Humpath.com - Human pathology

Home > A. Molecular pathology > melanin

melanin

Friday 29 October 2004

melanine, melanins

Definition: Melanin is a class of compounds found in the plant, animal and protista kingdoms, where it serves predominantly as a pigment.

Images

- Top-heavy pigment in a naevus (left) with bottom heavy in a melanoma

The class of pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole (also known as hydroquinone), dihydroxyindole carboxylic acid, and their reduced forms.

Another common form of melanin is pheomelanin, a red-brown polymer of benzothiazine units largely responsible for red hair and freckles.

The presence of melanin in the archaea and bacteria kingdoms is an issue of ongoing debate amongst researchers in the field.

Types

- eumelanin
- pheomelanin
- neurmelanin

Melanogenesis

The increased production of melanin in human skin is called melanogenesis. It is stimulated by the DNA damages that are caused by UVB-radiation, and it leads to a delayed development of a tan. This melanogenesis-based tan takes more time to develop, but it is long lasting.

Photoprotections

The photochemical properties of melanin make it an excellent photoprotectant. It absorbs harmful UV-radiation and transforms the energy into harmless amounts of heat through a process called "ultrafast internal conversion". This property enables melanin to dissipate more than 99.9% of the absorbed UV radiation as heat and it keeps the generation of free radicals at a minimum (see photoprotection). This prevents the indirect DNA damage which is responsible for the formation of malignant melanoma.