The process of producing melanin
Melanogenesis is the process of melanin production. Melanocytes are cells that produce and store melanin, particularly at the melanosome (organelle). Melanin refers to a group of pigments produced from the oxidation of tyrosine, followed by polymerization. It is the one responsible for the color of skin, feathers, hair, fur, eyes, scales, etc. There are three basic types of melanin: (1) eumelanin, (2) pheomelanin, and (3) neuromelanin.
The eumelanin is the most common type among the three. The eumelanin may be brown or black in colour. Eumelanin polymer is made up of cross-linked 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) polymers. Eumelanin is produced through a series of catalysed chemical reactions, starting from tyrosine, and with tyrosinase as the key enzyme.
The pheomelanin is a pigment made up of benzothiazine units that is largely responsible for the red pigmentation. Similar to eumelanin, the biosynthesis pathway of pheomelanin begins at tyrosine. It proceeds to the route with an end result of alanyl-hydroxy-benzothiazine in the presence of gluthathione or cysteine.
The neuromelanin is a dark pigment comprised of 5,6-dihydroxyindole monomers. It is made up of a polymer of 5,6-dihydroxyindole monomers. Similar to eumelanin, it is synthesized directly from L-DOPA through the catalytic activity of tyrosine hydroxylase and aromatic acid decarboxylase.