mitochondrial inner membrane,
mitochondrial intermembrane space,
In humans, creatine is synthesized primarily in the liver and kidney, from glycine, arginine, and S-adenosylmethionine, in a sequence of two reactions. From the liver, creatine is exported to tissues such as skeletal muscle and brain, where it undergoes phosphorylation and serves as a short-term energy store. The mechanism by which creatine leaves producer tissues is unclear, but its uptake by consumer tissues is mediated by the SLC6A8
Once formed, phosphocreatine undergoes a slow spontaneous reaction to form creatinine, which is excreted from the body.