Cyanophycin synthase (<small>L</small>-arginine-adding) (, CphA, CphA1, CphA2, cyanophycin synthetase, multi-<small>L</small>-arginyl-poly-<small>L</small>-aspartate synthase) is an enzyme with systematic name cyanophycin:<small>L</small>-arginine ligase (ADP-forming). This enzyme catalyses the following chemical reaction:
This enzyme requires Mg<sup>2+</sup> for activity. This enzyme requires Mg<sup>2+</sup> for activity. All enzymes known to have this activity also catalyze the addition of aspartate, i.e. cyanophycin synthase (L-aspartate-adding) activity. It is structurally similar to Muramyl ligases.