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Citation
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HERO ID
483057
Reference Type
Journal Article
Subtype
Review
Title
Chemistry of mixed melanogenesis - Pivotal roles of dopaquinone
Author(s)
Ito, S; Wakamatsu, K
Year
2008
Is Peer Reviewed?
1
Journal
Photochemistry and Photobiology
ISSN:
0031-8655
EISSN:
1751-1097
Volume
84
Issue
3
Page Numbers
582-592
Language
English
PMID
18435614
DOI
10.1111/j.1751-1097.2007.00238.x
Abstract
Melanins can be classified into two major groups-insoluble brown to black pigments termed eumelanin and alkali-soluble yellow to reddish-brown pigments termed pheomelanin. Both types of pigment derive from the common precursor dopaquinone (ortho-quinone of 3,4-dihydroxyphenylalanine) which is formed via the oxidation Of L-tyrosine by the melanogenic enzyme tyrosinase. Dopaquinone is a highly reactive ortho-quinone that plays pivotal roles in the chemical control of melanogenesis. In the absence of sulfhydryl compounds, dopaquinone undergoes intramolecular cyclization to form cyclodopa, which is then rapidly oxidized by a redox reaction with dopaquinone to give dopachrome (and dopa). Dopachrome then gradually and spontaneously rearranges to form 5,6-dihydroxyindole and to a lesser extent 5,6-dihydroxyindole-2-carboxylic acid, the ratio of which is determined by a distinct melanogenic enzyme termed dopachrome tautomerase (tyrosinase-related protein-2). Oxidation and subsequent polymerization of these dihydroxyindoles leads to the production of eumelanin. However, when eysteine is present, this process gives rise preferentially to the production of cysteinyldopa isomers. Cysteinyldopas are subsequently oxidized through redox reaction with dopaquinone to form cysteinyldopaquinones that eventually lead to the production of pheomelanin. Pulse radiolysis studies of early stages of melanogenesis (involving dopaquinone and cysteine) indicate that mixed melanogenesis proceeds in three distinct stages-the initial production of cysteinyldopas, followed by their oxidation to produce pheomelanin, followed finally by the production of eumelanin. Based on these data, a casing model of mixed melanogenesis is proposed in which a preformed pheomelanic core is covered by a eumelanic surface.
Keywords
cultured human melanocytes; hair follicular melanocytes; tyrosinase-related protein; dhica oxidase activity; pulse-radiolysis; melanoma-cells; metal-ions; red hair; chemical characterization; dopachrome tautomerase
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