enzyme catalysis control

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Author:
embryo
ID:
97848
Filename:
enzyme catalysis control
Updated:
2011-08-21 22:06:16
Tags:
enzymes
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Description:
MS1/Mod 1: biochem; control of enzyme catalysis
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  1. ATCase
    allos enz that cat condensation of aspartate and carbamoyl phosphate to N-carbomoylaspartate
  2. CTP
    • final prod of pyrimidine biosynth
    • feedback inhibitor of ATCase; binds to allos site of ATCase
  3. Catalytic subunit of ATCase
    cat act; not affected by CTP; trimer; 6 active sites
  4. Regulatory subunit of ATCase
    no cat act; binds CTP, dimer
  5. PALA
    N-(phosphonaacetyl)-L-aspartate: bisubstrate analog of ATCase; can show active site of ATCase
  6. R state
    relaxed state; high aff for substrate; capable of binding substrate and is fully active
  7. T state
    tense state: inactive and low aff for substrate
  8. Why do allosteric enz not display a hyperbolic curve?
    display sigmoidal shape invece perche' the transition from inactive T state to active R state w/ increase in subst conc. Subst binding in one site will increase enz act of remaining sites....cooperativity

    OR: sigmoidal curve is composite of two Michaelis-Menton curves; one for T state and one for R state; at low conc of subst, enz inactive form and resemble T state but as subst conc increase, enz goes to R state. Combining two curves gives an int which is sigmoidal
  9. How does CTP inhibit ATCase?
    stabilizes inactive T state; now harder for enz to go to R state
  10. ATP
    allos act of ATCase; binds to same site as CTP, but stabilizes R state, increases subst aff, and increases act
  11. Heterotropic effect
    binding of a small molecule effects binding of some other chemically distinct mol
  12. Homotropic effect
    binding a sm mol affects binding of other sm mol of same type (i.e. subst)
  13. Concerted model
    all or none model; no combo of R and T states; subunits are either ALL in R state or ALL in T state

    binding one subst mol converts all other subunits to R state--->only positive cooperativity is poss; if one subunit loses a mol then others will NOT lose their mol
  14. Sequential model
    enz can have any combo of R and T states simultaneously; conf change in one subunit may increase of decrease aff of other subunits--->allows for BOTH pos and neg cooperativity
  15. How does high ATP affect ATCase activity?
    high ATP means there are a lot of purines in the env, therefore more pyrimidines need to be made to balance out; final end prod of ATCase is CTP which is used in pyrimidine synth--->overall: high ATP stim ATCase act to make more CTP
  16. Isozyme
    diff enz that cat same rxn; can differ in struct, kinetics, and regulatory prop; allow for fine-tuning of rxns
  17. Lactate dehydrogenase (LDH)
    • 2 forms: M and H
    • tetramer
  18. M4
    (M) subunit of LDH; M4 func in anaerobic env
  19. H4
    (H) subunit of LDH; H4 func in aerobic env (aka heart); allos inhib by pyruvate
  20. How can measure of M4 and H4 be used clinically?
    remember properties of M4 and H4 (M4 is anaerobic and H4 is aerobic); if there is an imbalance of M:H then there is something wrong

    per esempio: if there is more H4 than H3M in blood, then indication of myocardial infarction bc H4 has gotten out of heart (aerobic) into anaerobic env
  21. Covalent modification
    reversible attachment of donor molecules that affect enz func; can shift equil of active and inactive states
  22. Phosphorylation
    • donor: ATP
    • ex prot: glycogen phosphorylase
    • func: gluc homeostasis; E transduction
  23. Acetylation
    • donor: acetyl CoA
    • ex prot: histones
    • funct: DNA packaging, transC
  24. Myristoylation
    • donor: myristoyl CoA
    • ex prot: Src
    • func: STP
  25. ADP-ribosylation
    • donor: NAD
    • ex prot: RNA pol
    • func: transC
  26. Farnesylation
    • donor: farnesyl pyrophosphate
    • ex prot: Ras
    • func: STP
  27. gamma-carboxylation
    • donor: HCO-3
    • ex pro: thrombin
    • func: blood clotting
  28. Sulfation
    • donor: 3'-phosphoadenosine-5'-phosphosulfate
    • ex prot: fibrinogen
    • func: blood-clot formation
  29. Ubiquitination
    • donor: ubiquitin
    • ex prot: cyclin
    • func: control of cell cycle
  30. Protein kinase
    enz that cat phosphorylation of prot by transferring gamma (terminal) phosphate group of ATP to OH groups of Ser, Thr, Tyr on targets
  31. Phosphatases
    cat de-phosphorylation of proteins
  32. cAMP-dep prot kinase
    • Ser/Thr kinase
    • act by cyclic nucleotides
  33. cGMP-dep prot kinase
    • Ser/Thr kinase
    • act by cyclic nucleotides
  34. Ca2+ calmodulin prot kinase
    • Ser/Thr kinase
    • act by Ca2+ and calmodulin
  35. Phosphorylase kinase /glycogen synthase kinase 2
    • Ser/Thr kinase
    • act by Ca2+ and calmodulin
  36. AMP-act kinase
    • Ser/Thr kinase
    • act by AMP
  37. Protein kinase C
    • Ser/Thr kinase
    • act by diacylglycerol
  38. Abl kinase
    • autoinhibited form is NOT phosphorylated
    • phosphorylation of activation loop (Tyr 412) causes allosteric stabilization of R state
  39. Proteolytic activation
    conversion of inactive enz into act one via proteolysis
  40. Zymogens/proenzymes
    inactive precursors; act by cleavage of one or a few peptide bonds; irreversible

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