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Allosteric enzymes...?

Discussion in 'MCAT Study Question Q&A' started by LINK1290, Dec 21, 2008.

  1. LINK1290

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    What exactly defines an allosteric enzyme? I've seen many definitions, such as "an enzyme that binds an effector at a site other than the active site," "an enzyme that changes conformation in response to binding an effector," and "an enzyme that has multiple active sites." From what I understand, all of these are true, but even enzymes that exhibit Michaelis-Menten kinetics bind effectors such as inhibitors at sites other than the active site (right?), and a change in conformation follows. Would this make these enzymes "allosteric?"
     
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  3. aquariuscharm

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    Yes, allosteric effectors can either increase or decrease protein activity. The key to the term allosteric is that it usually involves a conformational change of the protein, thereby making the structure of the protein more or less suited to its function/activity (i.e. high affinity -> low affinity state or vice versa).

    From what I've read, the allosteric site is usually separate from the active site.
     
  4. ksmi117

    ksmi117 GEAUX TIGERS!!!
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    I believe an assumption of Michaelis-Menten kinetics is that the enzyme is not allosteric.

    However, if an enzyme does bind to an inhibitor and conformation happens, this is allosteric inhibition, so the enzyme is technically allosteric.
     
  5. isaacmn

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    I am not sure may be I understand that question, I dont think there is any definite terms like... "oh this allosteric enzymes and this is not" . But in a larger sense allosteric really defines the way some enzyme function. Allosteric activators and inhibitors.

    Allosteric activators: enzymatic function that stabilize the E-S complex or the active site. While allosteric inhibitor stabilize the inactive confirmation ( site other than the active site)

    the terms allosteric is also used to define enzymatic binding. In hemoglobin for example when oxygen binds to one side of the heme, there is a positive allosteric effect in which there is an increase affinity for the 3 other oxygen to bind to the heme ( copperative allosteric effect) ---- same as when one of the 02 unloads, there is an increase unloading of the other oxygen atoms. ( high temp, high CO2 and low PH) --rightward shift of dissociation curve ----
     

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