Arginine inhibits the arginine biosynthesis rate-limiting enzyme and leads to the accumulation of intracellular aspartate in Synechocystis sp. PCC 6803.

Cyanobacteria are oxygen-evolving photosynthetic prokaryotes that affect the global carbon and nitrogen turnover. Synechocystis sp. PCC 6803 (Synechocystis 6803) is a model cyanobacterium that has been widely studied and can utilize and uptake various nitrogen sources and amino acids from the outer environment and media. l-arginine is a nitrogen-rich amino acid used as a nitrogen reservoir in Synechocystis 6803, and its biosynthesis is strictly regulated by feedback inhibition. Argininosuccinate synthetase (ArgG; EC 6.3.4.5) is the rate-limiting enzyme in arginine biosynthesis and catalyzes the condensation of citrulline and aspartate using ATP to produce argininosuccinate, which is converted to l-arginine and fumarate through argininosuccinate lyase (ArgH). We performed a biochemical analysis of Synechocystis 6803 ArgG (SyArgG) and obtained a Synechocystis 6803 mutant overexpressing SyArgG and ArgH of Synechocystis 6803 (SyArgH). The specific activity of SyArgG was lower than that of other arginine biosynthesis enzymes and SyArgG was inhibited by arginine, especially among amino acids and organic acids. Both arginine biosynthesis enzyme-overexpressing strains grew faster than the wild-type Synechocystis 6803. Based on previous reports and our results, we suggest that SyArgG is the rate-limiting enzyme in the arginine biosynthesis pathway in cyanobacteria and that arginine biosynthesis enzymes are similarly regulated by arginine in this cyanobacterium. Our results contribute to elucidating the regulation of arginine biosynthesis during nitrogen metabolism.