When acetyl-CoA enters the cycle, and the acetate (two carbons) is combined with the four-carbon molecule oxaloacetate. Citrate is then produced which is rearranged to isocitrate.In the first oxidation, isocitrate is oxidized to 2-oxoglutarate (α-ketoglutarate) in which a carbon is lost as CO2 and NAD+ reduced to NADH. In the second oxidation, 2-oxoglutarate is converted to succinyl-CoA leaving carbon as CO2 and NAD+ reduced to NADH. The product is attached to coenzyme A and reaction is catalyzed by oxoglutarate dehydrogenase. Succinate and CoA bond is broken in which the energy released is used to drive the phosphorylation of a GDP to GTP. The γ -phosphate groups can be swapped between nucleotides, so GTP can be used to regenerate ATP from
