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melanin
Pronunciation (mel′ă-nin)
- Any of the dark brown to black polymers of indole-5,6-quinone and/or 5,6-dihydroxyindole 2-carboxylic acid that normally occur in the skin, hair, pigmented coat of the retina, and inconstantly in the medulla and zona reticularis of the adrenal gland. Melanin may be formed in vitro or biologically by oxidation of l-tyrosine or l-tryptophan, the usual mechanism being the enzymatic oxidation of l-tyrosine to 3,4-dihydroxy-l-phenylalanine (dopa) and dopaquinone by monophenol monooxygenase, and the further oxidation (probably spontaneous) of this intermediate to melanin. Cf.: eumelanin, pheomelanin
Syn: melanotic pigment
[G. melas (melan-), black]
WebMD Medical Reference from "Stedman's Medical Dictionary"
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Stedman’s Medical Dictionary 28th Edition, Copyright© 2006_Lippincott Williams & Wilkins. All rights reserved.
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