RT Journal Article SR Electronic T1 Oxidative Pathways for Catecholamines in the Genesis of Neuromelanin and Cytotoxic Quinones JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 633 OP 643 VO 14 IS 4 A1 DOYLE G. GRAHAM YR 1978 UL http://molpharm.aspetjournals.org/content/14/4/633.abstract AB The autoxidation, periodate oxidation, and tyrosinase-mediated oxidation of 6-hydroxydopamine, dopamine, norepinephrine, and epinephrine were studied by absorption spectroscopy. Autoxidation and tyrosinase-mediated oxidation of the three catecholamines resulted in dopachrome analogues—aminochrome from dopamine, noradrenochrome from norepinephrine, and adrenochrome from epinephrine—without evidence for the expected intermediates, the o-quinones and the corresponding leukochromes. The use of periodate as an oxidant, on the other hand, allowed visualization of the o-quinone intermediates and the subsequent conversion to the dopachrome analogues. Cyclization of the o-quinones appeared to occur in the order epinephrine > norepinephrine > dopamine, while the rate of autoxidation occurred in the reverse order. The oxidation of 6-hydroxydopamine to its p-quinone was visualized under all three oxidizing conditions. However, the oxidation of 6-hydroxydopamine by periodate gave evidence for a transient intermediate, the o-quinone, which rapidly tautomerized to the p-quinone. The p-quinone product of 6-hydroxydopamine was seen to undergo cyclization to aminochrome, with subsequent polymerization.