How does the Na + pump undergo a series of conformational changes as it exchanges Na + ions for K + ?
A.
The binding of cytosolic Na + (1) and the subsequent phosphorylation by ATP of the cytosolic face of the pump (2) induce the protein to undergo conformational changes that transfer the Na + across the membrane and release it outside the cell (3).
B.
The high-energy linkage of the phosphate to the protein provides the energy to drive the conformational changes.
C.
The binding of K + from the extracellular space (4) and the subsequent dephosphorylation (5) allow the protein to return to its original conformation, which transfers the K + across the membrane and releases it into the cytosol (6).
D.
The real pump in mammalian cells contains three binding sites for Na + and two for K + . The net result of one cycle of the pump is therefore the transport of three Na + out and two K + in. Ouabain inhibits the pump by preventing K + binding (4).