Figure 1

Schematic representation of the central carbon metabolism network, which was implemented in the multi-level kinetic model of Synechocystis 6803.

Differences in enzymes involved in central carbon metabolism between Synechococcus 7942 and Synechocystis 6803 were included. Blue indicates isozymes in Synechocystis 6803 that are missing in Synechococcus 7942. Green indicates isozyme in Synechocystis 6803 with higher amount of isozymes in comparison to Synechococcus 7942. Yellow indicates the newly added oxidative phase of the oxidative pentose phosphate pathway, which is active also during the day (HC condition) in Synechocystis 6803, in contrast to Synechococcus 7942. Transaldolase was omitted due to low flux¹¹, and phosphogluconolactonase was neglected for simplicity. White indicates the metabolites whose concentrations are available in the metabolome data set. The model includes the Calvin-Benson cycle, glycogen synthesis (sink from glucose-6-phosphate), photorespiratory pathways, glycolysis, the oxidative pentose pathway and sink reactions (representing the adjacent pathway and the calculation of biomass production). The reversibility of a particular reaction is indicated by two small arrows. Red squares indicate the major carbon reallocation nodes for changing CO₂ levels. Purple indicates the involved enzymes: RuBisCO–ribulose-1,5-bisphosphate carboxylase oxygenase, PGK–phosphoglycerate kinase, GAP–glyceraldehyde-3-phosphate dehydrogenase, TPI–triose-phosphate isomerase, ALDO–aldolase, FBPase–fructose-1,6 bisphosphatase, PFK–phosphofructokinase, TKT–transketolase, SBPase–sedoheptulose-1,7 bisphosphatase, RPI –phosphopentose isomerase, PPE–phosphopentose epimerase, PRK –phosphoribulokinase, GPI–glucose-6-phosphate isomerase, G6PD–glucose-6-phosphate dehydrogenase, PGD–phosphogluconate dehydrogenase, PGPase–phosphoglycolate phosphatase, PKET–phosphoketolase, GOX –glycolate oxidase, SGAT–serineglyoxylate transaminase, HPR –hydroxypyruvate reductase, GLYK –glycerate kinase, AGT–alanine-glyoxylate transaminase, TSS –tartronatesemialdehyde synthase, TSR–tartronatesemialdehyde reductase, SHMT–serine hydroxymethyltransferase, GLOX –glyoxylate oxidase, PSAT*–phosphoserine transaminase (3-phosphoglycerate dehydrogenase is, for simplicity, not implemented), PGM–phosphoglycerate mutase, ENO–enolase. Open book symbol indicates an involvement of metabolite in other reaction(s).