lecture14_10_21_08parta

lecture14_10_21_08parta - Lecture 14 Overview: -glycolysis...

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1 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 Exam 2 (one week from Thurs): you may bring a 5 × 8 'cheat sheet' same rules as the last exam apply. 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
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2 Recall from lecture 13: Step 3) Phosphorylation of F-6P to F-1,6BP investment of second ATP Δ 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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3 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
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lecture14_10_21_08parta - Lecture 14 Overview: -glycolysis...

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