Malanin

Melanin is a broad term for a group of natural pigments found in most organisms. Melanin is produced by the oxidation of the amino acid tyrosine, followed by polymerization. The melanin pigments are produced in a specialized group of cells known as melanocytes.

There are three basic types of melanin: eumelanin, pheomelanin, and neuromelanin. The most common type is eumelanin, of which there are two types—brown eumelanin and black eumelanin. Pheomelanin is a cysteine-containing red polymer of benzothiazine units largely responsible for red hair and freckles. Neuromelanin is found in the brain, though its function remains obscure.

Production and Function

In the human skin, melanogenesis is initiated by exposure to UV radiation, causing the skin to darken. Melanin is an effective absorber of light; the pigment is able to dissipate over 99.9% of absorbed UV radiation. Because of this property, melanin is thought to protect skin cells from UVB radiation damage, reducing the risk of cancer, and it is considered that exposure to UV radiation is associated with increased risk of malignant melanoma, a cancer of melanocytes (melanin cells).

Role in Human Adaptation

Melanin controls the amount of ultraviolet (UV) radiation from the sun that penetrates the skin by absorption. While UV radiation can assist in the production of vitamin D, excessive exposure to UV can damage health.

Disorders and Diseases

Disorders of melanin pigmentation can be divided into hypopigmentation (too little melanin) and hyperpigmentation (too much melanin). Some forms of albinism, for example, are characterized by a lack of melanin production. Melanoma, a potentially deadly skin cancer, is related to uncontrolled proliferation of melanocytes, the cells that produce melanin.

See Also

• Melanocyte
• Melanoma
• Albinism
• Vitiligo