Melanin is used in the skin of zebrafish for camouflage, mimicry, communication and protection from the sun. It is also a pigment in the eyes. Melanin is produced by melanocytes, organelles within the skin cells. Eumelanins are brown and black pigments, while other melanins exist, pheomelanin being yellow and red pigments, and neuromelanin being used in the brain. All of these pigments require tyrosine to start their synthesis. To start this pathway, tyrosine is transported into the melanosome by an amino acid transporter, and at this point it is metabolized to L-dopachrome . Within the melanosome membrane, L-dopachrome tautomerase converts L-dopachrome to 5,6-dihydroxyindole-2-carboxylic acid. This then interacts with tyrosinase-related protein 1a, which adds an oxygen molecule to form 5,6-indolequinone-2-carboxylic acid. This then undergoes a final reaction to form eumelanin. Alternatively, L-dopachrome can spontaneously lose a carbon dioxide molecule, forming 5,6-dihydroxyindole. Following this, it can interact with tyrosinase to form indole-5,6-quinone. Finally, another reaction occurs, forming eumelanin from this compound.

Melanin Biosynthesis References