Argininosuccinate lyase arginine synthesis

Arginine and fumarate are produced from argininosuccinate by the cytosolic enzyme argininosuccinate lyase. In the final step of the cycle arginase cleaves urea from aspartate, regenerating cytosolic ornithine, which can be transported to the mitochondrial matrix for another round of urea synthesis. 

Arginine or citrulline in concentration in excess of the optimal can inhibit both argininosuccinate synthetase or argininosuccinate lyase in tissue cultures (S6). Whether this is applicable to the conditions of synthesis of the urea in liver is uncertain. a-Methylaspartic acid also specifically inhibits argininosuccinate synthetase (B7, C4, SIO). 

---