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Competitive Inhibition of Mammalian Tyrosinase by Phenylalanine and its Relationship to Hair Pigmentation in Phenylketonuria


IN Jervis's introductory study, and in subsequent case reports of phenylketonuria (phenylpyruvic oligophrenia), a blonde hair colour and a fair skin have been noted in the large majority of the patients1–4. The most striking example described by Jervis was “an idiot baby with blonde hair and blue eyes who belonged to a family of Sicilian extraction, all the members of which, for at least three generations, were of a very dark Mediterranean race”1. Three possible hypotheses may be advanced to explain the reduction of melanin formation: absence of the melanin-forming enzyme, tyrosinase; absence or decrease of the melanin precursor, tyrosine; and finally, inhibition of the tyrosine–tyrosinase reaction by phenylalanine or related abnormal aromatic metabolites which accumulate in the blood of patients with phenylketonuria.

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