Argininosuccinate synthase
![](/Images/godic/202412/21/Protein_ASS1_PDB_2nz24913.png")
![Reaction catalyzed by argininosuccinate synthetase. Adapted from Goto et al. 2003.[2]](/Images/godic/202412/21/WikiChemdraw4913.png")
![](/Images/godic/202412/21/PDB_1j21_EBI4913.jpg")
![Active site of argininosuccinate synthetase shown with bound citrulline, ATP, and aspartate interacting with select active site residues. Modeled using PyMol from PDB 1J1Z.](/Images/godic/202412/21/Active_site_of_Thermus_thermophilus_argininosuccinate_synthetase_014914.png")
Argininosuccinate synthase or synthetase (ASS; EC6.3.4.5) is an enzyme that catalyzes the synthesis of argininosuccinate from citrulline and aspartate.
ASS is responsible for the third step of the urea cycle and one of the reactions of the citrulline-NO cycle.