Question

How does transport of inorganic phosphate from the intermembrane space to the mitochondrial matrix affect the pH difference across the inner mitochondrial membrane?

Answer 1

In mitochondria, many charged small molecules, such as pyruvate, ADP, and Pi, are pumped into the matrix from the cytosol, while others, such as ATP, must be moved in the opposite direction. Carrier proteins that bind these molecules can couple their transport to the energetically favorable flow of H+ into the mitochondrial matrix. Thus, for example, pyruvate and inorganic phosphate (Pi) are co-transported inward with H+ as the H+ moves into the matrix. While ADP is co-transported with ATP in opposite directions by a single carrier protein. Since an ATP molecule has one more negative charge than ADP, each nucleotide exchange results in a total of one negative charge being moved out of the mitochondrion. This ADP-ATP co-transport is thereby driven by the voltage difference across the membrane