Diversity and versatility of microbial hydantoin-transforming enzymes

Microbial hydantoin transformation has been applied to produce optically active amino acids through ring-opening hydrolysis of cyclic ureides and successive hydrolytic reactions of N-carbamoyl amino acids.

Abstract

Microbial hydantoin transformation has been applied to produce optically active amino acids. The transformation involves ring-opening hydrolysis of cyclic ureides and successive hydrolysis of N-carbamoyl amino acids. The enzymes catalyzing these two hydrolytic reactions were purified from various microorganisms and characterized. In the N-carbamoyl amino acid hydrolysis, three enzymes, N-carbamoyl-d-amino acid amidohydrolase, N-carbamoyl-l-amino acid amidohydrolase and β-ureidopropionase, are involved. The former two enzymes only hydrolyze N-carbamoyl-α-amino acids d- or l-stereospecifically, respectively. The last one acts upon N-carbamoyl-α-, -β- and -γ-amino acids, and shows l-stereo-specificity to N-carbamoyl-α-amino acids. A variety of enzymes are also involved in cyclic ureide hydrolysis. d-Hydantoinase hydrolyzes 5-monosubstituted hydantoins d-stereospecifically and preferably hydrolyzes dihydropyrimidines. Imidase, which acts well upon cyclic imides, also hydrolyzes dihydropyrimidines. N-Methylhydantoin amidohydrolase hydrolyzes 5-monosubstituted hydantoins l-stereospecifically with concomitant hydrolysis of ATP to ADP. Dihydroorotase hydrolyzes six-membered cyclic ureide, dihydroorotate, l-stereospecifically. The strict stereospecificities of these hydantoin-transforming enzymes contribute to produce optically active compounds.