Cyclic carbon flux

The Krebs cycle, also known as the tricarboxylic acid or citric acid cycle, operates within the mitochondria it fuUy oxidizes the two carbon atoms in acetyl-CoA to COj. During the oxidation process, acetate groups are carried on a 4-carbon molecule, oxaloacetate. The fact that oxaloacetate is regenerated at the end of the process makes this pathway a cycle. Availability of the carrier is important in regulating the carbon flux aroimd the cyclic pathway. 

It is generally accepted that cyanobacterial TCA cycle is not very active under phototrophic conditions. A recent study further proved that it operates in a bifurcated way [112]. However, the bifurcated pattern switches to a dominantly cyclic pattern by introducing an ethylene-forming enzyme from Pseudomonas. Ethylene can be sustainably and efficiently produced from 2-oxoglutarate while also activating the TCA cycle metabolism. The enhanced flux via the remodeled TCA is 37% of the total fixed carbon which is higher than the 13% found in wild type. This result indicates that the metabolic malleability of the cyanobacterial TCA cycle depends on what it produces. 

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