ARGINASE FROM KIWIFRUIT - PROPERTIES AND SEASONAL-VARIATION

The in vitro activity of arginase (EC 3.5.3.1) was investigated in you ngest-mature leaves and roots (1-3 mm diameter) of kiwifruit vines (Ac tinidia deliciosa var. deliciosa) during an annual growth cycle, and e nzyme from root material partially purified. No seasonal trend in the specific activity of arginase was observed in roots. Measurements in l eaves, however, rose gradually during early growth and plateaued c. 17 weeks after budbreak. Changes in arginase activity were not correlate d with changes in the concentration of arginine (substrate) or glutami ne (likely end-product of arginine catabolism) in either tissue during the growth cycle. Purification was by (NH4)(2)SO4 precipitation and D EAE-cellulose chromatography. The kinetic properties of the enzyme, pu rified 60-fold over that in crude extracts, indicated a pH optimum of 8.8, and a K-m (L-arginine) of 7.85 mM. Partially-purified enzyme was deactivated by dialysis against EDTA, and reactivated in the presence of Mn2+, Co2+, and Ni2+.