Protocol Online logo
Top : Forum Archives: : Biochemistry

Allosteric and noncompetive inhibition - (Dec/24/2008 )

Note: This is not a homework question. This is part of a study effort for a big test coming up soon.

What's the difference between noncompetitive inhibition and allosteric inhibition?????????

The progress I made on this problem: In Deborah Goldberg's AP Biology, "In noncompetitive inhibition, the enzyme contains more than one active site and the substrates do not resemble each other. However, when one substrate binds to one active site, the second active site is blocked and the second substrate is prevented form binding to the enzyme. Which substrate binds to the enzyme is random and a function of the concentration of each substrate." However, "Allosteric inhibition involves two active sites, one for a substrate and the other for an inhibitor. The enzyme oscillates between two conformations, one active, one inactive. When the inhibitor binds to one active site, the enzyme undergoes a conformational change, the active site for the substrate is altered, and the enzyme cannot catalyze the reaction..." Clearly, in this book, allosteric and noncompetitive inhibition sound very similar. Can someone explain to me the difference between noncompetitive inhibition and allosteric inhibition?????????????????????

All insight offered to this problem is greatly appreciated and I thank you in advance.

-thewax-

I believe the difference is that either substrate in noncompetitive inhibition is catalyzed (altered, transformed) by the enzyme, whereas in allosteric inhibition, if the inhibitor binds, no reaction occurs at all -- the enzyme is inactive.

-HomeBrew-

Thanks!!!!!! smile.gif

But my book says that the operon is an example of noncompetitive inhibition, but it is not really altered (I mean the repressors and the inducers, etc.).....

-thewax-

QUOTE (thewax @ Dec 24 2008, 08:11 PM)
Thanks!!!!!! smile.gif

But my book says that the operon is an example of noncompetitive inhibition, but it is not really altered (I mean the repressors and the inducers, etc.).....


My opinion:

Noncompetitive inhibition: There might be single or multiple active site on the enzyme. The enzyme catalyzes its own natural substrate (endogenous compound). But when let say we consumed exogenous compound (drugs, poison etc) which can fit the enzyme active site but no formation of product (antagonist). The compound strongly bind to the enzyme active site that the increase of the enzyme natural substrates would not expel the exogenous compound from active sites.

Allosteric inhibition: It is part of enzyme regulation. Like glycolysis pathways. U can read how phosphofruktokinase is regulated by its own product. The regulation will maintain body homeostasis.

TQ smile.gif

-kent19-