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 E. coli 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. This model makes the designation as cyanophycin synthetase. Cyanophycin synthesis is analogous to polyhydroxyalkanoic acid (PHA) biosynthesis, except that PHA polymers lack nitrogen and may be made under nitrogen-limiting conditions. [Cellular processes, Biosynthesis of natural products]
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