Cyanophycin synthase (<small>L</small>-aspartate-adding) (, CphA, CphA1, CphA2, cyanophycin synthetase, multi-L-arginyl-poly-L-aspartate synthase) is an enzyme with systematic name cyanophycin:L-aspartate ligase (ADP-forming). This enzyme catalyses the following chemical reaction
This enzyme requires Mg<sup>2+</sup> 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.