Proteins and Enzymes

ID #1043

I was wondering why it was that increasing substrate concentration has no effect on the ability of noncompetitive inhibitors to block reactions. Since noncompetitive inhibitors can be unbound, wouldn't an influx of substrate increase the probability of producing a product like it would competitive inhibitors?


You're right about one thing -- a non-competitive inhibitor can (and eventually will) become unbound. But unless you remove or inactivate the inhibitor molecule, there's nothing keeping the same or another inhibitor molecule from jumping right back into that site. So without changing the level of functional inhibitor, for all intents and purposes the enzyme will be inactivated. Then the issue becomes this: If an enzyme can't convert 100 substrate molecules to product, then how could it be expected to covert 1000 substrate molecules? It couldn't be. Raising the level of natural substrate has no effect on the rate of reaction catalyzed by a non-covalently inhibited enzyme.

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