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Roles of reactive oxygen species in UVA ‐induced oxidation of 5,6‐dihydroxyindole‐2‐carboxylic acid‐melanin as studied by differential spectrophotometric method
Author(s) -
Ito Shosuke,
Kikuta Marina,
Koike Shota,
Szewczyk Grzegorz,
Sarna Michal,
Zadlo Andrzej,
Sarna Tadeusz,
Wakamatsu Kazumasa
Publication year - 2016
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/pcmr.12469
Subject(s) - singlet oxygen , chemistry , photochemistry , reactive oxygen species , melanin , moiety , oxygen , photoprotection , quenching (fluorescence) , superoxide , carboxylic acid , fluorescence , organic chemistry , biochemistry , photosynthesis , physics , quantum mechanics , enzyme
Summary Eumelanin photoprotects pigmented tissues from ultraviolet ( UV ) damage. However, UVA ‐induced tanning seems to result from the photooxidation of preexisting melanin and does not contribute to photoprotection. We investigated the mechanism of UVA ‐induced degradation of 5,6‐dihydroxyindole‐2‐carboxylic acid ( DHICA )‐melanin taking advantage of its solubility in a neutral buffer and using a differential spectrophotometric method to detect subtle changes in its structure. Our methodology is suitable for examining the effects of various agents that interact with reactive oxygen species ( ROS ) to determine how ROS is involved in the UVA ‐induced oxidative modifications. The results show that UVA radiation induces the oxidation of DHICA to indole‐5,6‐quinone‐2‐carboxylic acid in eumelanin, which is then cleaved to form a photodegraded, pyrrolic moiety and finally to form free pyrrole‐2,3,5‐tricarboxylic acid. The possible involvement of superoxide radical and singlet oxygen in the oxidation was suggested. The generation and quenching of singlet oxygen by DHICA ‐melanin was confirmed by direct measurements of singlet oxygen phosphorescence.