PROPERTIES OF ATPASES OF THE PERIBACTEROID MEMBRANE IN ROOT-NODULES OF YELLOW LUPINE

Peribacteroid membrane (PBM) vesicles isolated from root nodules of yellow lupine exhibit Mg2+-dependent H+-ATPase activity with a pH optimum of 5.4-5.7, as was demonstrated spectrophotometrically using the pH probe acridine orange. Proton transport and ATP hydrolysis were simultaneously inhibited by orthovanadate and nitrate at optimal pH values, which suggests the presence of two H+-ATPases -of the plasmalemma and the tonoplast types-on the PBM. In addition to this, activity of Mg2+,Ca2+-ATPase with broad substrate specificity and a pH optimum of 6.2-6.4 was clarified on PBM vesicles. The Mg2+-dependent ATPase activity was more sensitive to molybdate, nitrate, and vanadate, whereas Ca2+-dependent activity was more sensitive to fluoride and Cu2+ ions. The rate of CaATP2- was 1.5 times higher than that of MgATp2- hydrolysis, the apparent K(m) constituting 0.12 and 0.22 mM, respectively. The obtained data are discussed in the light of current ideas about heterogeneity of ATPases and genesis of the PBM.