D-Carbamoylase is used in the production of D-amino acid with D-Hydantoinase. After it is cloned in pTRC99A expression vector, it is purified by FPLC for characterization of it. Its optimum reaction temperature is 50℃, and optimum reaction pH is pH 7.5. Its activity is maintained within 50℃, incubated in 30min.. D-Carbamoylase is inhibited its reaction bi-product, ammonium and carbonate ion and some heavy metal ions, $Zn^{2+}, Co^{2+}, Ni^{2+}$. Because Cysteine participates in D-Carbamoylase activity, its activity is recovered by incubation in 1mM DTT. Also, DTT is useful than other anti-oxidants and reducing agents. Because D-hydantoinase, using with D-Carbamoylase for production of D-amino acid, is very thermostable, we made attempt to improve on its thermostability by random mutagensis for higher yield of production and mutant 111-28 is improved on it. Mutant 111-28 is stable in incubation of 55℃ for 30 minute, as if original enzyme has 70% residual activity.
