[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Creatine, phosphocreatine and creatinine [Biochemistry](https://durgical.com/en/biochemistry/) · Topic # Creatine, phosphocreatine and creatinine Creatine is made from three amino acids and stores quick energy in muscle as phosphocreatine. Its waste product, creatinine, shows how well the kidneys filter. Updated 2026-11-01 ## Key facts - Three amino acids: arginine and glycine form guanidinoacetate (AGAT, mainly kidney); SAM methylates it to creatine (GAMT, mainly liver). - Creatine travels in blood and enters muscle and brain through the creatine transporter (SLC6A8); 95 % of the body's creatine is in skeletal muscle. - Creatine kinase: creatine + ATP ⇌ phosphocreatine + ADP; at rest it stores energy, and in the first seconds of effort it regenerates ATP. - About 2 % of creatine and phosphocreatine turns into creatinine each day by a non-enzymatic cyclisation; creatinine output is proportional to muscle mass. - Creatinine is filtered freely by the glomerulus (with a little tubular secretion) and not reabsorbed, so serum creatinine is used to estimate GFR. ## In detail - 1. Kidney: L-arginine:glycine amidinotransferase (AGAT, gene GATM) moves the amidino group of arginine to glycine → guanidinoacetate + ornithine. - 2. Liver: guanidinoacetate methyltransferase (GAMT) adds a methyl from SAM → creatine + S-adenosylhomocysteine; this is one of the biggest consumers of methyl groups. - 3. Creatine kinase isoenzymes: CK-MM (skeletal muscle), CK-MB (heart), CK-BB (brain) and a mitochondrial form that links ATP made in mitochondria to phosphocreatine (the phosphocreatine shuttle). - 4. Phosphocreatine lasts about 10 seconds of maximal effort, bridging the gap until glycolysis speeds up. - 5. Creatinine is formed at a steady rate, so a 24-hour urine creatinine checks that a collection is complete. - 6. Dietary creatine (meat, fish) and supplements reduce the body's own synthesis (AGAT is repressed by creatine). **Also called** Creatine synthesis, Creatine kinase shuttle ## Clinical notes - Serum creatinine rises when GFR falls, but only after about half of kidney function is lost; it also depends on muscle mass, age and sex. - Creatine deficiency syndromes (AGAT, GAMT, transporter) cause intellectual disability and seizures; brain MR spectroscopy shows a missing creatine peak. - CK in blood rises with muscle damage (rhabdomyolysis, myositis, muscular dystrophy); CK-MB was used for myocardial infarction. ## Related conditions - [Guanidinoacetate methyltransferase (GAMT) deficiency](https://durgical.com/en/conditions/guanidinoacetate-methyltransferase-deficiency/) - [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/) - [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/) - [Duchenne muscular dystrophy](https://durgical.com/en/conditions/duchenne-muscular-dystrophy/) ## Related - [Creatine](https://durgical.com/en/biochemistry/molecules/creatine/) - [Creatinine](https://durgical.com/en/biochemistry/molecules/creatinine/) - [S-adenosylmethionine (SAM)](https://durgical.com/en/biochemistry/molecules/s-adenosylmethionine/) - [Molecules derived from amino acids](https://durgical.com/en/biochemistry/topics/molecules-derived-from-amino-acids/) - [ATP (adenosine triphosphate)](https://durgical.com/en/biochemistry/molecules/atp/) - [Isoenzymes](https://durgical.com/en/biochemistry/topics/isoenzymes/) - [Urea cycle](https://durgical.com/en/biochemistry/pathways/urea-cycle/) - [Creatinine and estimated glomerular filtration rate (eGFR)](https://durgical.com/en/biochemistry/topics/creatinine-and-estimated-glomerular-filtration-rate/) - [Creatine kinase (CK) and CK-MB as lab tests](https://durgical.com/en/biochemistry/topics/creatine-kinase-and-ck-mb-as-lab-tests/) ## Test yourself Think of the answer, then tap the question to see it. ## Which three amino acids are needed to make creatine? Arginine and glycine (forming guanidinoacetate) and methionine, as SAM, which gives the methyl group. ## Where are the two steps of creatine synthesis mainly carried out? AGAT acts mainly in the kidney and GAMT mainly in the liver. ## Why does serum creatinine depend on muscle mass? Creatinine forms non-enzymatically from muscle creatine and phosphocreatine at a steady rate, so more muscle means more creatinine. ## What reaction does creatine kinase catalyse? Creatine + ATP ⇌ phosphocreatine + ADP; during intense effort it runs backward to regenerate ATP. ## What does brain MR spectroscopy show in creatine deficiency syndromes? A missing or very low creatine peak. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/creatine-phosphocreatine-and-creatinine/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Guanidinoacetate methyltransferase deficiency: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/guanidinoacetate-methyltransferase-deficiency/) (MedlinePlus, US National Library of Medicine, 2026); [GATM: Glycine amidinotransferase, mitochondrial (human)](https://www.uniprot.org/uniprotkb/P50440/entry) (UniProt, 2026); [GAMT: Guanidinoacetate N-methyltransferase (human)](https://www.uniprot.org/uniprotkb/Q14353/entry) (UniProt, 2026); [Creatinine blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003475.htm) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011). [← All of biochemistry](https://durgical.com/en/biochemistry/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. 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