Pyomelanin formation pathway: this route is a bifurcation of the standard L-tyrosine catabolism route. This amino acid undergoes transamination to the corresponding alphaketo acid, and the action of the p-hydroxyphenylpyruvate dioxygenase yields homogentisate (HGA). In the absence of homogentisate dioxygenase activity, the accumulation of HGA provokes the oxidation to the p-quinone form (HGAQ). This oxidation of a p-diphenol to the p-quinone form can be catalyzed by laccases and other oxidase. As in other melanin formation routes, coexistence of reduced and oxidized forms spontaneously react to dimers and finally to ochre-colored polymers (HGA-melanin).