Generation of hydrogen peroxide in the melanin biosynthesis pathway

The generation of H2O2 in the melanin biosynthesis pathway is of great importance because of its great cytotoxic capacity. However, there is controversy concerning the way in which H2O2 is generated in this pathway. In this work we demonstrate that it is generated in a series of chemical reactions coupled to the enzymatic formation of o-quinones by tyrosinase acting on monophenols and o-diphenols and during the auto-oxidation of the o-diphenols and other intermediates in the pathway. The use of the enzymes such as catalase, superoxide dismutase and peroxidase helps reveal the H2O2 generated. Based on the results obtained, we propose a scheme of enzymatic and non-enzymatic reactions that lead to the biosynthesis of melanins, which explains the formation of H2O2.