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23 February 2009 Structural characterization of colored human iridal melanosomes by photo emission electron microscopy
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Ocular uveal melanosomes contain both eumelanin and pheomelanin. The ratio of these two melanins has been discussed in relation to the epidemiological data for skin cancer rates, with increased incidence observed for increased relative concentrations of pheomelanin. Recent studies suggest that a similar trend exists underlying the epidemiology of uveal melanomas. In the present study, the biomolecular organization of human iridal melanosomes from different colored irises were examined to determine if the photoreactivity changes with the altered eumelanin:pheomelanin ratio, and whether such changes can account for epidemiological results. Specifically, photoemission electron microscopy (PEEM), a unique surface-sensitive, direct-imaging technique capable of providing chemical information not obtained by other electron microscopies, was used in combination with Duke University's tunable UV free electron laser (FEL) to determine the surface electrochemical properties of melanosomes from blue and dark brown irides. The results demonstrate that the melanins are organized such that pheomelanin is encased by eumelanin. This "casing model" is consistent with kinetic information available on the early steps of melanogenesis and provides new insights into molecular mechanisms underlying the epidemiology of uveal melanoma.
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Dana N. Peles, Lian Hong, John D. Simon, and Dan-Ning Hu M.D. "Structural characterization of colored human iridal melanosomes by photo emission electron microscopy", Proc. SPIE 7182, Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues VII, 71820E (23 February 2009);

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