Creatine kinase

Creatine kinase is an enzyme that reversibly transfers a phosphate group between phosphocreatine and ADP, producing creatine and ATP or the reverse.

Phosphocreatine: Phosphocreatine is a phosphorylated form of creatine that stores and donates a phosphate group. It supplies the phosphate that creatine kinase transfers to ADP.
Creatine kinase test: A creatine kinase test measures the enzyme’s activity in a blood sample. Elevated blood activity can signal enzyme release from damaged tissue.
Phosphagen kinase: Phosphagen kinases are enzymes that transfer phosphate between ATP and small-molecule phosphagens. Creatine kinase belongs to this enzyme family, which supports rapid energy buffering.
Phosphocreatine shuttle: The phosphocreatine shuttle moves high-energy phosphate equivalents from mitochondria to sites of ATP use. Creatine kinase catalyzes the phosphate exchange that enables this intracellular energy transfer.
Cardiac troponin: Cardiac troponin is a heart-muscle protein measured in blood to detect myocardial injury. Troponin is more specific and sensitive than creatine kinase-MB for diagnosing myocardial infarction.
Adenosine triphosphate: Adenosine triphosphate is a nucleotide that cells use as a principal source of chemical energy. Creatine kinase regenerates ATP from ADP during periods of high energy demand.
Creatine kinase-MB: Creatine kinase-MB is an isoenzyme found mainly in cardiac muscle, with smaller amounts in other tissues. Its blood concentration has been used to assess heart-muscle injury.
Kinase: A kinase is an enzyme that transfers a phosphate group to a substrate. Creatine kinase is a specialized kinase whose reaction is reversible.
Muscle contraction: Muscle contraction is the generation of force by muscle fibers through interactions between actin and myosin. Creatine kinase helps replenish ATP consumed during rapid cycles of contraction.
Lactate dehydrogenase: Lactate dehydrogenase is an enzyme that interconverts lactate and pyruvate while transferring electrons. Like creatine kinase, it can enter blood after tissue injury, but it catalyzes a different reaction.

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