ascorbic-acid and 6-hydroxydopa-quinone

Bovine dopamine beta-hydroxylase (DbH) was inactivated by hydrogen peroxide and ascorbate in the presence of dioxygen. Both inactivated forms of the enzyme were investigated. We could highlight the presence of a quinone derivative bound to the protein, assumed as being dopa-quinone, that is absent from active enzyme. Such results suggest that a tyrosinyl radical transiently forms during catalysis. Moreover we could show that addition of substrate tyramine to H2O2 incubates is responsible for a partial protection of DbH against inactivation.

Topics: Animals; Ascorbic Acid; Cattle; Dihydroxyphenylalanine; Dopamine beta-Hydroxylase; Electrophoresis, Polyacrylamide Gel; Hydrogen Peroxide; Oxygen; Spectrophotometry, Ultraviolet; Tyramine; Ultraviolet Rays

2,4,5-Trihydroxyphenylalanine (TOPA) oxidizes in solution to form a quinone derivative that is a non-NMDA glutamatergic agonist and neurotoxin. DOPA can autoxidize in physiological solutions to form small amounts of both TOPA and TOPA quinone. We report here that this conversion can be dramatically enhanced by iron (II) alone, but more so by iron (II) in the presence of hydrogen peroxide. This conversion is of sufficient magnitude that the resulting product can elicit non-NMDA, glutamate receptor-mediated electrical responses in cultured cortical neurons isolated from rat. This finding suggests that TOPA quinone may play a role in pathological processes involving abnormal iron metabolism in catecholaminergic neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Ascorbic Acid; Cells, Cultured; Chromatography, High Pressure Liquid; Dihydroxyphenylalanine; Electrophysiology; Hydrogen Peroxide; Iron; Neurons; Neurotoxins; Oxidation-Reduction; Rats