Creatine is a nitrogenous low-molecular-weight water-soluble organic acid mostly stored in muscle. Mammals get creatine from their diet - meat, fish, and supplements contain L-arginine (an essential amino acid), among other amino acids such as glycine and S-adenosyl-L-methionine, which are involved in energy transfer via phosphocreatine. These can be metabolized to creatine before excretion through the kidney. After arginine enters the body, it is absorbed in the intestinal epithelium to the bloodstream and transported to the liver via an amino acid transporter where it undergoes two metabolic reactions. First, arginine is used to form guanidinoacetic acid in a reaction catalysed by glycine amidinotransferase, then that product undergoes a reaction catalysed by guanidinoacetate N-methyltransferase to form creatine. Creatine then exits the hepatocyte and enters the blood via a sodium- and chloride-dependent creatine transporter; here, it can induce systemic oxidative stress and lead to the toxic effect of cell death.

Metabolism and Physiological Effects of Creatine References