A set of related enzymes most abundant in the heart, brain, skeletal muscle and other tissues with high energy requirements. CK is critical in maintaining a constant concentration of ATP under conditions of high expenditure of ATP energy, and is ordinarily contained entirely within the muscle. If the heart or other muscle is damaged, CK will be released into the blood. Blood levels of CK, formerly used as a heart attack indicator, have been replaced by levels of troponin.
