Oxidative pathways for catecholamines in the genesis of neuromelanin and cytotoxic quinones
Graham, D.G.
Molecular Pharmacology 14(4): 633-643
1978
ISSN/ISBN: 0026-895X PMID: 98706 Document Number: 128522
The autoxidation, periodate oxidation and tyrosinase-mediated [mushroom tyrosinase, EC 1.10.3.1.] oxidation of 6-hydroxydopamine, dopamine, norepinephrine and epinephrine were studied by absorption spectroscopy. Autoxidation and tyrosinase-mediated oxidation of the 3 catecholamines resulted in dopachrome analogs, 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, allowed visualization of the o-quinone intermediates and the subsequent conversion to the dopachrome analog. Cyclization of the o-quinones appeared to occur in the order epinephrine > norepinephrine > dopamine, while the rate of autoxidation occurred in reverse order. The oxidation of 6-hydroxydopamine to its p-quinone was visualized under all 3 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 underwent cyclization to aminochrome, with subsequent polymerization.