TY - CHAP M1 - Book, Section TI - Disorders of Creatine and Ornithine Metabolism A1 - Stockler-Ipsiroglu, Sylvia A2 - Kline, Mark W. PY - 2018 T2 - Rudolph's Pediatrics, 23e AB - Creatine is both ingested in the diet and synthesized mainly in the liver and pancreas by the action of arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT), with arginine, glycine, and S-adenosyl methionine as essential substrates (Fig. 138-1). AGAT catalyzes the first of the two reactions involved in the de novo synthesis of creatine. This reaction uses arginine and glycine as substrates and yields guanidinoacetate and ornithine as products. Guanidinoacetate is further converted to creatine by the action of GAMT, using S-adenosylmethionine as a methyl group donor, with this reaction consuming a significant fraction of all methyl groups. Creatine reaches muscle and brain via an active transmembrane creatine transport system (CRTR). Creatine is then used in the cellular pool of creatine/creatine-phosphate, which together with creatine kinase and adenosine triphosphate (ATP)/adenosine diphosphate (ADP) provides a high-energy phosphate buffering system. Intracellular creatine and creatine phosphate are nonenzymatically converted to creatinine, with a daily turnover rate of 1.5%. Creatinine is excreted in urine, and the daily urinary creatinine excretion is directly proportional to total body creatine. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/03/28 UR - accesspediatrics.mhmedical.com/content.aspx?aid=1182928654 ER -