Functional identification of ATP-driven Ca2+ pump in the peribacteroid membrane of broad bean root nodules

A Ca2+ indicator arsenate III was used to demonstrate calcium uptake activi ty of symbiosomes and the peribacteroid membrane (PBM) vesicles isolated fr om broad bean root nodules and placed in the medium containing ATP and Mg2 ions. This process mas shown to be rapidly stopped by vanadate, completely reversed in the presence of the calcium ionophore A23187 but insensitive t o agents abolishing electrical potential or pH difference across the PBM, T he presence of an endogenous calcium pool within isolated symbiosomes and b acteroids was detected using a Ca2+ indicator chlortetracycline, These resu lts prove a primary active transport of Ca2+ through the PBM of legume root nodules and provide the first functional identification of an ATP-driven C a2+-pump, most likely Mg2+-dependent Ca2+-translocating ATPase, in this mem brane. (C) 1999 Federation of European Biochemical Societies.