Purification and Characterization of Aspartase from Hafnia alvei

Aspartase (EC 4.3.1.1) from Hafnia alvei was purified to homogeneity by a combination of DEAE-cellulose, Red A-agarose, and Sepharose 6B chromatography. The purified enzyme appeared homogeneous on denatured SDS-polyacrylamide gel electrophoresis. The purified enzyme was a tetrameric protein composed of identical subunits with a molecular weight of 55,000 daltons. The optimum pH for the enzymatic reaction was 8.5 and the optimum temperature for maximum activity was $45^{\circ}C$. The enzyme has an absolute requirement of divalent metal ions ($Mg^{2+}$, $Mn^{2+}$) at the alkaline pH. The enzyme, however, was inactivated in the presence of other divalent cations such as $Zn^{2+}$, $Ca^{2+}$. The helical content of the purified enzyme was estimated by CD spectropolarimetry to be 61%.