Minimization of by-product formation during d-amino acid oxidase catalyzed racemate resolution of d/l-amino acids

d-Amino acid oxidase (DAAO, EC 1.4.3.3) was applied to biotransformations of d-methionine or d-phenylalanine to the corresponding α-keto acids starting with the racemic mixtures as substrates. Hydrogen peroxide is formed as by-product in the DAAO-catalyzed reaction. This reactive species is disadvantageous for the racemate resolution process due to the chemical decarboxylation of the α-keto acids as well as the inactivation of the DAAO. To immediately remove the generated H2O2 during the biotransformations three different commercially available catalases (bovine liver, Aspergillus niger or Micrococcus lysodeikticus) were tested. By external addition of catalase from Micrococcus lysodeikticus an α-keto acid yield of 100% was obtained after complete conversion of the d-phenylalanine. The space-time yield of the α-keto acid production increased up to 8.26 g l−1 h−1 compared to the process without addition of catalase (0.14 g l−1 h−1). Another observation was a relationship between Δ-redoxpotential and H2O2 concentration which should be the basis for an automated catalase feeding in the amino acid resolution process using DAAO in the future.