Cyanophycin synthase (L-aspartate-adding) (EC 6.3.2.29, CphA, CphA1, CphA2, cyanophycin synthetase, multi-L-arginyl-poly-L-aspartate synthase) is an enzyme with systematic name cyanophycin:L-aspartate ligase (ADP-forming).^{[1][2][3][4][5][6]} This enzyme catalyses the following chemical reaction

ATP + [L-Asp(4-L-Arg)]n + L-Asp ${\displaystyle \rightleftharpoons }$ ADP + phosphate + [L-Asp(4-L-Arg)]n-L-Asp

This enzyme requires Mg²⁺ for activity. All enzymes known to have this activity also catalyze the addition of arginine, i.e. cyanophycin synthase (L-arginine-adding) activity. It is structurally similar to Muramyl ligases.