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P hospho f ructo k inase PFK

P hospho f ructo k inase PFK. http://oregonstate.edu/instruct/bb450/fall2011/stryer7/16/figure_16_16.jpg. Glycolysis. Phosphofructokinase catalyses the third reaction of glycolysis The reverse reaction in Gluconeogenesis is catalyzed by fructose-1,6-bisphosphatase. Regulation of glycolysis.

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P hospho f ructo k inase PFK

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  1. PhosphofructokinasePFK http://oregonstate.edu/instruct/bb450/fall2011/stryer7/16/figure_16_16.jpg

  2. Glycolysis • Phosphofructokinase catalyses the third reaction of glycolysis • The reverse reaction in Gluconeogenesis is catalyzed by fructose-1,6-bisphosphatase

  3. Regulation of glycolysis • There are three largely negative ΔG reactions in glycolysis which are used to mediate flux • These reactions are all kinases: catalysis of reactions involving the addition or removal of phosphate groups Reaction 1 – Hexokinase Reaction 3 – PFK Reaction 10 – Pyruvate kinase Voet, Voet, Pratt 4th Ed. Fig 15-21

  4. Why PFK is the major flux mediator • The hexokinase step is often bypassed as all glucose-1-phosphate created from glycogenolysis can be converted directly to glucose-6-phosphate via phosphoglucomutase enzyme. • The pyruvate kinase reaction is the last one and therefore is not used to mediate glycolysis directly, it is used to mediate the overall metabolism of metabolites. Voet, Voet, Pratt 4th edition fig 16-5

  5. Structure of PFK • Phosphofructokinase is a homotetramer that displays allostery. • Has two unique dimer-dimer interfaces • Four substrate-binding interfaces • Four effector –binding interfaces • Is regulated by allosteric ligands that alter the binding of the substrate

  6. Allosteric interactions • Allosteric activation • ADP • AMP • Fructose-2,6-bisphosphate • Allosteric inhibition • Phosphoenolpyruvate • ATP • At low metabolic demand, ATP concentrations are high, ADP and AMP concentrations are low and there PFK is allosterically inhibited. Conversely, during exercise when ATP concentrations decrease subsequently increasing the concentrations of ADP and AMP, PFK in allosterically activated to promote the uptake of metabolites and the production of ATP • Pyruvate kinase indirectly regulates metabolic flux through glycolysis by inhibiting PFK with the build up of phosphoenolpyruvate. • PFK-2 can be targeted to increase F2,6P concentrations in order to allosterically activate PFK when there is a metabolic demand.

  7. At low levels of ATP the forward reaction is much more favorable. In vivo studies show that low [ATP] account for <10% increase in metabolic flux however PFK activity can change 100-fold. This is accounted for the preferential binding of AMP and ADP to the R-state. http://oregonstate.edu/instruct/bb450/fall2011/stryer7/16/figure_16_17.jpg

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