Quantitation of Fluxes in the Gluconeogenic, Glycolytic, and Pentose Phosphate Pathways in Isolated Rat Hepatocytes: Energetic Considerations
For any given substrate mixture and hormonal state, a large number of factors serve to regulate the flow of metabolites along the major pathways of carbohydrate metabolism in hepatocytes. In addition to the amounts of enzymes present, these factors include the intracellular levels of various effectors such as fructose 2,6-bisphosphate, ADP, ATP, and alanine, among others, and the phosphorylation states of several key enzymes. Enzyme levels are subject to long term regulation by dietary and hormonal influences, while effector levels and the phosphorylation state of regulatory enzymes are subject to moment-to-moment changes in hormonal states. While studies on purified enzymes or on tissue homogenates have contributed enormously to our present understanding of the many factors that help regulate metabolic fluxes, a more complete understanding of in vivo regulation of intermediary metabolism requires studies on perfused liver or, in so far as they can be considered as representative of the intact liver, on isolated hepatocytes.
KeywordsPentose Phosphate Pathway Triose Phosphate Isomerase Triose Phosphate Substrate Mixture Futile Cycle
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