7V-acetylglutamate

Two other types of regulation control the urea cycle allosteric activation of CPSI by 7V-acetylglutamate (NAG) and induction/repression of the synthesis of urea cycle enzymes. NAG is formed specifically to activate CPSI it has no other known function in mammals. The synthesis of NAG from acetyl CoA and glutamate is stimulated by arginine (Fig. 38.15). Thus, as arginine levels increase within the liver, two important reactions are stimulated. The first is the synthesis of NAG, which will increase the rate at which carbamoyl phosphate is produced. The second is to produce more ornithine (via the arginase reaction), such that the cycle can operate more rapidly. 

F. 38.15. Activation of carbamoyl phosphate synthetase I (CPSI). Arginine stimulates the synthesis of 7V-acetylglutamate, which activates CPSI. 

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