Purification and some properties of α-amylase from post-harvest Pachyrhizus erosus L. tuber

α-Amylase, a starch splitting enzyme, was purified to homogeneity from post-harvest Pachyrhizus erosus L. tuber by successive chromatography on DEAE- and CM-cellulose columns. Purification achieved was 110 fold from the crude extract with a yield of 22.8%. SDS-PAGE showed a molecular weight of 40 kDa for the enzyme. The enzyme is of α-type as it lost total activity in the presence of EDTA, a chelating agent. It is a glycoprotein that contains 2.6% sugar as estimated by the phenol-sulfuric acid method. The enzyme displayed optimum activity at pH 7.3 and 37 °C with an apparent Km value of 0.29% for starch as substrate. The enzyme was strongly inhibited by Cu2+, Fe2+ and Zn2+, moderately by Li2+, Hg+ and Cd2+ and slightly by Ag+, Mg2+ and K+. Calcium ion almost doubled the activity whereas Fe3+, Mn2+ and Na+ enhanced it appreciably.