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Isomeric cysteinyldopas provide a (photo)degradable bulk component and a robust structural element in red human hair pheomelanin
Author(s) -
Greco Giorgia,
Wakamatsu Kazumasa,
Panzella Lucia,
Ito Shosuke,
Napolitano Alessandra,
D’Ischia Marco
Publication year - 2009
Publication title -
pigment cell and melanoma research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.618
H-Index - 105
eISSN - 1755-148X
pISSN - 1755-1471
DOI - 10.1111/j.1755-148x.2009.00561.x
Subject(s) - chemistry , scalp , degradation (telecommunications) , amino acid , biophysics , biochemistry , stereochemistry , biology , anatomy , telecommunications , computer science
Summary 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.