pheomelaniin

Pheomelanin is one of the two main classes of melanin pigments produced by melanocytes in the skin, hair, and certain feathers and fur. It imparts reddish to yellow hues and contrasts with eumelanin, which provides brown-to-black coloration. The relative amounts of pheomelanin and eumelanin determine an organism's pigmentation and color tone.

Biosynthesis: In melanocytes, melanin synthesis starts from tyrosine via the enzyme tyrosinase. For pheomelanin, dopaquinone reacts with cysteine to form cysteinyldopa, steering the pathway away from eumelanin toward sulfur-containing benzothiazine and benzothiazole polymers. The exact polymer structure is complex; pheomelanin is a sulfur-rich heteropolymer whose formation is influenced by cellular redox state and cysteine availability.

Distribution and phenotype: People with higher pheomelanin content tend to have lighter skin and red hair, especially when eumelanin is low. Variants in the MC1R gene promote pheomelanin production and are strongly associated with red hair color and fair skin.

Function and health implications: Pheomelanin provides color but offers less photoprotection against ultraviolet radiation compared to eumelanin. Under UV exposure, pheomelanin can contribute to the formation of reactive oxygen species, potentially increasing DNA damage and skin cancer risk in susceptible individuals.

Analytical aspects: In research, pheomelanin is quantified using chemical degradation methods and spectroscopic analysis to distinguish it from eumelanin in tissue samples.