Interaction of melanin with oxygen

The effect of melanin on oxygen consumption was studied considering: the type of melanin (synthetic vs natural); alteration of the chemical structure of melanin (oxidation, reduction, or methylation of synthetic melanin and acid hydrolysis of natural melanin); pH; illumination by visible light; presence of catalase. Each factor affected the rate of oxygen consumption in complex and interrelated ways. Many of the results are consistent with oxygen consumption resulting from direct reaction with hydroquinone and semiquinone subunits of the polymer. Some of the data, however, indicate that other mechanisms must also be important. In particular, treatments that should have greatly reduced the number of hydroquinone subunits (methylation and oxidation by ferricyanide) had only small inhibitory effects on oxygen consumption. There is an apparent relationship between the square of the concentration of induced radicals and oxygen consumption.