Figure 7. Nitrogen metabolism in Anabaena PCC 7120 heterocysts. The main components involved in nitrogen fixation and assimilation include nitrogenase (nif-genes) and glutamine synthase (GS, glnA). 2-oxoglutarate is synthezised from oxaloacetate and acetyl-CoA by the incomplete TCA-cycle, of which the aconitate hydratase (EC 4.2.1.3) and isocitrate dehydrogenase (EC 1.1.1.42) are shown. Together with glutamine, 2-oxoglutarate is exported to vegetative cells while glutamate is imported.