<p> Cyanophycin is an insoluble storage polymer for carbon, nitrogen, and energy, found in most Cyanobacteria. The polymer has a backbone of L-aspartic acid, with most Asp side chain carboxyl groups attached to L-arginine. The polymer is made by this enzyme, cyanophycin synthetase, and degraded by cyanophycinase. Heterologously expressed cyanophycin synthetase in <taxon tax_id="562">Escherichia coli</taxon> produces a closely related, water-soluble polymer with some Arg replaced by Lys. It is unclear whether enzymes that produce soluble cyanophycin-like polymers in vivo in non-Cyanobacterial species should be designated as cyanophycin synthetase itself or as a related enzyme. Cyanophycin synthesis is analogous to polyhydroxyalkanoic acid (PHA) biosynthesis, except that PHA polymers lack nitrogen and may be made under nitrogen-limiting conditions [<cite idref="PUB00015470"/>].</p> Cyanophycin synthetase