IDENTIFICATION OF CATECHOL-PROTEIN CONJUGATES IN NEOSTRIATAL SLICES INCUBATED WITH [H-3] DOPAMINE - IMPACT OF ASCORBIC-ACID AND GLUTATHIONE

There is evidence to suggest that degeneration of dopaminergic neurons in Parkinson's disease and certain other conditions results from the action of reactive species generated during the oxidation of dopamine. We, therefore, have begun to explore the conditions under which such reactive species are formed. Tissue slices prepared from rat neostriat um were incubated in a standard Krebs bicarbonate buffer for up to 120 min. In the presence of [H-3]dopamine (0.01-100 mu M), binding of tri tium to the acid-insoluble protein fraction was detected. Binding was attenuated by the addition of ascorbate (0.085-0.85 mM) or glutathione (0.01-1.0 mM) to the buffer. Acid hydrolysis of the protein revealed the presence of cysteinyl-dopamine and cysteinyl-dihydroxyphenylacetic acid residues. These results suggest that dopamine oxidizes to form r eactive metabolites, presumably quinones, that then bind to nucleophil ic sulfhydryl groups on protein cysteinyl residues. The findings furth er suggest that the extent to which reactive metabolites are formed is determined in part by the balance between the availability of dopamin e and the antioxidant environment.