Oxidation by hydrogen peroxide of D-amino acid oxidase from Rhodotorula gracilis

D-amino acid oxidase (DAAO) from Rhodotorula gracilis is a flavoenzyme that catalyzes the oxidative deamination of D-amino acid to give the corresponding alpha-keto acids, hydrogen peroxide and ammonia. This enzyme exhibits interesting properties that enable its use in industrial production of semisynthetic cephalosporins. Hydrogen peroxide induced enzyme deterioration that was more remarkable in the case of the apoenzyme when compared with the native holoenzyme. The inactivation rate constant was 3.12x10(-2)mM(-1)min(-1) for the apoenzyme and 6.96x10(-5)mM(-1)min(-1) for the holoenzyme. Fluorescence emission studies have shown the oxidation of tryptophan residues, by H2O2 as responsible of enzyme inactivation. The oxidized tryptophans did not seem to be involved in the coenzyme FAD binding to DAAO apoprotein.