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|Section2= |Section5= |Section6= |Section7= |Section8= }} Creatine ( or 〔(Entry "creatine" ) in ''(Merriam-Webster Online Dictionary )''.〕〔Wells, J. C. (2000). ''Longman Pronunciation Dictionary''. Harlow, England: Pearson Education Ltd.〕) is a nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to all cells in the body, primarily muscle. This is achieved by increasing the formation of adenosine triphosphate (ATP). Creatine was identified in 1832 when Michel Eugène Chevreul isolated it from the basified water-extract of skeletal muscle. He later named the crystallized precipitate after the Greek word for meat, κρέας (''kreas''). Early analysis showed that human blood is approximately 1% creatine, and the highest concentrations are found in animal blood, brain (0.14%), muscle (0.50%), and testes (0.18%). The liver and kidney contain approximately 0.01% creatine. Today, creatine content (as a percentage of crude protein) can be used as an indicator of meat quality.〔http://pubs.acs.org/doi/abs/10.1021/jf60128a026?journalCode=jafcau〕 In solution, creatine is in equilibrium with creatinine. Creatine is a derivative of the guanidinium cation. ==Biosynthesis== Creatine is not an essential nutrient as it is naturally produced in the human body from the amino acids glycine and arginine. In the first step of the biosynthesis these two amino acids are combined by the enzyme arginine:glycine amidinotransferase (AGAT, (EC:2.1.4.1 )) to form guanidinoacetate, this is then methylated by guanidinoacetate N-methyltransferase (GAMT,(EC:2.1.1.2 )), using S-adenosyl methionine as the methyl donor. Creatine itself can be phosphorylated by creatine kinase to form phosphocreatine, which is used as an energy reserve in skeletal muscles and the brain. Synthesis primarily takes place in the kidney and liver, with creatine then being transported to the muscles via the blood. Approximately 95% of the human body's total creatine is located in skeletal muscle. In humans and animals, approximately half of stored creatine originates from food (about 1 g/day, mainly from meat).〔 A study involving 18 vegetarians and 24 non-vegetarians on the effect of creatine in vegetarians showed that total creatine was significantly lower than in non-vegetarians. Since vegetables are not the primary source of creatine, vegetarians can be expected to show lower levels of directly derived muscle creatine. However, the subjects happened to show the same levels after using supplements. Given the fact that creatine can be synthesized from the above-mentioned amino acids, protein sources rich in these amino acids can be expected to provide adequate capability of native biosynthesis in the human body.〔 Genetic deficiencies in the creatine biosynthetic pathway lead to various severe neurological defects. Clinically, there are three distinct disorders of creatine metabolism. Deficiencies of the two synthetic enzymes can cause L-arginine:glycine amidinotransferase deficiency and guanidinoacetate methyltransferase deficiency. Both biosynthetic defects are inherited in an autosomal recessive manner. A third defect, creatine transporter defect is caused by mutations in ''SLC6A8'' and inherited in a X-linked manner. This condition is related to the transport of creatine into the brain. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「creatine」の詳細全文を読む スポンサード リンク
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