Pathways of carbon flux in gluconeogenesis.

Although the classical pathways of gluconeogenesis are now well understood, they alone do not account for the rate of incorporation of isotopes from labeled precursors into glucose or for the distribution of isotopes within the glucose molecule. Additional factors include the rate of glycerol metabolism relative to the rate of triosephosphate isomerase, isotope dilution in the Krebs cycle, equilibration by the fumarase reaction, flux through pyruvate dehydrogenase, and recycling via pyruvate kinase. The importance of the latter two reactions is greatest when the gluconeogenetic flux is low.