Lipoxygenase-catalyzed oxidation of catecholamines.

Dopa and structurally related catecholamines in presence of hydrogen peroxide are oxidized in vitro by soybean lipoxygenase producing the corresponding melanin pigments. The kinetic parameters of the catecholasic reaction, measured as aminochrome formation, have been calculated. The rate of peroxidation depends on catecholamine and hydrogen peroxide concentration. The optimum pH for the peroxidative activity of the enzyme is around 8.5. The enzyme, at higher pH values (pH 9-9.5), is also able to perform an oxidative reaction of the substrates. Implications of the possible biochemical relevance of the reactions are discussed.