A network of reactions adopted from the glycolysis pathway and the pentose phosphate pathway is shown in which the labeled carbon isotope rearranges to different carbon positions throughout the network of reactions. The network starts with fructose 6-phosphate (F6P), which has 6 carbon atoms with a label C at carbon position 1 and 2. 1,2- C F6P becomes two glyceraldehyde 3-phosphate (G3P), one 2,3- C T3P and one unlabeled T3P. The 2,3- C T3P can now be reacted with sedoheptulose 7-phosphate (S7P) to form an unlabeled erythrose 4-phosphate (E4P) and a 5,6- C F6P. The unlabeled T3P will react with the S7P to synthesize unlabeled products. The figure demonstrates the use of stable isotope labeling to discover the carbon atom rearrangement through reactions using position specific labeled compounds.