Regulation of Glycolysis/Gluconeogenesis Citric Acid Cycle / TCA cycle / Kreb’s cycle

  • View

  • Download

Embed Size (px)


Regulation of Glycolysis/Gluconeogenesis Citric Acid Cycle / TCA cycle / Kreb’s cycle Electron Transport Chain (Oxidative Phosphorylation). 3 major points of regulation of glycolysis. Hexokinase Phosphofructokinase-1 Pyruvate kinase. -32.9. -24.5. Each regulatory reaction - PowerPoint PPT Presentation

Text of Regulation of Glycolysis/Gluconeogenesis Citric Acid Cycle / TCA cycle / Kreb’s cycle

  • Regulation of Glycolysis/GluconeogenesisCitric Acid Cycle / TCA cycle / Krebs cycleElectron Transport Chain (Oxidative Phosphorylation)

  • 3 major points of regulationof glycolysisHexokinase


    Pyruvate kinase-32.9-24.5-26.4Each regulatory reactionis held far from equilibrium (large DG)

    Each regulatory step in glycolysisis coordinately regulated withgluconeogenesis Substrate Cycle**

  • Each regulatory step in glycolysis is coordinately regulated with gluconeogenesis

    Futile/Substrate cycle:ATPADPPiH2OSum: ATP + H20 ADP + Pi* If allowed to occur at the same time utilization of ATP without useful metabolic work being done Cycles provide important means of regulationGlycolysisGluconeogenesis

  • HexokinaseMuscleLiverMuscle High affinity for glucose

    Usually saturated and working at maximal rate

    Inhibited by glucose 6-phosphate (product inhibition)

    Liver much lower affinity (higher Km)for glucose.

    Allows liver to process high levels of glucose

    Not inhibited by glucose 6-phosphate

  • Coordinate Regulation of PFK-1 and FBPase-1 (regulation by energy state of cell)PFK-1 inhibited by signals of adequate energy suppliesATP CitrateActivated by signals of low energy suppliesADPAMP

    FBPase-1 Inhibited by signals of low energy suppliesAMP

    * Commitment step of glucose into glycolysis

  • Hormonal regulation of glycolysis and gluconeogenesis mediated by fructose 2,6 bisphosphateF26BP activates PFK-1 (binds to allosteric site and increases its affinity for its substrate (F6-phosphate)F26BP inactivates FBPase 1 (decreasesits affinity for its substrate (F1,6 BP))

  • Where does F2,6 Bisphosphate come from?

    Hormonal regulation of PFK-2 / FBPase-11 bifunctional NZ with 2 separate activities regulated by insulin and glucagon

    **Regulation of NZ is by phosphorylation**Formation of F26BPBreakdown of F26BPGlucagon stimulates phosphorylation of PFK-2/FBPase 2-Activation of FBPase-2 activity (phosphatase)-Reduction of F26BP- Glycolysis GluconeogenesisInsulin stimulates dephosphorylation of PFK-2/FBPase 2-Activation of PFK2 activity (Kinase) -Increase in F26BP - Glycolysis Gluconeogenesis

  • Enzymes of glycogen metabolism are regulated by allostericand hormonal mechanismsGlycogen PhosphorylaseGlycogen SynthaseActivation G6PAMP

    Inhibition ADP, PiATP, G6P, Glucose Signals of high energy supply (G6P, ATP) stimulate glycogen synthesis andinhibit glycogen breakdown.

    Signals of low energy supply (ADP, AMP) stimulate glycogen breakdownand inhibit glycogen synthesisAllosteric Regulation

  • Hormonal Regulation of glycogen synthesis and breakdown Covalent ModificationGlucagonActivation of PKA (via cAMP)P of phosphorylase kinase P of Glycogen phosphorylaseAndP of Glycogen synthaseStimulation of glyc breakdown

    Inhibition of glyc synthesis(A)(IA)Glycogen breakdownInhibition of Glycogen breakdownActivation of phosphoprotein phosphatase -1

    DeP of Glycogen phosphorylase Phosphorylase kinase(A)(IA)(IA)

  • Glucose enters hepatocytes through transporter

    2) Synthesis of glycolytic enzymesFed State - Insulin 3) inactivation of GSK3 and activation of PP1Activate glycogen synthase and inactivate glycogen phosphorylase Glycolysis Glycogen synthase Glycogen breakdownFasting State - glucagon Activation of PKA through cAMP 1) Activates phosphorylase kinase glycogen phosphorylase 2) Inactivates glycogen synthase

    3) Phosphorylates PFK-2/FBPase-2 in F2,6BP 4) Inactivates pyruvate kinaseGlycolysis Glycogen synthase Glycogen breakdown

  • GlycolysisGlucose PyruvateTransition/Prep PhaseNADH


    C1C2C3C4ATPsynthaseATPCitricAcid CycleElectron TransportOverview of Steps Acetyl - CoACytoplasmMitochondriaPyruvate

  • 2 C acetyl group combines with 4 C oxaloacetate to yield 6 C citrate Citrate (C6)Isocitrate (C6)a-ketoglutarate (C5)Succinyl co-A (C4)Succinate (C4)Fumarate (C4)MalateOxaloacetate (C4)C02CoASHC02NADHGTP / ATPCoASHFADH2NADH2 Acetyl-CoACoASHSubstrate level phosphorylation1 Glucose2 pyruvatesNADHPyruvate Dehydrogenase1-2- Carbons lost in pathway as C02 -These Cs are not from acetyl-coA

    3- Oxaloacetate consumed in the 1st step is regenerated in the last.

    4- Energy produced is transferred as energy-rich electrons to NAD+ to yield NADH or to FAD+ to yield FADH2

    5- 2 rounds of Cycle yields: 4 CO2, 6 NADH, 2 FADH2, and 2 ATP

    6- CAC is amphibolic has a role in oxidation of carbohydrates and provides precursors for other pathways (ex AA metabolism)Citric Acid Cycle

  • Regulation of Citric Acid Cycle1- Pyruvate Dehydrogenase (irreversible) Product/Feedback inhibition Covalent Modification (Phosphorylation = inactive)

    2- Isocitrate Dehydrogenase 4- Citrate synthase NADH CitrateNADH and Acetyl CoA compete with NAD+ and CoA for binding sites competetive feedback inhibitionProduct/FeedbackInhibition****All function far from equilibrium (- G)

    3- a-Ketoglutarate Dehydrogenase A- Substrate Availability (oxaloacetate;acetyl-CoA)B- Product InhibitionC- Competitive Feedback InhibitionRegulated enzymes of CAC1- PD2- ID3-KD4-CS

  • Electron Transport Chain

  • MatrixIntermembrane spaceNADHNAD+MembraneSolubleCoenzyme QFADFeSCyt. C O2 + 2H+ H204H+4H+2H+Complex IComplex IIComplexIVFADH2FAD+FMNFeSSuccinateFumarateCytsFeSComplex IIICytsCu1- Electrons from NADH and FADH2 are passed through redox centers of 4 membrane bound complexes and 2 membrane soluble electron shuttles

    2-During electron transfer, protons are translocated from the matrix into the intermembrane space (Complex 1, Complex III, and Complex IV)

    3- Final reduction is of molecular O2

    4- Electrons from NADH yield 2.5 ATP; Electrons from FADH2 yield 1.5 ATP

  • Proton Motive Force - Chemiosmotic theory

    H+H+H+++++++++++++------------------Low pHHigh pHH+lllllVVATPIntermembrane spaceOuter membraneInner membraneStorage of energy as a proton/voltage gradient across a membrane1- In ETC, the transport of H+ from low [H+] to high [H+] requires energy (ENDERGONIC)

    2- Discharge of proton is EXERGONIC Free energy of discharge of proton gradient is harnessed by ATP synthaseOxidative phosphorylationF1Fo

  • 02 ConsumptionTimeDNPTimeDNPATP SynthesisTimeDNPNo drugInhibitor addeduncoupler addedElectron transport and ATP synthesis are coupledATP synthesis requires discharge of proton gradient: Proton gradient cannot be discharged without synthesis of ATP:Proton gradient is established by electron transporting complexes.Electrons flowing through ETC; O2 is being consumed;ATP is being synthesized Inhibitor of ETCStops flow of electrons;No proton pumping; No proton motive force;No longer consuming O2;No longer making ATP Uncoupler of ETCDestroys proton gradient; No stored energy for ATP;DOES NOT stop electron flow;Oxygen still being consumed