Stimulatory and inhibitory effects of manganous and ferrous ions on epinephrine oxidation.

Low concentrations of manganous ions stimulate the oxidation of epinephrine to adrenochrome by rat liver microsomes, or by isolated NADPH-cytochrome c reductase, 4 fold. In contrast, much higher manganous ion concentrations are required for the chemical oxidation of epinephrine. Whereas the microsomal manganese stimulated epinephrine oxidation is inhibited by Superoxide dismutase, as is the nonstimulated enzymatic oxidation, Superoxide dismutase has no inhibitory effect on the oxidation of epinephrine in the absence of enzymes.Ferrous ions inhibit the manganous ion stimulated chemical oxidation of epinephrine more effectively than the similarly stimulated enzymatic oxidation of epinephrine. Based upon these observations different mechanisms for chemical and enzymatic manganous ion-induced epinephrine oxidation are suggested. Furthermore, possible implications of the metal ion-stimulated or inhibited oxidation of catechols in vivo are discussed.