Cyanophycin is a non-protein, non-ribosomally produced amino acid polymer composed of an aspartic acid backbone and arginine side groups. Cyanophycin is largely insoluble under physiological conditions and is accumulated in the form of granules in the cytoplasm during phosphate or sulfur starvation, generally in the early and mid-stationary phase. It is used as a nitrogen- and possibly carbon-storage compound and also serves as a dynamic buffer for fixed nitrogen in cyanobacterial heterocysts. Nitrogen and carbon are mobilized from cyanophycin by intracellular cyanophycinase in the form of aspartate-arginine dipeptides.Cyanophycin is synthesized from arginine and aspartate in an ATP-dependent reaction catalyzed by a single enzyme, cyanophycin synthetase. Cyanophycin is of potential interest to biotechnology as a source of polyaspartic acid.
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