tonguo
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what is the effect of positive/negtive allosteric effectors on the Km and Vmax of an enzyme? I am talking about allosteric enzyme, not michaelis-menton enzyme.
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| mjl1717
Forum Hero
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1) You are right allosteric enzymes are Completely different from Michaelis
Menton kinetics! (Sigmoid curve like hemoglobin)
2)Often one active site of an allosteric enzyme molecule can affect another
active site on the same molecule
3)Km must be determined empirically by determining Vmax and V at
different substrate concentrations( this is the Michaelis Menton constant
which is a reference point for enzymes measured in
millimoles/per liter.
4)Trying to put this together Id say a positive allosteric affector would
increase substrate binding thus increasing Vmax and Km
5) A negative allosteric affector would decrease Vmax and Km
6)The velocity of an allosteric enzyme rxn depends on the concentraion of
both the substate and the modifier.
7) An allosteric effector can alter the affinity of the enzyme for its substrate
or modify the maximal catalytic activity of the enzyme or both.
Hope this helps. Comments please.
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| tonguo
Forum Senior
Topics: 29
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thanks a lot mjl1717 for ur great answer. if u have kaplan notes, u can actually found a figure showing the changes imposed upon enzyme by allosteric effectors. it is fig I-8-9 in the 2002 edition notes. but it is not perfectly clear. here is what i figured out from the notes:
negative effector definitely incr Km (decr affinity); it seems to decr Vmax, too, but not so significantly. therefore, it has both the characteristics of competitive and noncompetitive inhibitors.
positive effector does the opposite.
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