Kinetic Modeling of Amino Acid Oxidation Catalyzed by a New D-Amino Acid Oxidase from Arthrobacter protophormiae

摘要

Amino acid oxidases, which enantiospecifically catalyze the oxidative deamination of either D- or L-amino acids, belong to the class of oxidoreductases functioning with a tightly bound cofactor. This cofactor favors industrial applications of Z)-amino acid oxidases (D-AAO). Hence, the enzyme is very important for the industrial application in the purification and determination of certain amino acids. In developing the enzyme-catalyzed reaction for large-scale production, modeling of the reaction kinetics plays an important role. Therefore, the subject of this study was the kinetics of the oxidative deamination, a very complex reaction system, which is catalyzed by D-AAO from Arthrobacter protophormiae using its natural substrate D-methionine and the aromatic amino acid 3,4-dihydroxyphenyl-D-alanine (D-DOPA). The kinetic parameters determined by the measurement of the initial rate and nonlinear regression were verified in batch reactor experiments by comparing calculated and experimental concentration-time curves. It was found that the enzyme is highly specific towards D-methionine (K{sub}m = 0.24 mM) and not as specific to D-DOPA as a substrate (K{sub}m - 9.33 mM). The enzyme activity towards D-methionine ((V{sub}m){sup}(D-Met) = 3.01 U/mL) was approx. seven times higher than towards D-DOPA ((V{sub}m){sup}(D-DOPA)= 20.01 U/mL). The enzyme exhibited no activity towards L-methionine and L-DOPA. Batch and repetitive batch experiments were performed with both substrates in the presence and in the absence of catalase for hydrogen peroxide decomposition. Their comparison made it possible to conclude that hydrogen peroxide has no negative influence on the enzyme activity.