In the figure below is depicted a membrane and an integral membrane protein called a Na+-K+ ATPase.
In the figure are two triangles that indicate concentration gradients of Na+ and K+ across the membrane.
The Na+-K+ ATPase will transport Na+ ions against its concentration gradient and K+ ions against its concentration gradient.
The series of steps depicted below are as follows:
The figure below represents a sequence of events that occur with the same protein over a period of time
3 Na+ ions bind to the ATPase under conditons of low Na+ concentrations because ATP andthe transport protein has a high affinity for Na+. This means the protein will bind Na+ ions even when the Na+ concentration is low Mg++ bind to the protein . These are exergonic reactions
The transport protein cleaves ATP into ADP and Phosphate ion.The phosphate ion becomes covalently bonded to the protein.The phosphorylation of the protein causes it to become energetically unstable and the protein changes conformation.The shift in conformation of the protein in some manner causes the Na+ to travel across the protein and they are released from the protein on the other side of the membrane because the protein now has a low affinity for Na+ .These are exergonic processes
K+ ions bind to the protein even it there is a low K+ concentration because in this conformation the protein has a high affinity for K+ ions.The covalently bound phosphate group is cleaved from the protein which causes the protein to undergo another conformational shift.
This conformational shift causes the K+ to be in some manner transported across the protein and released on the other side of the membrane. The K+ ion is released because now the protein has a low affinity for K+ ions. The protein is restored to the ordinal conformation of the protein and the process starts again .