Creatine—A Dispensable Metabolite?
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Ask any medical student for a definition of the terms creatinine or creatine kinase (CK), and he or she will come up with a precise answer. Ask the same person for a definition of creatine, and the answer will be less precise. In general terms, creatine is regarded as a muscle energizer, and in medical terms creatine is considered as the mother substance for both phosphocreatine (PCr) and creatinine (Figure). But what is creatine? Creatine is a nitrogenous organic acid, derived from glycine, l-arginine and S-adenosyl-l-methionine which is involved in energy transfer in the form of PCr and which is metabolized to creatinine to be excreted by the kidney. The bulk of creatine is stored in muscle, hence creatine’s name, derived from the Greek word for flesh (τό κϱέας). The mammalian body derives about half of its creatine stores from meat sources in food; the other half is made in the kidney and liver (Figure). The first enzyme in the pathway is l-arginine:glycine amidino transferase. The second enzyme in the pathway of creatine synthesis is arginine-glycine aminotransferase.1 Creatine (or β-methyl guanidoacetic acid, a β-amino acid) is nonenzymatically converted to creatinine. Up until now, creatine has been considered essential for muscle energetics and function.
Article, see p 945
Cardiovascular scientists have long regarded creatine as an essential metabolite in the network of energy transfer.2,3 …