Incorporation of Na+ - Ca2+ antiporter and of (Na+ + K+)-ATPase into liposomes and demonstration of their non-identity.
(Na+ + K+)-ATPase was isolated from the grey matter of brain and incorporated into liposomes. Most of the reconstituted enzyme was oriented 'inside-out' with respect to its in vivo orientation and externally added ATP promoted Na+ uptake that was inhibitable by internally trapped ouabain. Using the same proteoliposomes, an Na+ - Ca2+ exchange system was observed as indicated by the following pieces of evidence. (1) The Na+ gradient provided the only readily apparent driving force for acceleration of Ca2+ accumulation into proteoliposomes. (2) The antiporter was specific for Ca2+, high Mg2+ excess did not inhibit Ca2+ antiport. (3) The Na+ efflux was dependent on the extravesicular Ca2+ concentration. (4) The Na+ efflux was not inhibited by tetrodotoxin. The demonstrated Na+ - Ca2+ exchange could not be related to (Na+ + K+)-ATPase protein, since it was not purified with (Na+ + K+)-ATPase, as followed from transport studies with liposomes containing (Na+ + K+)-ATPase of different specific activity. The results strongly indicate that plasma membranes isolated from the grey matter of brain contain an Na+ - Ca2+ exchange system and that the proteoliposomes are suitable for further purification of the carrier molecule.
D000818:Animals; D001693:Biological Transport, Active; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D007668:Kidney / Q000201:enzymology; D008081:Liposomes; D008565:Membrane Proteins / Q000378:metabolism*; D010539:Permeability; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
D002352:Carrier Proteins; D008081:Liposomes; D008565:Membrane Proteins; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium