The Red and the Black
Top Cited Papers
- 24 August 2010
- journal article
- review article
- Published by American Chemical Society (ACS) in Accounts of Chemical Research
- Vol. 43 (11), 1452-1460
- https://doi.org/10.1021/ar100079y
Abstract
“Pigmentation, which is primarily determined by the amount, the type, and the distribution of melanin, shows a remarkable diversity in human populations, and in this sense, it is an atypical trait.”—E. J. Parra. Melanin is found throughout the human body, skin, eye, brain, hair, and inner ear, yet its molecular structure remains elusive. Researchers have characterized the molecular building blocks of melanin but have not been able to describe how those components fit together in the overall architecture of the pigment. Melanin is categorized into two distinct classes, pheomelanin (red) and eumelanin (black). Although these classes share a common biosynthetic origin, specific molecular reactions occurring early in pigment production differentiate these two types. Pure eumelanin is found throughout nature, which has allowed researchers to characterize and quantify its chemical properties. However, pure pheomelanin is not observed in nature and rarely makes up more than ∼25% of the total melanin present. In this Account, we explore our current understanding of the structure and reactivity of the red and black pigments. Epidemiological studies of skin and ocular cancers suggest that increasing relative proportions of pheomelanin correlate with increased risk factors for these diseases. Therefore, understanding the factors that control the relative abundance of the two pigments has become increasingly important. Consequently, researchers have worked to elucidate the chemistry of pheomelanin to determine whether the pigment could cause these cancers and, if so, by what mechanisms. The photoactivation of oxygen by pheomelanin in the UV-A range could contribute to the development of UV-induced cancers: recent measurement of the surface photoionization threshold of intact melanosomes reveals a lower photoionization potential for pheomelanin than eumelanin. A complementary study of intact human melanosomes isolated from different colored irides reveals that the absorption coefficient of the melanosome decreases with increasing pheomelanin content. These results suggest that the epidemiological data may simply result from an increased exposure of the underlying tissues to UV light.This publication has 48 references indexed in Scilit:
- Direct Measurement of the Ultraviolet Absorption Coefficient of Single Retinal MelanosomesPhotochemistry and Photobiology, 2010
- Human Iridal Stroma Melanosomes of Varying Pheomelanin Contents Possess a Common Eumelanic Outer SurfaceThe Journal of Physical Chemistry B, 2009
- Comparison of eumelanin and pheomelanin content between cultured uveal melanoma cells and normal uveal melanocytesMelanoma Research, 2009
- Insights into Melanosomes and Melanin from Some Interesting Spatial and Temporal PropertiesThe Journal of Physical Chemistry B, 2008
- The surface oxidation potential of human neuromelanin reveals a spherical architecture with a pheomelanin core and a eumelanin surfaceProceedings of the National Academy of Sciences of the United States of America, 2006
- Photoionization Thresholds of Melanins Obtained from Free Electron Laser‐Photoelectron Emission Microscopy, Femtosecond Transient Absorption Spectroscopy and Electron Paramagnetic Resonance Measurements of Oxygen PhotoconsumptionPhotochemistry and Photobiology, 2006
- A Chemist's View of MelanogenesisPigment Cell Research, 2003
- Explanation for the Disparity among Absorption and Action Spectra of EumelaninThe Journal of Physical Chemistry B, 1999
- (Pheo)Melanin Photosensitizes UVA-Induced DNA Damage in Cultured Human MelanocytesJournal of Investigative Dermatology, 1998
- Efficient synthesis of 5,6-diacetoxyindole: a stable eumelanin precursorThe Journal of Organic Chemistry, 1985