Enzyme Inhibitors and Classification of Enzyme Inhibition
Enzyme inhibitors (I) are molecular agents that interfere with catalysis, slowing or halting enzymatic reactions. They stop the fitting of substrates into the enzyme’s active site.
This can be represented as,
E + S ↔ ES → P + E (E=enzyme, P=products)
I + E ↔ EI → X (P does not form)
- E = Enzyme
- S= Substrate
- I= Inhibitors
- P = Product
Examples of inhibitors include toxins, poisons, pesticides, and antibiotics.
Classes of Enzyme Inhibition:
There are two kinds of enzyme inhibition-
- Reversible Inhibition and
- Irreversible Inhibition.
Again there are three kinds of Reversible Inhibition —
- Competitive Inhibition
- Uncompetitive Inhibition and
- Non-competitive Inhibition.
Classes of Reversible Inhibition:
- Competitive Inhibition: Inhibitor (I) binds only to Enzymes (E), but not to the enzyme-Substrate complex (ES) and inhibits the Enzymes (E) to function is known as the Competitive Inhibition. It is a real kind of Inhibition. It happens in real for an Enzyme. A competitive inhibitor is reversible and has a structure like a substrate to fit the active site of the enzyme. So Competitive competes with the substrate for the active site of the enzymes. Once It fit with the active site of an Enzyme it makes an Enzyme-Inhibitor complex (EI), the Substrate can’t bind with the Enzyme. So the Inhibition takes place. But it is a reversible process so the Enzyme-Inhibitor complex (EI) breaks down and again enzyme becomes functional.
- Uncompetitive Inhibition: Inhibitor (I) binds only to Enzyme-Substrate complex (ES), not to Enzymes (E) and inhibits the enzymes to function is known as the Uncompetitive Inhibition. This is a hypothetical situation for a true enzyme that has never been documented, but which makes a helpful contrast to competitive inhibition.
Noncompetitive Inhibition: Inhibitor (I) binds to both the Enzymes (E) and the Enzyme-Substrate complex (ES) and hence inhibits the Enzymes (E) to function is known as the Noncompetitive Inhibition. In this case, the Inhibitor binds with the Enzymes as well as the Enzyme-Substrate complex (ES). So the enzymes can’t be functional anymore. But this process also reversible so the enzyme can be functional again but there is some inhibition in the reaction of the enzyme. Hence the reaction rate is affected by the inhibitors.