Cyclic ureide and imide metabolism in microorganisms producing a d-hydantoinase useful for d-amino acid production

The microbial transformation of dl-5-monosubstituted hydantoins has been applied to industrial scale production of optically active amino acids. Hydantoinase and N-carbamoyl amino acid amidohydrolase, which are the key enzymes in this transformation, from various microorganisms have been studied extensively. Blastobacter sp. A17p-4, which was isolated for d-amino acid production through hydantoin transformation, shows not only diverse cyclic ureide-metabolizing activities including those of d-hydantoinase and N-carbamoyl-d-amino acid amidohydrolase, but also cyclic imide-metabolizing activities. A recent study revealed the participation of d-hydantoinase in the metabolism of cyclic imides and the existence of novel enzymes, imidase and half-amidase, in this bacterium. d-hydantoinase functions in the metabolism of bulky cyclic imides, while imidase functions in that of simple cyclic imides in combination with half-amidase, which functions in the hydrolysis of the imidase reaction products, half-amides. Imidase and half-amidase are different from reported cyclic-amide-metabolizing enzymes, and are widely found in bacteria, yeasts and molds.