Exopeptidase that catalyzes the hydrolytic cleavage of multi-L-arginyl-poly-L-aspartic acid (cyanophycin; a water-insoluble reserve polymer) into aspartate-arginine dipeptides. [L-4-(L-arginin-2-N-yl)aspartate](n) + H2O = [L-4-(L-arginin-2-N-yl)aspartate](n-1) + L-4-(L-arginin-2-N-yl)aspartate kcat is 16.5 sec(-1) for cyanophycin. Optimum pH is 7.5. Optimum temperature is 35 degrees Celsius. Homodimer. Belongs to the peptidase S51 family.