FIGURE 12-35 The phosphate and ATP/ADP transport system in the inner mitochondrial membrane. The coordinated action of two antiporters (purple and green), which results in the uptake of one ADP³⁻ and one HPO₄²⁻ in exchange for one ATP⁴⁻ and one hydroxyl, is powered by the outward translocation of one proton (mediated by the proteins of the electron-transport chain, blue) during electron transport. The outer membrane is not shown here because it is permeable to molecules smaller than 5000 Da.