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Thread: Nature has engineered the structures of control enzymes so that their activities may be modulated rapidly by small changes in the concentrations of certain key effector molecules.

  1. #1 Nature has engineered the structures of control enzymes so that their activities may be modulated rapidly by small changes in the concentrations of certain key effector molecules. 
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    Nature has engineered the structures of control enzymes so that their activities may be modulated rapidly by small changes in the concentrations of certain key effector molecules.

    Discuss this statement with reference to phosphofructokinase

    I need help with this question from a past paper. Just need help with how to address this question.
    Thankyou


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  3. #2  
    exchemist
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    You poor sod - what a dull question....zzzzzzzzz........

    Presumably there is something, or a class of somethings, that switches this tedious-sounding enzyme on or off. Thank God I didn't do biochemistry.

    Sorry, I'm a bit p1ssed on a Sunday night. Better go to bed.


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  4. #3  
    Moderator Moderator Cogito Ergo Sum's Avatar
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    PFK is regulated by both allosterism and substrate-cycling (the latter falls beyond the scope of your question).

    In essence, this enzyme is regulated by ATP and ADP/AMP (Mansour, T.E. et al., 1968) and switches between the T (low affinity for ligand) and R state (high affinity for ligand).

    Each PFK subunit (there are four) has two binding sites for ATP (substrate and inhibition site).
    ATP binds the substrate site in both states, but the inhibition site is solely occupied by ATP when PFK is in the T state.
    However, F2,6P (fructose-2,6-biphosphate) preferentially binds to PFK when the enzyme is in the R state.
    As such, high levels of [ATP] shift the equilibrium towards the T state in such a way that F2,6P has a decreased affinity for PFK.

    On the other hand, when AMP and ADP bind to the enzyme, they shift the equilibrium to the R state and therefore favor the binding of F2,6P to PFK.


    Source:
    Voet, J.G., Voet D. & Pratt, C.W. (2012), "Principles of Biochemistry, 4th Ed.", Wiley, pp. 498-499


    PS: This answer is incomplete. It is up to you to fill in the missing pieces.
    Last edited by Cogito Ergo Sum; September 2nd, 2013 at 08:15 AM. Reason: PS required.
    "The only safe rule is to dispute only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong."

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