I tell my students to remember to look for the suffix - ase. When you see an ase, you know you are dealing with an enzyme.
CK = creatine kinase.
The serum creatine kinase level is elevated in many muscle diseases. This enzyme is released from damaged cardiac or skeletal muscle tissue. Enzymes from the two types of muscle tissue can be differentiated by special lab analysis called electrophoretic analysis. Mature skeletal muscle releases mostly the MM isoenzyme, while mature cardiac muscle will release mostly the MB isoenzyme. Injured muscle will also release many other enzymes.
According to Andrew G. Engel, M. D., Professor of Neuroscience at the Mayo Medical School, "The serum CK level is a sensitive index of muscle fiber injury in a myopathy; it also can increase slightly or modestly in motor neuron disease, in chronic peripheral neuropathies, after severe voluntary exertion, or following a convulsion."
Creatine phosphate (phosphocreatine) is directly involved in energy metabolism with ATP. Phosphocreatine requires the presence of creatine kinase (CK, the enzyme) to accelerate the metabolic conversion process. Phosphocreatine donates its phosphate group to ADP in a reaction catalyzed (accelerated) by CK, thus replenishing ATP. Without CK, the muscle cells wouldn’t have enough energy to contract for very long.
Several things can raise the CK (or CPK* for Phosphocreatine Kinase) level, including sitting or laying down too long in the same position, resulting in muscle compression. For this reason, it is not a good idea to do a CK first thing in the morning. Also, you would expect CK levels to be sky high during and after surgery, especially cardiac or vascular surgery. Any major trauma like this can result in very high CK levels.
If a base-line has been established during non-traumatic status, taking a CK measurement after a presumed periodic paralysis attack can help demonstrate muscle damage. When a neuromuscular disease has advanced to the point where there is significant progressive muscle deterioration, as is the case in advanced forms of Permanent Muscle Weakness (PMW), CK levels can help monitor the progress of deterioration and should also be a useful tool in demonstrating the effectiveness of medications and other therapies in decreasing the rate of muscle deterioration.
The link below is to the article, "Simply Stated . . .The Creatine Kinase Test," from the Muscular Dystrophy Association's Quest Magazine:
*Note: David S. Goldstein, M.D., Ph.D., senior investigator at NIH, and Chief of the Neurochemistry Section at National Institute of Neurological Disorders and Stroke, refers to the same enzyme as CPK.