Description
Creatine kinase (CK) catalyzes the reversible phosphorylation of creatine by ATP to form phosphocreatine and ADP. CK consists of two subunits: M (muscle)- and B (brain)-subunits, and has three isoenzymes: CK-MM (found in skeletal muscle), CK-MB (found in cardiac muscle), and CK-BB (found in brain and lung). Clinically, CK levels in blood are used to test for the diagnosis and/or monitoring of myocardial infraction (heart attack), rhabdomyolysis (severe muscle breakdown), muscular dystrophy, and acute renal failure, as elevated CK activity levels are common to such diseases. In this colorimetric assay, CK converts phosphocreatine and ADP to creatine and ATP, where ATP is then used for subsequent enzyme-coupled reactions to form NADPH. CK activity is determined by assaying the rate of NADPH formation, which is proportional to the reduction in absorbance at 340nm over time (ΔOD340nm/min)