Requires Mg2+?for activity. Both this enzyme and EC?6.3.2.29, cyanophycin synthase (L-aspartate-adding), are required for the elongation of cyanophycin, which is a protein-like cell inclusion that is unique to cyanobacteria and acts as a temporary nitrogen store [2]. Both enzymes are found in the same protein but have different active sites [2]. Both?L-Asp and?L-Arg must be present before either enzyme will display significant activity [2]. Canavanine and lysine can be incoporated into the polymer instead of arginine [2].