Human TRP-1 has tyrosine hydroxylase but no dopa oxidase activity

Pigment Cell Res. 1994 Jun;7(3):131-40. doi: 10.1111/j.1600-0749.1994.tb00040.x.


Human TRP-1 has been immunopurified from normal human melanocytes cultured from black neonatal subjects and used to investigate the catalytic function of TRP-1 for the two substrates, L-tyrosine and L-DOPA. Immunopurified TRP-1 did not demonstrate DOPA staining on SDS/PAGE nor DOPA oxidase (DO) activity with either routine or modified assays. The purified TRP-1 also demonstrated no tyrosine hydroxylase (TH) activity using the routine Pomerantz assay. However, there was apparent TH activity exhibited by immunopurified TRP-1 under conditions with low tyrosine concentration (< or = 0.8 microCi/ml of 3H-tyrosine), prolonged incubation time (i.e., overnight) and in the absence of the cofactor L-DOPA. Using these latter specific conditions, TH activity was also detected in cell lysates from a tyrosinase-negative albino melanocyte line which exhibited no TH activity with the routine Pomerantz assay. In addition, TH activity under low substrate assay conditions was not exhibited in a melanocyte line derived from a TRP-1 deficient, Brown albino individual. However, the absence of TH in this Brown albino cell line could be compensated for by the addition of L-DOPA to the assay. These results suggested that TRP-1 has some tyrosine hydroxylase but no DOPA oxidase activity. We propose that one function of TRP-1 is to modulate tyrosinase activity by making DOPA available as a cofactor to perpetuate the initial steps in melanogenesis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cells, Cultured
  • Chromatography, Affinity
  • Dihydroxyphenylalanine
  • Electrophoresis, Polyacrylamide Gel
  • Humans
  • Infant, Newborn
  • Male
  • Melanins / biosynthesis
  • Melanocytes / cytology
  • Melanocytes / enzymology
  • Membrane Glycoproteins*
  • Monophenol Monooxygenase / metabolism*
  • Oxidoreductases*
  • Proteins / isolation & purification
  • Proteins / metabolism*
  • Substrate Specificity
  • Tyrosine
  • Tyrosine 3-Monooxygenase / metabolism*


  • Melanins
  • Membrane Glycoproteins
  • Proteins
  • Tyrosine
  • Dihydroxyphenylalanine
  • Oxidoreductases
  • Tyrosine 3-Monooxygenase
  • TYRP1 protein, human
  • tyrosinase-related protein-1
  • Monophenol Monooxygenase