Abstract
Asparaginase (EC 3.5.1.1) activity was determined in non-germinating and germinating seeds of five Egyptian cowpea (Vigna unguiculata) cultivars (Kareem 7, Dokki 331, Kafer El-Sheikh 1, Kaha 1, and Fodder). In all cultivars, asparaginase specific activity was higher in germinating seeds. The highest specific activity of asparaginase was observed in Fodder cultivar. Asparaginase was purified from Fodder cultivar germinating seeds and resolved, by DEAE sepharose, into three forms named ASPG I, ASPG II, and ASPG III. The molecular mass of ASPG II was 70 kDa for native enzyme using gel filtration and similar to 35 kDa after SDS-PAGE electrophoresis. This indicates a dimeric structure for ASPG II. ASPG II had a Km value of 1.25 mM for asparagines, a pH optimum at 8.0 and temperature optimum and heat stability at 40 degrees C. The Fodder cultivar ASPG II was specific for L-asparagine, did not hydrolyze D-asparagine and was not specific for L-glutamine. Ni2+ and Co2+ may act as activators on ASPG II but Hg2+, Ba2+, Zn2+ and Mn2+ had inhibitory effect. The purified asparaginase may be valuable in chemotherapeutic treatments.