Argininosuccinic acid is a non-proteinogenic amino acid that is an important intermediate in the urea cycle.

[2] Some cells synthesize argininosuccinic acid from citrulline and aspartic acid and use it as a precursor for arginine in the urea cycle (or citrulline-NO cycle), releasing fumarate as a by-product to enter the TCA cycle.

The enzyme that catalyzes the reaction is argininosuccinate synthetase.

[3][4] Argininosuccinic acid is a precursor to fumarate in the citric acid cycle via argininosuccinate lyase.

[5] Carbamoyl phosphateL-citrullineL-ornithineUreaL-aspartateL-argininosuccinateL-arginineFumarate