Noncompetitive inhibition and allosteric inhibition

[thewax]

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.

[blcr11]

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.

[thewax]

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?????????