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.
Chimie, Biologie et Radicaux libres, UMR-CNRS 6517, Faculté des Sciences et Techniques de St-Jérome, case 432, Av. Escadrille Normandie-Niémen, 13397 Cedex 20, Marseille, France.
