noncompetitive inhibition vs. allosteric inhibition:
- Noncompetitive inhibitors bind to a site other than the active site and render the enzyme ineffective.
- Allosteric inhibitors do the same thing. So, how are they different?
It is true that simple mechanistic level non-competitive and allosteric inhibition looks the same but there are several differences. What are they?
- Allosteric inhibition generally acts by switching the enzyme between two alternative states, an active form and an inactive form. It usually works by binding to a sites in a specialized subunit of a the protein, and thus binds at several sites. The more inhibitor that binds, the more then can bind, and vice versa with substrate. The kinetics are REALLY complicated, being cooperative, and non-Michaelis Menton, and are beyond the scope of this course. So a qualitative understanding is all that is needed. Allosteric inhibition is designed into the proteins and represents an important physiological process.
- Noncompetitive inhibition is more of a catch-all for non-physiological inhibition that does not compete with substrate for substrate binding to enzyme. In that, it is defined (and named) from a negative point of view. As described in most texts, a non-competitive inhibitor may bind to a non-substrate site on a protein and distort it to the point of non-functionality, and adding more substrate will not alleviate this inhibition. Or, as another way of thinking about it, it may simply block a catalytic site without interfering with substrate binding.
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