of m-hydroxymandelic acid, m-tyramine and m-octopamine, have a functional role and may be important in the pathogenesis of phenylketonuria.

Topics: 2-Hydroxyphenethylamine; 3,4-Dihydroxyphenylacetic Acid; Adult; Female; Humans; Hydroxylation; Kinetics; Male; Mandelic Acids; Octopamine; Phenylacetates; Phenylketonurias; Tyrosine