Distribution and Properties of a Potassium-dependent Asparaginase Isolated from Developing Seeds of Pisum sativum and Other Plants

Abstract

Asparaginase (EC 3.5.1.1) was isolated from the developing seed of P. sativum. The enzyme depends on the presence of K+ for activity, although Na+ and Rb+ may substitute to a lesser extent. Maximum activity was obtained at K+ concentrations above 20 mM. K ions protected the enzyme against heat denaturation. The enzyme has a MW of 68,300. Asparaginase activity developed initially in the testa, with maximum activity (3.6 .mu.M/h per seed) being present 13 days after flowering. Maximum activity (1.2 .mu.M/h per seed) did not develop in the cotyledon until 21 days after flowering. Glutamine synthetase and glutamate dehydrogenase were also present in the testae and cotyledons but maximum activity developed later than that of asparaginase. K-dependent asparaginase activity was also detected in the developing seeds of Vicia faba, Phaseolus multiflorus, Zea mays, Hordeum vulgare and 2 Lupinus varieties. No stimulation of activity was detected with the enzyme isolated from Lupinus polyphyllus, which has previously been shown to contain a K+-independent enzyme.