Industrial biotransformations for the production of d-amino acids

Optically pure d-amino acids are industrially manufactured by biotransformations of cheap starting materials produced by chemical synthesis or fermentation in combination with the development of enzyme catalysts suitable for the starting materials. dl-Alaninamide, an intermediate of the chemical synthesis of dl-alanine, was efficiently converted to d-alanine by stereoselective hydrolysis with a d-isomer specific amidohydrolase produced by Arthrobacter sp. NJ-26. The total utilization system of dl-alaninamide for the production of optically pure d- and l-alanine was constructed by stereospecific amidohydrolases. On the other hand, d-amino acids were also produced from corresponding l-isomers, which are efficiently manufactured by fermentation. d-Glutamic acid was produced from l-glutamic acid. l-Glutamate was converted to the dl-form by the recombinant glutamate racemase of Lactobacillus brevis ATCC8287. Then l-glutamate in a racemic mixture was selectively decarboxylated to γ-aminobutyrate by the l-glutamate decarboxylase of E. coli ATCC11246. As a result of successive enzymatic reactions, d-glutamate was efficiently produced from l-glutamate by a one-pot reaction. d-Proline was produced by the same strategy from l-proline using the recombinant proline racemase of Clostridium sticklandii ATCC12262. In this case, l-proline was degraded by Candida sp. PRD-234. The strategy from l-amino acids to d-amino acids could be applicable to the manufacture of many d-amino acids.