Creatine phosphokinase (CPK), also known as creatine kinase (CK), is an enzyme preparation isolated from rabbit muscle. This specialty biochemical reagent is used in laboratory research and diagnostic assays to investigate muscle metabolism, phosphate transfer reactions, and enzymatic activities. It catalyzes the reversible conversion of creatine and ATP to phosphocreatine and ADP. With a specific activity of >30 U/mg protein, it appears as a white to off-white powder. In clinical diagnostics, CPK reagents like this are employed in enzymatic assays to measure CK levels in blood samples, helping detect myocardial infarction, muscle damage, rhabdomyolysis, muscular dystrophy, and other conditions. It also supports research on exercise physiology and muscle health.