The mitochondrial creatine kinase, also known as phosphocreatine kinase (CPK), facilitates energy transport with creatine and phosphocreatine as diffusible intermediates.
Reference: Saks 2000 Acta Physiol Scand
MitoPedia topics: Enzyme
The mitochondrial CK, which is bound to the outer surface of the inner mitochondrial membrane, hydrolyses ATP to ADP, which is directly transported to the adenine nucleotide translocase (ANT) for regulation of respiration and no release of ATP occurs. Instead, the mitochondrial CK phosphorylates Cr to PCr which is transported into myofibrils where PCr is dephosphorylated to Cr by the myofibrillar CK. The phosphoryl group from PCr is then used to rephosphorylate ADP into ATP while Cr diffuses back to the mitochondria to be rephosphorylated to PCr.
The ADP produced in the intermembrane space by the mitochondrial CK stimulates respiration more effectively than ADP produced directly in the cytoplasm. This means that Cr, by activating the mitochondrial CK reaction can directly control the mitochondrial energy production.