Creatine synthesis and metabolism

The formation of GAA is the rate-limiting reaction facilitated by inhibition of AGAT activity via negative feedback through creatine and competitive inhibition through ornithine.
The major proportion of creatine is taken up from the blood via the creatine transporter.
The brain is capable of producing minor amounts of creatine.
Intracellular creatine is reversibly converted into creatine-phosphate through the action of creatine kinase.
Creatine/creatine phosphate (CK) and ADP/ATP together with CK represent a high-energy phosphate shuttle exiting mainly in brain and muscle.
Creatinine results from the nonenzymatic conversion of creatine and is excreted in the urine with a constant daily turnover of 1.5% of body creatine.
An individual's daily creatinine excretion is directly proportional to total body creatine and in particular to muscle mass (ie, 20 to 25 mg/kg/24 hours in children and adults).

AGAT: arginine:glycine amidinotransferase; GAMT: guanidinoacetate methyltransferase; CRTR: creatine transporter; ATP: adenosine triophosphate; CK: creatine kinase; ADP: adenosine diphosphate.

Reproduced from: Dunbar M, Jaggumantri S, Sargent M, et al. Treatment of X-linked creatine transporter (SLC6A8) deficiency: Systematic review of the literature and three new cases. Mol Genet Metab 2014; 112:259. Illustration used with the permission of Elsevier Inc. All rights reserved.

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Creatine synthesis and metabolism