Raper-Mason pathway for eu- and pheomelanin formation. The initial phase until L-dopaquinone is common to pheomelanin and eumelanin. It consists in the oxidation of L-tyrosine catalyzed by the two activities of tyrosinase, tyrosine hydroxylase, and dopa oxidase. L-Dopaquinone is the pivotal intermediate. Addition of L-cysteine gives place to benzothiazine units and then to pheomelanins (right). In the absence of L-cysteine, eumelanogenesis takes place since L-dopaquinone spontaneously cycled to L-leukodopachrome. This indoline reacts with L-dopaquinone in a very fast spontaneous reaction to yield L-dopachrome. L-Dopachrome is converted to DHI and DHICA mixtures, according to Trp2 activity and decarboxylation rate. Further oxidation of these dihydroxyindoles by tyrosinase or Trp1 gives place to indolequinones; subsequent crosslink reactions between hydroxy and quinone forms lead to the polymer. In this final phase of polymerization, the Pmel17 protein located in the eumelanosome seems to have a role in the regulation and deposition of the polymer on that organelle.