Figure 2: Biosynthetic pathway of melanin. Melanin is present in two main forms: (1) the highly ultraviolet-protective brown/black “eumelanin” pigment, and (2) the ultraviolet-permeable red/blonde “pheomelanin.” Eumelanin and pheomelanin are both synthesized from tyrosine, an amino acid. Tyrosinase, the enzyme that catalyzes the synthetic rate-limiting reaction for both types of melanin, is the deficient enzyme in the most common type of albinism. The incorporation of a cysteine into pheomelanin leads to the retention of a moiety of sulfur into the pigment, which can contribute to oxidative injury caused by ultraviolet. D'Orazio et al. (DOPA: 3,4-dihydroxyphenylalanine, DHI: 5,6-dihydroxyindole, DHICA: 5,6-dihydroxyindole-2-carboxylic acid).