PHRD5025 Biochem - Lecture 6 - Enzymes II

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daynuhmay
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PHRD5025 Biochem - Lecture 6 - Enzymes II
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2013-09-23 20:58:33
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enzymes
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enzymes
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  1. small molecules that interfere with catalysis, slowing, or halting enzymatic reactions
    inhibitors
  2. 3 types of inhibition
    • 1) reversible, competitive
    • 2) reversible, noncompetitive
    • 3) irreversible
  3. Line-Weaver Burk plot


    1/(Michaelis-Menten)
  4. binding/association constant
    Ka=
  5. dissociation constant
    Kd=
  6. stronger binding -> ___ [ES] -> higher ___; lower ____
    increased; Ka; Kd
  7. [S]=Kd
    half of the enzyme binding sites are occupied by the substrate
  8. involves inhibitor binding at an enzyme's substrate binding (active) site
    competitive inhibition
  9. a substance that directly competes with a normal substrate for the enzyme's binding site
    competitive inhibitor
  10. type of inhibitor that resembles normal substrate
    competitive inhibitor
  11. particularly effective inhibitors, bc they bind stronger to the enzyme rather than the substrate
    transition state analogs
  12. products of enzymatic reactions
    may accumulate and compete with substrates for binding to the enzyme

    (cell activity control mechanism)
  13. type of inhibition that reduces the concentration of free enzyme
    competitive inhibition
  14. a function of the inhibitor's concentration and its affinity for the enzyme

    factor by which [S] must be increased to overcome a competitive inhibitor

    1+ [I]/KI
  15. KI
  16. how does the degree of competitive inhibition vary?
    by the fraction of enzyme that has bound inhibitor
  17. does the inhibitor affect the enzyme's turnover number?
    NO
  18. how does  affect a double reciprocal plot in competitive inhibition?
    • changes the slope
    • doesn't change the y-intersect
  19. what competes with methanol for binding to alcohol dehydrogenase?
    ethanol
  20. what do HIV protease inhibitors do?
    bind to the active site and mimic the tetrahedral transition state
  21. disease involving elevated concentrations of uric acid in the blood and tissues, and underexcretion of urine
    gout
  22. target for treating gout
    inhibition of the conversion of purines to uric acid by xanthine oxidase
  23. type of inhibitor that binds to the enzyme-substrate complex, but not at the substrate binding site
    uncompetitive inhibitor
  24. upon binding, this inhibitor induces a conformational change which makes the enzyme inactive
    uncompetitive inhibition
  25. do uncompetitive inhibitors need to resemble the substrate?
    NO
  26. for uncompetitive inhibition: ____ Vmax; ____ Km
    lower; same
  27. how does ' change the double-reciprocal plot during uncompetitive inhibition?
    unchanged slope; changed y-intercept
  28. mixed inhibition
    involves inhibitor binding to both the free enzyme and the enzyme-substrate complex
  29. how does  change the double-reciprocal plot during mixed inhibition?
    both slope and y-intercept change
  30. irreversible inhibitor
    • bind covalently to the enzyme, or
    • destroy a functional group that is required for the enzyme's activity, or
    • form a highly stable non-covalent association
  31. mechanism by which penicillin interferes with the synthesis of peptidoglycan
    attacks the key Ser residue in the active site of transpeptidase, generating a very stable covalent adduct, and making the enzyme inactive
  32. fluorouracil
    • creates dead-end covalent complex with thymidylate synthase
    • cancer drug

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