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ENZYMES

ENZYMES. MALIK ALQUB MD. PHD. Effect of [substrate] on R X Velocity. substrate. substrate. substrate. E. E. E. E. E. E. E. E. E. E. E. E. E. E. E. E. E. E. E. E. E. Effect of [substrate] on R X Velocity. substrate ↑ enzymzs. Saturation. Vmax. E. E. E. E. E. E.

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ENZYMES

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  1. ENZYMES MALIK ALQUB MD. PHD.

  2. Effect of [substrate] on RX Velocity substrate substrate substrate E E E E E E E E E E E E E E E E E E E E E

  3. Effect of [substrate] on RX Velocity substrate↑ enzymzs Saturation Vmax E E E E E E E E E E E E E E E E E E E E E

  4. Effect of [substrate] on RX Velocity Hyperpolicshape v0 = Vmax [S]/(Km + [S])

  5. Effect of [substrate] on RX Velocity 1 • [S] >>> Km, the velocity of reaction is constant and independent of [S] • [S] <<< Km, the velocity of reaction is proportional to [S] • Km= [S] needed to achieve ½ Vmax • = enzyme substrateaffinity 2 3

  6. Enzyme concentration vs. Vmax Incresed enzyme concentration does not affect Km

  7. Double reciprocal plot

  8. Inhibtion of enzyme activity

  9. Example of competativeinhibitor

  10. Inhibtion of enzyme activity

  11. Regulation of Enzyme catalysis • Catalytic activity modified in response to a signal • Increase or decrease • Allow cell to meet changing needs • Energy • Substrate • Product • Usually located early in multi-enzyme reaction pathway

  12. Regulation Mechanisms • Three main mechanisms • Often used in combination • Control enzyme synthesis or degradation • Noncovalent conformational change • Allosteric enzymes • Covalent modification

  13. Allosteric Enzymes • Usually large; multiple subunits • Compare to Hb • Site for allosteric modulator (R = regulatory) generally different from active site (C = catalytic) • Can be positive or negative

  14. E The switch: Allosteric inhibition Allosteric means “other site” Active site Allosteric site

  15. Switching off • These enzymes have two receptor sites • One site fits the substrate like other enzymes • The other site fits an inhibitor molecule Inhibitor molecule Substrate cannot fit into the active site Inhibitor fits into allosteric site

  16. E E The allosteric site the enzyme “on-off” switch Active site Allosteric site empty Conformational change Substrate fits into the active site Inhibitor molecule is present Substrate cannot fit into the active site The inhibitor molecule is absent Inhibitor fits into allosteric site

  17. Kinetics of Allosteric Enzymes • Differ from Michaelis-Menton • Sigmoidal curve • K0.5 instead of KM

  18. Substrate is positive modulator Homotropic Enzyme

  19. Heterotropic Enzyme • Modulator is metabolite • Activator approach hyperbola • Deactivator more sigmoidal

  20. Covalent Modification • Reversible • Phosphorylation • Most common • Catalyzed by kinases • Introduce bulky, charged group • Increase polarity and H-bonding • Repel negative side chains (Asp and Glu)

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