חלבון הנשא ADP/ATP

The ADP/ATP carrier is a protein dimer of 30 kilodaltons found abundantly within the inner mitochondrial membrane. It acts as an antiporter that enables the entry of ADP into the mitochondrial matrix and the exit of ATP into the intermembrane space.

The inner membrane also has another transporter, which mediates the simultaneous import of an inorganic phosphate and a proton.

Both of these carrier proteins function with the help of proton-motive forces present across the inner mitochondrial membrane.

The process begins when an ADP from the intermembrane space attaches to the nucleotide-binding site on the ADP/ATP carrier protein. This causes a conformational change in the antiporter, which allows the release of ADP into the mitochondrial matrix.

Similarly, when an inorganic phosphate molecule and a proton binds to the phosphate carrier, the carrier undergoes a conformational change and subsequently transports the phosphate and the proton to the matrix. 

Upon reaching the matrix, the substrate molecules diffuse and bind to the enzymatic pockets of the ATP synthase to be converted into ATP.

Next, the newly synthesized ATP binds to the ADP/ATP carrier, causing a conformational change in the antiporter. This enables ATP to enter the intermembrane space and then exit the mitochondria into the cytosol to be utilized by different cell organelles.