title: Fibroblasts co-expressing tyrosinase and the b-protein synthesize both eumelanin and phaeomelanin.
abstract: Melanin synthesis in the mouse involves the interaction of many pigmentation loci. Tyrosinase, the product of the albino (c) locus, catalyses the first step of the pathway. The brown (b) locus protein has significant homology to tyrosinase and controls black/brown coat coloration, but its function is controversial. To investigate the function of the b-protein and its interaction with tyrosinase, we established cell lines expressing both tyrosinase and the b-protein by transfecting tyrosinase-expressing fibroblasts with a b-protein expression vector. The tyrosinase-expressing parent line does not have L-dopachrome tautomerase activity, but this enzyme is detectable in double transfectants as well as in fibroblasts expressing the b-protein alone. Cells expressing both proteins have a higher steady-state level of tyrosinase than fibroblasts expressing tyrosinase alone, and contain elevated levels of melanin intermediates. This is thought to result from interaction of tyrosinase with the b-protein. Only phaeomelanin is detectable in fibroblasts expressing tyrosinase alone, whereas double transfectants synthesise significantly more phaeomelanin and detectable eumelanin.
authors.affiliation: Sir William Dunn School of Pathology, Oxford University, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Winder
authors.forename: G
authors.initials: G
authors.lastname: Odh
authors.forename: E
authors.initials: E
authors.lastname: Rosengren
authors.forename: H
authors.initials: H
authors.lastname: Rorsman
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002396:Catechols / Q000032:analysis; D002999:Clone Cells; D003470:Culture Media / Q000737:chemistry; D019746:Intramolecular Oxidoreductases; D007535:Isomerases / Q000378:metabolism*; D008543:Melanins / Q000096:biosynthesis* / Q000737:chemistry; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010088:Oxidoreductases; D014162:Transfection; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D002396:Catechols; D003470:Culture Media; D008543:Melanins; D008562:Membrane Glycoproteins; C016042:phaeomelanin; C041877:eumelanin; D010088:Oxidoreductases; D014446:Tyrosine 3-Monooxygenase; C079621:Tyrp1 protein, mouse; D014442:Monophenol Monooxygenase; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase