The process by which protons and anions enter the cell from outside the cell through co-localization is called the proton-anion cotransport theory. This theory is based on the chemi-osmotic model of Peter Mitchell (1968).
According to this theory a specific ion is transported by a specific carrier. Cell membranes contain ATP. ATP-ase enzymes break down ATP to generate energy. Under the influence of this force, protons (H+) come from the inner surface of the cell to the outer surface of the cell. This phenomenon is called proton pump. This increases the pH on the inside of the cell and decreases the pH on the outside. This phenomenon is called pH gradient. For the same reason the ‘+’ charge on the inside of the cell decreases and the ‘+’ charge on the outside increases. This phenomenon is called Protential gradient. The pH gradient and proton gradient together are called Proton Motive Force (PMF). When the Proton Motive Force is generated, the inactive proteins on the outer surface of the cell are converted into active proteins. Active proteins act as carriers and transport cations (K+) from the cell surface to the cell surface. This increases the amount of cations in the cell’s interior. Because of this, protons (H+) from the outer layer of the cell want to enter the inner layer of the cell. Then protons and anions co-exist from the outer surface of the cell to the inner surface of the cell. Anions and cations then combine to meet the cell’s mineral salt needs.
