The Reactions of Sodium and Potassium Ion-activated Adenosine Triphosphatase with Specific Antibodies: IMPLICATIONS FOR THE MECHANISM OF ACTIVE TRANSPORT

Abstract

Abstract Native sodium and potassium ion-activated adenosine triphosphatase ((Na+ + K+)-ATPase) and the larger polypeptide chain of this enzyme have been used as antigens to obtain specific antibodies. It is demonstrated that these antibodies bind to the native enzyme only at sites on one or the other of the two polypeptide subunits. The locations of the antigen-antibody complexes were determined with the electron microscope using ferritin conjugated γ-globulins. These experiments demonstrate that the antigenic sites on the large subunit, recognized by the anti-large chain antibody, are located only on the inner surface of the plasma membrane in the intact cell. The γ-globulins studied in these experiments do not inhibit (Na+ + K+)-ATPase when they are bound to the enzyme at saturating concentrations. These results rule out any mechanisms for this enzyme which require large movements of the protein through the plane of the bilayer, and therefore rule out any diffusional carrier mechanism for the active transport of alkali metal ions.