Creatine kinase, also known as creatine phosphokinase, is an enzyme found mainly in the heart, brain and skeletal muscle. Creatine kinase catalyzes the conversion of creatine and makes use of adenosine triphosphate to create phosphocreatine and adenosine diphosphate.
In tissues and cells that consume adenosine triphosphate (ATP) rapidly, especially skeletal muscle, phosphocreatine acts as an energy reservoir for the rapid regeneration and buffering of the ATP. This alone makes creatine kinase an extremely important enzyme in these types of tissues.
In cells, creatine kinase enzymes consist of two subunits, either brain (B) type or muscle (M) type. This makes for three different types of isoenzymes, namely CK-MM, CK-BB and CK-MB. The genes for these subunits are located on the chromosomes 14q32, which houses the brain type, and 19q13, which houses the muscle type.
Creatine kinase is determined routinely in a medical laboratory. While it used to be determined specifically in cases of patients with chest pains, that test has now been replaced by troponin. At rest, normal values of creatine kinase are usually between 60 and 174 IU/L. In both healthy and diseased individuals, levels of creatine kinase may be high. Exercise increases the outflow of it into the blood stream for up to a week and is the number one cause of high amounts of it in the blood.