Aggregation of eumelanin mitigates photogeneration of reactive oxygen species

J. Brian Nofsinger, Yan Liu, John D. Simon

Research output: Contribution to journalArticle

63 Citations (Scopus)

Abstract

Melanins protect tissue by absorption and rapid nonradiative, nonreactive dissipation of ultraviolet (UV) light. However, melanins also produce reactive oxygen species (ROS) upon UV illumination. A chemical understanding of this dichotomy of photoprotection and phototoxicity has not been established. Herein this issue is examined by studying the UV-B induced oxidation and reduction of cytochrome c by ROS generated by different aggregation states of eumelanin. The quantum yield for superoxide anion by unaggregated oligomers is 7.4 × 10-3, an order of magnitude greater than that characteristic of the bulk pigment. The quantum efficiency of hydrogen peroxide production by oligomers is 5.7 × 10-3, and its production is attributed to reaction between superoxide anion and hydroquinone groups on eumelanin oligomers. Aggregation of oligomers results in a reduction of these quantum yields, having a significantly greater effect on the efficiency of hydrogen peroxide production. This effect is attributed to the decrease in surface concentration of hydroquinone sites upon aggregation. The effect of aggregation on the photogeneration of ROS serves to provide a foundation for the understanding of the dichotomy of photoprotective and phototoxic properties of melanin.

Original languageEnglish
Pages (from-to)720-730
Number of pages11
JournalFree Radical Biology and Medicine
Volume32
Issue number8
DOIs
Publication statusPublished - Apr 15 2002

Fingerprint

Melanins
Oligomers
Reactive Oxygen Species
Agglomeration
Superoxides
Hydrogen Peroxide
Quantum yield
Phototoxic Dermatitis
Ultraviolet Rays
Cytochromes c
Lighting
Oxidation-Reduction
Quantum efficiency
Pigments
Tissue
Oxidation
eumelanin
hydroquinone

Keywords

  • Free radicals
  • Hydrogen peroxide
  • Melanin
  • Melanogenesis
  • Photoprotection
  • Superoxide anion

ASJC Scopus subject areas

  • Medicine(all)
  • Toxicology
  • Clinical Biochemistry

Cite this

Aggregation of eumelanin mitigates photogeneration of reactive oxygen species. / Nofsinger, J. Brian; Liu, Yan; Simon, John D.

In: Free Radical Biology and Medicine, Vol. 32, No. 8, 15.04.2002, p. 720-730.

Research output: Contribution to journalArticle

Nofsinger, J. Brian ; Liu, Yan ; Simon, John D. / Aggregation of eumelanin mitigates photogeneration of reactive oxygen species. In: Free Radical Biology and Medicine. 2002 ; Vol. 32, No. 8. pp. 720-730.
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