Oxidation potentials of human eumelanosomes and pheomelanosomes

Alexander Samokhvalov, Lian Hong, Yan Liu, Jacob Garguilo, Robert J. Nemanich, Glenn S. Edwards, John D. Simon

Research output: Contribution to journalArticlepeer-review

70 Scopus citations


Eumelanosomes and pheomelanosomes isolated from black and red human hair, respectively, were studied by photoelectron emission microscopy (PEEM). PEEM images were collected at various wavelengths between 207 and 344 nm, using the spontaneous emission output of the Duke OK-4 free electron laser (FEL). Analysis of the FEL-PEEM data revealed ionization thresholds of 4.6 and 3.9 eV corresponding to oxidation potentials of -0.2 and +0.5 V vs normal hydrogen electrode for eumelanosomes and pheomelanosomes, respectively. The difference in oxidation potential is attributed to the pigment content of the melanosome, namely whether it contains primarily eumelanin and pheomelanin. The effect of added melanosomes on the reduction of Fe(III)-cytochrome showed pheomelanosomes are stronger reducing agents than eumelanosomes, consistent with the measured oxidation potentials. The FEL-PEEM experiment offers to be an important new approach for quantifying the effects of age, oxidation and metal accumulation on the oxidation potentials of intact melanosomes.

Original languageEnglish (US)
Pages (from-to)145-148
Number of pages4
JournalPhotochemistry and photobiology
Issue number1
StatePublished - Jan 1 2005
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry


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