Question

What causes competitive inhibition?

Answer 1

Competitive inhibition is caused by a reversible inhibitor(competitive one) which is selected by binding site of enzyme but can't activate the catalytic site.

Explanation:

Sometime a compound has the same structure to that of a normal substrate and fits at the binding portion of the active site. Thus in this way the enzyme can't be available to a normal substrate.

So, due to structural similarity with a normal substrate, a competitive inhibitor is selected by the binding site but is not able to activate the catalytic site. As it occupies the binding site, the binding site remains unavailable for a normal substrate. So, there is not any kind of product formation. This is known as competitive inhibition.

Example:
Malonic acid has structural similarity with succinic acid. Succinic acid is specific substrate for succinic dehydrogenase(enzyme). But in some cases, malonic acid fits in binding site of succinic dehydrogenase as a competitive inhibitor but is not able to activate the catalytic site so products are not formed.

`Note:`
Active site is divided into two sites:

Binding site : This site holds proper substrate and fits it as enzyme-substrate or ES complex.

Catalytic site : This part of active site transforms the substrate into products which means it is vital for catalytic activity of enzyme.

Hope it helps...