FUNCTIONAL ORGANIZATION OF PARTIAL REACTIONS OF NA+ + K+ - ACTIVATED ATPASE WITHIN RED CELL MEMBRANE

Effects of false substrates and modifiers of the partial reactions of the Na+, K+-ATPase complex on Na+ transport in resealed red cell ghosts were studied. A ouabain-sensitive efflux of Na+ into a Na+-free medium was initiated when p-nitrophenylphosphate (NPP) and K+ were added to the medium. Na+-efflux into a Na+-containing medium required the simultaneous presence of K+, NPP, and a nucleotide in the medium. When Na+-efflux was stimulated, NPP hydrolysis was increased. We conclude that the K+-dependent phosphatase facing the medium-side of the membrane is the primary ion translocator, and that an enzyme on the matrix-side of the membrane supplies a physiological substrate (the phosphorylated intermediate") for the translocator-phosphatase. © 1969."