Thermostability reinforcement through a combination of thermostability-related mutations of N-carbamyl-D-amino acid amidohydrolase

For the improvement of N-carbamyl-D-amino acid amidohydrolase (DCase), whic h can be used for the industrial production of D-amino acids, the stability of DCase from Agrobacterium sp. KNK712 was improved through various combin ations of thermostability-related mutations. The thermostable temperature ( defined as the temperature on heat treatment for 10 min that caused a decre ase in the DCase activity of 50%) of the enzyme which had three amino acids , H57Y, P203E, and V236A, replaced was increased by about 19 degrees C. The mutant DCase, designated as 455M, was purified and its enzymatic propertie s were studied. The enzyme had highly increased stability against not only temperature but also pH, the optimal temperature of the enzyme being about 75 degrees C. The substrate specificity of the enzyme for various N-carbamy l-D-amino acids was changed little in comparison with that of the native en zyme. Enzymochemical parameters were also measured.