Melanin

This is the common name of black and dark brown pigments. They are present in hair, skin, and retina, where they form complexes with proteins, as well as in freckles, some skin tumors. Their molecules are complex polymeric complexes of derivatives of tyrosine and phenylalanine and proteins. In the vertebrate body, they are formed in melanocytes and melanophores (filling of melanosomes in the matrix), catalyzed by tyrosinase, located in mitochondria. Together with carotenoids, pterins, and others, they participate in adapting to light. Melanin protects warm-blooded animals from the effects of light, participates in regulating body temperature. It is formed more in the skin when exposed to ultraviolet radiation (sunburn, freckles). Melanins accumulate in specialized cells called melanophores. Cells producing melanins can promote tumors – melanomas. When melanin synthesis is interrupted, hair grays. Melanin synthesis is related to the activity of endocrine glands. Therefore, disturbances in their function (Addison’s disease, hyperthyroidism, hypopituitarism), as well as changes in skin pigmentation during pregnancy. The formation of melanin is regulated by α- and β-melanotropins, as well as thyroid, steroid, and sex hormones, and others. Their synthesis can also be activated by X-ray radiation, arsenic, silver, bismuth through the diphenoloxidase reaction. When normal pigmentation does not occur in the skin, albinism forms in the retina.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė