Electron transfer properties of melanin. Optimum conditions and the effects of various chemical treatments

Abstract

The optimum conditions for 3 oxidation-reduction reactions of melanin, namely oxidation of NADH, reduction of ferricyanide and a coupled reaction involving oxidation NADH and reduction of ferricyanide, were studied. Experiments in which the pH of the reaction medium was varied showed that rate of oxidation of NADH slightly increased when pH varied from 6.05-8.5, reduction of ferricyanide markedly increased when pH increased from 5.5-8.5 and oxidation of NADH in the coupled reaction increased when pH increased from 5.5-8.5 and reduction of ferricyanide incrased from pH 5.5-7.2. Experiments using varying temperatures showed that rates of all the above reactions increased to varying degrees when temperature increased from 23-45.degree. C; the activation energies for the reactions were calculated. The effects of various treatments of melanin upon the above reactions were studied. Treatment of melanin with oxidizing agents such as KMnO4, benzoquinone, iodine, FeCl3, etc. increased the oxidation of NADH by melanin. Treatment of melanin with the reducing agent ascorbate decreased oxidation of NADH by melanin, and treatment of melanin with KMnO4 decreased reduction of ferricyanide by melanin. The oxidized and reduced forms of melanin may be participating in the reducing and oxidizing activities of melanin.