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

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. (c) 2007 Elsevier B.V. All rights reserved.