This is the second membrane system functioning in oxidative phosphorylation. It promotes transport of  along with that of H⁺ from the cytosol into the matrix compartments as the entrance of the inorganic phosphate is coupled to the entrance of H⁺. This system is aptly designated as Pi-H⁺ symporter. The phosphate translocase system is specific for phosphate.

Thus, the combined action of phosphate and ADP-ATP translocase allows external phosphate and ADP to enter the matrix and the resulting ATP to return to the cytosol, where most of the ATP-requiring cell activities take place. An antiporter exchanges ADP³ and ATP⁴⁻ and is driven by electrical potential across the membrane, where a symporter carries a proton and monobasic Pi and is driven by the proton concentration gradient.