[O2 generation during neuromelanin synthesis. The action of manganese]

The oxygen uptake during the reaction of dopamine autoxidation was studied and it was found that it may occur through two distinct oxidative pathways. One involves the univalent reduction of oxygen, forming the superoxide radical, the other involves a bivalent reduction which generates hydrogen peroxide. The detection of the univalent reaction was followed by the study of oxygen consumption, in the presence of cytochrome c. The detection of the bivalent reaction was made in the presence of catalase. It was found that manganese increases the oxygen uptake of the reaction, by increasing the production of both oxygen active forms. It seems probable that the neurotoxicity of this metal may be related with the increased production of activated oxygen in dopaminergic neurons, which undergo an oxidative stress.