The sodium pump is the major ion transport ATPase of animal cell plasma membranes which energizes many vital homeostatic transport activities in cells and organs. The first objective of the proposed research is to analyze movements of the sodium pump on the cell surface. Through the use of synthetic peptides and purified proteins, new antibodies will be made that react with the beta subunit of the human enzyme. Such antibodies should bind to the enzyme on the outside of human cells and permit quantitation of the number of sodium pump molecules on the cell surface. These antibodies will also be used to study the folding pattern of the beta subunit, and to study the traffic of the pump to and from the surface of the cell. The second objective is to understand how cells previously selected for overproduction of the sodium pump inhibit the excess enzyme activity. Assays of subcellular fractions will attempt to localize a pool of inhibited enzyme in the overproducing cells. Antibodies to enzyme subunits will be used to detect alterations in subunit production or recognize protein modifications. The combination of activity and antibody analyses is expected to define a site inside the cells where biochemical regulatory events turn off sodium pumps. The sodium pump is the major ion transport enzyme of animal cell plasma membranes. It maintains a low concentration of sodium inside the cell compared to outside, and this difference between the sodium outside and inside provides the energy for many vital homeostatic transport activities in cells and organs. The ability of cells to control the sodium pump activity could be important for conserving cellular energy, controlling other membrane transport activities, and responding to ionic stresses. This research should contribute to our understanding of the control of cellular sodium pump activity.
