Coenzyme regeneration catalyzed by NADH oxidase from Lactobacillus brevis in the reaction of l-amino acid oxidation

Abstract

In this paper l-methionine oxidation catalyzed by l-phenylalanine dehydrogenase from Rhodococcus sp. M4 was studied. It was found that the reaction equilibrium is shifted to the side of reduction, and it was therefore necessary to regenerate NAD + to increase l-methionine conversion. NADH oxidase from Lactobacillus brevis was used for that purpose. The enzyme was kinetically characterized. It was found that the enzyme is inhibited by NAD +. Hence, NADH oxidation catalyzed by NADH oxidase was described by the Michaelis–Menten equation which included anticompetitive NAD + inhibition. l-Methionine oxidation was described by formal double-substrate Michaelis–Menten model which included competitive product inhibition by NADH. 2-Oxo-4-methylthiobutyric acid reduction was described by formal three-substrate Michaelis–Menten kinetics which included competitive inhibition by NAD +. Experiments were carried out in the batch and in the continuously operated enzyme membrane reactor. 100% l-methionine conversion was achieved in the batch reactor. The conversion was lower in the continuously operated enzyme membrane reactor where enzyme deactivation occurred.