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Updated: Aug 18, 2026

Fast and Specific Assessment of the Halogenating Peroxidase Activity in Leukocyte-enriched Blood Samples
Published on: July 28, 2016
A study of the supposed hydroxylation of tyrosine catalysed by peroxidase
Abstract:
The claim that peroxidase (rather than tyrosinase) is the enzyme responsible for the conversion of tyrosine into dopa (3,4-dihydroxyphenylalanine) in melanogenesis was investigated. The spectral changes that occurred during the action of horseradish peroxidase in the presence of H2O2 on dopa, tyrosine and mixtures of dopa with tyrosine or other phenolic compounds were studied. The effect of ascorbic acid or dihydroxyfumaric acid on some of these changes was also investigated. No evidence was found that tyrosine was hydroxylated by peroxidase in the presence of H2O2 and dopa as cofactor, although tyrosine or other phenolic compounds increased the rate of oxidation of dopa to dopachrome (indoline-5,6-quinone-2-carboxylic acid). Peroxidase was, however, effective in oxidizing tyrosine to dopa in the presence of dihydroxyfumaric acid and oxygen.
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