title: The metabolism of L-m-tyrosine: the use of a putative precursor to investigate the increased production of m-hydroxymandelic acid in phenylketonuria.
abstract: 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.
mesh_terms: D015078:2-Hydroxyphenethylamine / Q000031:analogs & derivatives / Q000378:metabolism; D015102:3,4-Dihydroxyphenylacetic Acid / Q000652:urine; D000328:Adult; D005260:Female; D006801:Humans; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D008333:Mandelic Acids / Q000652:urine*; D009655:Octopamine / Q000031:analogs & derivatives*; D010648:Phenylacetates / Q000652:urine; D010661:Phenylketonurias / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D008333:Mandelic Acids; D010648:Phenylacetates; D015102:3,4-Dihydroxyphenylacetic Acid; D009655:Octopamine; C024037:3-hydroxymandelic acid; D014443:Tyrosine; D015078:2-Hydroxyphenethylamine; C005310:norfenefrine; C015566:3-tyrosine; C008069:3-hydroxybenzeneacetic acid