Spin-trapping free radicals in the autooxidation of 6-hydroxydopamine

Author(s): Floyd RA, Wiseman BB

Abstract

Utilizing the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide, and we h ave demonstrated that hydroxyl free radicals are produced during the alkaline (pH 11.5) autooxidation of 6-hydroxydopamine. The amount of trapped hydroxyl free radical is essentially a linear function of the initial 6-hydroxydopamine concentration up to 2 mM. The iron chelators, diethylenetriamine pentaacetic acid and deferoxamine, considerably reduced the amount of trapped hydroxyl free radical. Catalase and superoxide dismutase were also effective in reducing the amount of hydroxyl free radical spin trapped. Oxygen was absolutely essential for autooxidation of 6-hydroxydopamine and also for formation of the hydroxyl free radical. The semiquinone free radical of 6-hydroxydopamine was present to a small extent in the absence of oxygen. Deferoxamine was effective in lowering the amount of semiquinone radical formed anaerobically, thus suggesting iron was in part responsible for oxidation of 6-hydroxydopamine. The semiquinone free radical yielded an electron spin resonance spectrum characterized by the free electron coupling to four protons having the following coupling constants: H1 ≈ H2 = 2.95 gauss, H3 ≈ 1.1 gauss and H4 ≈ 0.6 gauss.

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