Human TRP-1 has tyrosine hydroxylase but no dopa oxidase activity.
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.
Zhao
H
H
Department of Dermatology, University of Cincinnati College of Medicine, Ohio 45267-0592.
Zhao
Y
Y
Nordlund
J J
JJ
Boissy
R E
RE
D002478:Cells, Cultured; D002846:Chromatography, Affinity; D004295:Dihydroxyphenylalanine; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008543:Melanins / Q000096:biosynthesis; D008544:Melanocytes / Q000166:cytology / Q000201:enzymology; D008562:Membrane Glycoproteins; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010088:Oxidoreductases; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D014443:Tyrosine; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D008543:Melanins; D008562:Membrane Glycoproteins; D011506:Proteins; D014443:Tyrosine; D004295:Dihydroxyphenylalanine; D010088:Oxidoreductases; D014446:Tyrosine 3-Monooxygenase; C489799:TYRP1 protein, human; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase