Eumelanins granules

There are distinct chemical properties of eumelanin and pheomelanin which affect the physiochemical properties of hair. - Pheomelanin granules are smaller and less resistant to chemical degradation than eumelanin granules. Pheomelanin is soluble in dilute alkali in comparison to eumelanin, which is insoluble in almost all solvents. Pheomelanin and eumelanin also differ in sulfur content. Pheomelanin is high in sulfur content (9 to 12%) in contrast to eumelanin, which contains only 0 to 1% sulfur. ... 

Melanin granules are secreted by melanocytes in the hair papilla and distributed to keratin in the hair cortex and inner layers of the hair sheath during normal development. Melanogenesis is subject to hormonal control and has been the focus of intensive genetic studies. Two main forms of melanin exist in human skin—eumelanin and phaeomelanin, both of which are derived from tyrosine through the action of tyrosinase (a cupro-enzyme) and possibly other key enzymes (with nickel, chromium, iron, and manganese as cofactors). Tyrosine is converted to dihydroxyphenylalanine and, via a series of intermediate steps, to indole-5,6-quinone, which polymerizes to eumelanin. Phaeomelanins are produced by a similar mechanism but with the incorporation of sulfur (as cysteine) by a nonenzymatic step in the oxidation process. 

Blond hair contains elliptical and oval melanosomes. The granules in melanosomes are small, few in number, and likely represent eumelanin, although pheomelanin also may be present in blond hair. T22,24 Ortonne and Prota suggested that blond hair results from a quantitative decrease in the synthesis of melanin in comparison to black and brown hair. The main features which distinguish brown hair from blond hair are the presence of more melanosomes and a higher concentration of melanin in brown hair. - Melanosomes present in the shaft of blond hair also appear to be more susceptible to degradation than melanosomes in black hair. Cesarini reported that melanosomes may not be present in the shaft of blond hair, possibly due to digestion of melanosomes by lysosomes. 

Pheomelanins are the yellow-red pigments and are lighter in color than the brown-black pigments of human hair. Both pheomelanins and eumelanins occur as granules in melanocytes. Prota and co-workers [14,62] have proposed that red hair pigments are formed by a modihcation of the eume-lanin pathway described earlier. The pheomelanin pathway, however, involves the interaction of cysteine with dopaquinone. Figure 4-28 summarizes Prota s [62] description of a common metabolic pathway for formation of all melanins and shows how pheomelanin formation relates to eumelanin biosynthesis. 

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