Phosphoglucose isomerase is important for carbon distribution over central carbon metabolic pathways in cyanobacteria

= 0.3). Effector studies revealed two potent inhibitors: erythrose 4-phosphate (E4P) and 6-phosphogluconate (6PG). E4P, an intermediate of the regenerative CBB (rCBB) cycle, inhibited SynPGI at μM concentrations and 6PG, a metabolite of the oxidative pentose phosphate pathway, inhibited the enzyme at mM concentrations. Kinetic modeling indicated that a mixed-type inhibition model best describes the inhibitory effects of both metabolites. Enzymatic, structural and phylogenetic analyses reveal that cyanobacterial SynPGI closely resembles plastidic PGIs from plants and suggest that it may function as a metabolic control node, integrating environmental and intracellular signals to fine-tune carbon flux and enhance metabolic efficiency in Synechocystis.