title: Isomeric cysteinyldopas provide a (photo)degradable bulk component and a robust structural element in red human hair pheomelanin.
abstract: Alkaline H(2)O(2) degradation of red hair pheomelanin gave, besides 6-(2-amino-2-carboxyethyl)-2-carboxy-4-hydroxybenzothiazole (BTCA), a new product which was identified as 7-(2-amino-2-carboxyethyl)-2-carboxy-4-hydroxybenzothiazole (BTCA-2) originating from 2-S-cysteinyldopa (2SCD) derived units. BTCA-2 was also obtained from a variety of pheomelanic tissues and synthetic pigments. Simultaneous determination of BTCA and BTCA-2 in segments of red hair locks taken at variable distances from the scalp in a group of 19 individuals indicated an abrupt drop of BTCA yields on passing from root to tip, whereas BTCA-2 values remained virtually constant throughout hair length. Analysis of 4-amino-3-hydroxyphenylalanine (AHP) and 3-aminotyrosine (AT) in the same lock segments showed a closely similar trend, whereas yields of thiazole-2,4,5-tricarboxylic acid (TTCA) increased with increasing the distance from the scalp. Prolonged exposure of hair locks to sunlight caused a significant decrease in BTCA-, but not BTCA-2-yielding elements. Finally, model studies showed a substantial degradation of 5SCD-, but not 2SCD-derived units, during pheomelanin synthesis in vitro. It is concluded that red hair pheomelanin consists of a degradable 5SCD-derived bulk component associated with stable 2SCD-derived units. Structural degradation occurs during hair growth probably as a result of oxidative processes related in part to sun exposure.
authors.affiliation: Department of Organic Chemistry and Biochemistry, University of Naples, Naples, Italy.
authors.forename: Giorgia
authors.initials: G
authors.lastname: Greco
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Wakamatsu
authors.forename: Lucia
authors.initials: L
authors.lastname: Panzella
authors.forename: Shosuke
authors.initials: S
authors.lastname: Ito
authors.forename: Alessandra
authors.initials: A
authors.lastname: Napolitano
authors.forename: Marco
authors.initials: M
authors.lastname: d'Ischia
mesh_terms: D052160:Benzothiazoles / Q000737:chemistry / Q000378:metabolism; D003548:Cysteinyldopa / Q000737:chemistry / Q000378:metabolism; D006197:Hair / Q000737:chemistry / Q000378:metabolism; D006200:Hair Color; D006801:Humans; D007536:Isomerism; D008027:Light; D008543:Melanins / Q000737:chemistry* / Q000378:metabolism; D015394:Molecular Structure
chemical_list: D052160:Benzothiazoles; D008543:Melanins; C018362:pheomelanin; D003548:Cysteinyldopa; C051907:4-hydroxybenzothiazole