PURIFICATION AND CHARACTERIZATION OF VIGNA UNGUICULA TA CULTIVER ASPARAGINASE

Asparaginase (EC 3.5.1.1) activity was determined in non germinating seeds and germinating seeds of five Egyptian cowpea (Vigna unguiculata) cultivars (Kareem 7, Dokki 331, Kafer El-Sheikh 1, Kaha 1 and Fodder). The specific activities of germinating seeds asparaginase in different cultivars were higher than the specific activities of non germinated seeds of these cultivars. Asparaginase was purified from Fodder cultivar germinating seeds (the highest specific activity) and resolved into three peaks with asparaginase activities by DEAE sepharose, designated by asp I, asp II and asp III. The molecular weight of asp II was 70 kDa for native enzyme using gel filtration. By using SDS-PAGE electrophoresis, asp II had molecular weight about 35 kDa suggesting that a dimeric structure for asp II. AspII had a Km value 1.25 mM for asparagine and a pH optimum at 8.0. Asp II had a temperature optimum and heat stability at 40 °C. The fodder cultivar asp II activity was specific for L-asparagine and did not hydrolyze D-asparagine. It is not specific for L-glutamine. Ni2+ and Co2+ had activator effects on asp II but other metals ions had inhibitory effect.