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Noncompetitive inhibition and allosteric inhibition

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Noncompetitive inhibition and allosteric inhibition

Postby thewax » Wed Dec 24, 2008 11:14 pm

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.
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Postby blcr11 » Thu Dec 25, 2008 12:17 pm

The two terms overlap to some extent. All "non-competitive" means is that the inhibitor lowers Vmax without changing Km. You can't read much mechanism into it. The notion of competitive, non-competitive, mixed-competitive are all kinetic behaviors.

An allosteric site is a binding site distinct from the substrate binding or active site. Allosteric binders can activate as well as inhibit. Usually, there is some kind of conformational change of the protein involved. It need not alter just the conformation of the active site, though certainly allosteric effectors do such things. Sometimes (maybe even most of the time) a non-competitive inhibitor works by binding allosterically, but all you really know when you identify an inhibitor as "non-competitive" is that it reduces the active concentration of enzyme without changing the affinity of the enzyme toward substrate. But that's all you know.
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Postby thewax » Thu Dec 25, 2008 11:21 pm

Thanks!!!!!!!!! :)

So just to clarify on the wording: Allosteric sites can either house activators or inhibitors. And noncompetitive sites are what? Are there any other defining characteristics of allosteric sites?????????
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Re:

Postby jon123 » Sat Sep 03, 2016 9:05 pm

Tragusthewax wrote:Thanks!!!!!!!!! :)

So just to clarify on the wording: Allosteric sites can either house activators or inhibitors. And noncompetitive sites are what? Are there any other defining characteristics of allosteric sites?????????


It's true that Allosteric sites can either house activators or inhibitors!
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Postby leesajohnson » Sat Sep 24, 2016 4:30 am

Non-competitive inhibition and allosteric inhibition-
Non-competitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate. The inhibitor may bind to the enzyme whether or not the substrate has already been bound, but if it has a higher affinity for binding the enzyme to one state or the other; it is called a mixed inhibitor.

Allosteric inhibition is very important because it controls how much an enzyme will work. Allosteric inhibitors and activators are like on & off keys for these molecular robots. Thus the activity of an enzyme can be controlled by a different chemical. If the organism wants to shut down an enzyme, it will release an inhibitor, & if it wants to stimulate the enzyme into higher production, then it will release an activator.
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