melanin

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melanin

(mĕl`ənĭn), water-insoluble polymer of various compounds derived from the amino acid tyrosinetyrosine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
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. It is one of two pigments found in human skin and hair and adds brown to skin color; the other pigment is carotenecarotene
, long-chained, unsaturated hydrocarbon found as a pigment in many higher plants, particularly carrots, sweet potatoes, and leafy vegetables. Carotene is thought to assist in trapping light energy for photosynthesis or to aid in chemical reduction.
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, which contributes yellow coloring. The synthesis of melanin reactions is catalyzed by the enzyme tyrosinase; an inherited lack of tyrosinase activity results in one of the forms of albinism. Tyrosinase is found in only one specialized type of cell, the melanocyte, and in this cell melanin is found in membrane-bound bodies called melanosomes. Melanosomes can be transferred from their site of synthesis in the melanocytes to other cell types. The various hues and degrees of pigmentation found in the skin of human beings are directly related to the number, size, and distribution of melanosomes within the melanocytes and other cells. Besides it role in pigmentation, melanin, which absorbs ultraviolet light, plays a protective role when skin is exposed to the damaging rays of the sun (see sunburnsunburn,
inflammation of the skin caused by actinic rays from the sun or artificial sources. Moderate exposure to ultraviolet radiation is followed by a red blush, but severe exposure may result in blisters, pain, and constitutional symptoms.
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; skin cancerskin cancer,
malignant tumor of the skin. The most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma. Rarer forms include mycosis fungoides (a type of lymphoma) and Kaposi's sarcoma.
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).

melanin

[′mel·ə·nən]
(biochemistry)
Any of a group of brown or black pigments occurring in plants and animals.

melanin

any of a group of black or dark brown pigments present in the hair, skin, and eyes of man and animals: produced in excess in certain skin diseases and in melanomas
References in periodicals archive ?
Three such lesions, replete with neuromelanin, have been described in the medical literature.
There is little or no neuromelanin in the substantia nigra of rodents, they point out, while humans and monkeys have large amounts of the pigment in the substantia nigra.
Although the pigmented locus ceruleus region of the brain also contains neuromelanin, it is largely immune to the cell-destroying effects of low doses of MPTP.
It looks like neuromelanin greatly assists in the killing of brain cells.
This pigment was non-acid fast and negative for periodic acid-Schiff, thereby ruling out the possibility of lipofuscin and neuromelanin.
Clinical Features of Pigmented Astrocytic Tumors Age Duration of Source, y y/Sex Clinical Features Symptoms, y Soffer et al,[16] 1992 17/F Epilepsy 5 Vajtai et al,[17] 1996 41/F Psychomotor seizures 24 Kanzawa et al,[18] 1997 47/M Psychomotor seizures 8 Present case 32/M Partial complex seizures 2 Diagnosis Nature of Source, y Pigment Softer et al,[16] 1992 Ganglioglioma Melanin Vajtai et al,[17] 1996 Pilocytic astrocytoma Neuromelanin Kanzawa et al,[18] 1997 Pleomorphic xanthoastrocytoma Melanin Present case Pleomorphic xanthoastrocytoma Melanin
Neuromelanin is produced and stored by neurons involved in catecholamine synthesis.