lecture14_10_21_08 - Lecture 14 Overview: -glycolysis...

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Chapter 16: Gluconeogenesis Lecture 14 HW: 16.9, 16.11, 16.14, 16.16, 16.18, 16.20 Overview: -glycolysis regulation -glucose synthesis -gluconeogenesis regulation Control of the glycolytic pathway Two roles of glycolysis: 1) Degrade glucose to generate ATP 2) Provide building blocks for synthetic reactions Enzymes catalyzing irreversible reactions are potential sites of control (hexokinase, phosphofructokinase, and pyruvate kinase Phosphofructokinase; regulation by ATP/AMP 340 kDa tetramer Recall from lecture 13: Step 3) Phosphorylation of F-6P to F-1,6BP investment of second ATP ! G " ° = –14.2 kJ/mol Regulation of phosphofructokinase ATP binds to a specific regulatory site that is distinct from the catalytic site. Binding of ATP lowers the enzyme’s affinity for fructose 6-phosphate. High concentrations of ATP converts the hyperbolic curve into a sigmoidal curve. AMP reverses the inhibitory action of ATP and increases enzyme activity.
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Regulation of phosphofructokinase PFK has two conformational states; R and T. ATP is an allosteric inhibitor and a substrate; each subunit of PFK has two ATP binding sites. The substrate site binds ATP equally well in either conformation, whereas the inhibitor site binds ATP almost exclusively in the T state. F-6P, the other substrate, binds to the R state. Thus, at high concentrations, ATP acts as a heterotropic allosteric inhibitor of PFK by binding to the T state and shifting the equilibrium in favor of the T state and reducing the affinity of F-6P. Regulation of phosphofructokinase low metabolic demand, high [ATP], PFK inhibition; low [ATP], increased ATP synthesis via glycolysis; however, it is not that simple Inhibition of PFK by ATP is relieved by AMP. AMP has preferential binding to the R state. ADP (product of ATP hydrolysis): 2ADP ATP
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lecture14_10_21_08 - Lecture 14 Overview: -glycolysis...

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