Creatine Kinase, also known as CK, CPK, Creatine Kinase, Creatine Phosphokinase is an enzyme present in muscle, brain, and other tissues of vertebrates that catalyzes the reversible conversion of ADP and phosphocreatine into ATP and creatine. Clinical Significance: Detection of Heart Disease, Liver Disease, Diseases of the Central Nervous System and Thyroid Disease. Creatine Kinase CPK products are extensively used in multi-analyte clinical chemistry controls and calibrators for major IVD manufacturers. MW: 85 kDa (dimer).