%0 Journal Article
%T Melanins: Skin Pigments and Much More¡ªTypes, Structural Models, Biological Functions, and Formation Routes
%A F. Solano
%J New Journal of Science
%D 2014
%R 10.1155/2014/498276
%X This review presents a general view of all types of melanin in all types of organisms. Melanin is frequently considered just an animal cutaneous pigment and is treated separately from similar fungal or bacterial pigments. Similarities concerning the phenol precursors and common patterns in the formation routes are discussed. All melanins are formed in a first enzymatically-controlled phase, generally a phenolase, and a second phase characterized by an uncontrolled polymerization of the oxidized intermediates. In that second phase, quinones derived from phenol oxidation play a crucial role. Concerning functions, all melanins show a common feature, a protective role, but they are not merely photoprotective pigments against UV sunlight. In pathogenic microorganisms, melanization becomes a virulence factor since melanin protects microbial cells from defense mechanisms in the infected host. In turn, some melanins are formed in tissues where sunlight radiation is not a potential threat. Then, their redox, metal chelating, or free radical scavenging properties are more important than light absorption capacity. These pigments sometimes behave as a double-edged sword, and inhibition of melanogenesis is desirable in different cells. Melanin biochemistry is an active field of research from dermatological, biomedical, cosmetical, and microbiological points of view, as well as fruit technology. 1. Antecedents, Concept, Types, and Occurrence Melanin is the generic name used to refer to perhaps the most ubiquitous, resistant, heterogeneous, and ancient pigments found in nature. Melanin appeared very early in most living kingdoms on the Earth. Thus, melanin has been recently found in very old fossils from dinosaurs, early birds, nonavian theropod species [1, 2], and primitive cephalopods [3]. These recent findings will probably make melanin a new biomarker in life evolution. The name ¡°melanin¡± comes from the ancient Greek melanos, meaning ¡°dark,¡± and, according to Borovansky [4], the term was probably first applied by the Swedish chemist Berzelius in 1840 to call a dark pigment extracted from eye membranes [5]. However, first references of human skin pigmentation and somehow to the existence of melanin without using the current name are very old. Pharaonic medicine in the Ebers Papyrus (1550 BC) described some diseases affecting skin color [6], and one of them was probably vitiligo, although that term appeared much later, derived from the Latin word ¡°vitellus¡± meaning ¡°veal¡± or pale pink skin [7]. The first relatively detailed written description on skin pigmentation
%U http://www.hindawi.com/journals/njos/2014/498276/