Abstract: | The functional molecular weight of the plasma membrane Ca2+-ATPase of radish (Raphanus sativus L.) seeds was determined by measuring the Ca2+-dependent ATPase activity and the MgATP-dependent Ca2+ transport activity of membrane samples irradiated, in the lyophilized state, with γ rays from 60Co] source. The results gave a target size of about 270,000 dalton for both the measured activities, thus confirming (i) that both activities are catalyzed by the same enzyme and (ii) the similarity between the plasma membrane Ca2+-ATPase of higher plants and that of the erythrocytes. |