Biochemical pathways and enzymes involved in carbon and nitrogen metabolism in Cyanothece ATCC51142. Pathways were generated by mapping labeled proteins onto known metabolic pathways. Each arrow shows the direction of the reaction. Protein symbols in red indicate higher synthesis in the light or during the transition to dark. Protein symbols in blue indicate higher synthesis in the dark cycle or during the transition to light. Incomplete TCA cycle in cyanobacteria [42, 63] provides 2-OG as a carbon skeleton for nitrogen assimilation through GS-GOGAT cycle converting 2-OG to glutamate which is utilized either for the biosynthesis of heme, chlorophyll, and phycobilin or purines and pyrimidines. The excess glutamate (or carbamoyl-P) is recycled through the urea cycle. The pathway also provides different intermediate metabolites as precursors for the biosynthesis of lipids (such as DHAP), fatty acids (Mal-CoA) and leucine and isoleucine (pyruvate and acetyl-CoA). The maximum levels of synthesis of these enzymes as determined by RIA are shown in parenthesis.