CHEMILUMINESCENCE IN THE OXIDATION OF 6-HYDROXYDOPAMINE: EFFECTS OF LUCIGENIN, SCAVENGERS OF ACTIVE OXYGEN, METAL CHELATORS AND THE PRESENCE OF OXYGEN

Abstract— Maximum chemiluminescence in a system containing 6-hydroxydopamine (6-OHDA) and H₂O₂ required the addition of Fe²⁺:EDTA, oxygen, and lucigenin. In this system luminescence was strongly inhibited by catalase (91% inhibition) or 50 m M mannitol (83%), whereas superoxide dismutase or ascorbate did not significantly change the reaction rate. In the absence of lucigenin, 50 m M mannitol (78%), catalase (76%), or ascorbate (73%) inhibited strongly, while superoxide dismutase inhibited by 60%. Removing EDTA from the lucigenin-containing system caused a 79% decrease in luminescence, while the substitution of desferoxamine for EDTA decreased luminescence by 55%. In the presence of desferoxamine plus EDTA the luminescence increased by 30% in comparison with that seen with EDTA alone. Luminescence in the system containing 6-hydroxydopamine, H₂O₂, Fe²⁺:EDTA and lucigenin required the presence of oxygen (93% inhibition anaerobically), consistent with a mechanism involving reductive oxygenation of the lucigenin. It is concluded that luminescence in the presence of lucigenin involves a substantial contribution from H₂O₂ and Fe²⁺ mediated by a mannitol-sensitive intermediate (conceivably Fenton-derived hydroxyl radicals). In the absence of lucigenin, superoxide and an ascorbate-labile component are additional important participants in the process.