Microbial deracemization of α-amino acids

We screened new microorganisms having deracemization activity of α-amino acids and isolated some active strains. Whole cells of these strains were capable of inverting the chirality of 4-chlorophenylalanine from d- to l-configuration. In particular, Nocardia diaphanozonaria JCM 3208 exhibits the deracemization activity towards wide variety of α-amino acids, such as phenylglycine and 2-aminoheptanoic acid. Examination of the time course of the reaction revealed that α-keto acid was produced as the key intermediate. In addition, mechanistic studies using cell-free extract suggested that deracemization process is realized by two enzymatic reactions; d-stereoselective oxidative deamination reaction and l-selective transamination reaction. Finally, we could establish the reaction conditions utilizing the cell-free system to proceed the deracemization of phenylalanine, which was degraded when the whole cells were used as the biocatalyst.