While mitochondrial creatine kinase is directly involved in formation of phospho-creatine from mitochondrial ATP, cytosolic CK regenerates ATP from ADP, using PCr. The functional entity of the latter two mitochondrial CK isoforms is an octamer consisting of four dimers each. In addition to those three cytosolic CK isoforms, there are two mitochondrial creatine kinase isoenzymes, the ubiquitous and sarcomeric form. The genes for these subunits are located on different chromosomes: B on 14q32 and M on 19q13. There are, therefore, three different isoenzymes: CK-MM, CK-BB and CK-MB. In the cells, the 'cytosolic' CK enzymes consist of two subunits, which can be either B (brain type) or M (muscle type). Ĭlinically, creatine kinase is assayed in blood tests as a marker of damage of CK-rich tissue such as in myocardial infarction (heart attack), rhabdomyolysis (severe muscle breakdown), muscular dystrophy, autoimmune myositides, and acute kidney injury. Thus creatine kinase is an important enzyme in such tissues. In tissues and cells that consume ATP rapidly, especially skeletal muscle, but also brain, photoreceptor cells of the retina, hair cells of the inner ear, spermatozoa and smooth muscle, PCr serves as an energy reservoir for the rapid buffering and regeneration of ATP in situ, as well as for intracellular energy transport by the PCr shuttle or circuit. This CK enzyme reaction is reversible and thus ATP can be generated from PCr and ADP. CK catalyses the conversion of creatine and uses adenosine triphosphate (ATP) to create phosphocreatine (PCr) and adenosine diphosphate (ADP). Ĭreatine kinase ( CK), also known as creatine phosphokinase ( CPK) or phosphocreatine kinase, is an enzyme ( EC 2.7.3.2) expressed by various tissues and cell types. Crystal structure of human brain-type creatine kinase with ADP and creatine.

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