THERMOSTABLE N-CARBAMOYL-D-AMINO ACID AMIDOHYDROLASE - SCREENING, PURIFICATION AND CHARACTERIZATION

A thermostable N-carbamoyl-D-amino acid amidohydrolase was found in th e cells of newly isolated bacterium, Blastobacter sp. A17p-4. The bact erium also showed D-specific hydantoinase activity. The N-carbamoyl-D- amino acid amidohydrolase activity of the cells exhibited a temperatur e optimum at 50-55 degrees C, and was stable up to 50 degrees C. The N -carbamoyl-D-amino acid amidohydrolase of Blastobacter sp. A17p-4 was purified to homogeneity and characterized. It has a relative molecular weight of about 120000 and consists of three identical subunits with a relative molecular weight of about 40000. N-Carbamoyl-D-amino acids having hydrophobic groups served as good substrates for the enzyme. It has been suggested that D-amino acid production from DL-5-substituted hydantoin involves the action of a series of enzymes involved in pyri midine degradation, namely amide-ring opening enzyme, dihydropyrimidin ase, and N-carbamoylamide hydrolyzing enzyme, beta-ureidopropionase. H owever, the purified enzyme did not hydrolyze beta-ureidopropionate; s uggesting that the N-carbamoyl-D-amino acid amidohydrolase coexisting with D-specific hydantoinase, probably dihydropyrimidinase, in Blastob acter sp. A17p-4 is different from beta-ureidopropionase.