Saturday, December 19, 2009

Creatine Phosphate

Creatine phosphate, or phosphocreatine (PCr), is a phosphorylated creatine molecule that acts as a rapidly mobilizable reserve of high-energy phosphates in skeletal muscle and brain: creatine phosphate can anaerobically donate a phosphate group to ADP to form adenosine triphosphate (ATP) during the first 2 to 7 seconds following an intense muscular or neuronal effort. On the converse, excess ATP can be used during a period of low effort to convert creatine to phosphocreatine. The reversible phosphorylation of creatine is catalyzed by several creatine kinases. The presence of creatine kinase (CK-MB, MB for muscle/brain) in plasma is indicative of tissue damage and is used in the diagnosis of myocardial infarction. The cell's ability to generate phosphocreatine from excess ATP during rest, as well as its use of phosphocreatine for quick regeneration of ATP during intense activity, provides a spatial and temporal buffer of ATP concentration. In other words, creatine phosphate acts as high-energy reserve in a coupled reaction; the energy given off from donating the phosphate group is used to regenerate the other compound - in this case, ATP. Creatine phosphate plays a particularly important role in tissues that have high, fluctuating energy demands such as muscle and brain.

Phosphocreatine is formed from parts of three amino acids: Arginine (Arg), Glycine (Gly), and Methionine (Met). It can be synthesized by formation of guanidinoacetate from Arg and Gly (in kidney) followed by methylation (S-adenosyl methionine, SAM is required) to creatine (in liver), and phosphorylation by creatine kinase (ATP is required) to phosphocreatine (in muscle); catabolism: hydrolysis to creatinine. Phosphocreatine is synthesized in the liver and transported to the muscle cells, via the bloodstream, for storage. Creatine phosphate shuttle help transport of high energy phosphate from mitochondria.