Question

What is the difference between competitive and irreversible inhibitors?

What is the difference between a suicide inhibitor and a competitive inhibitor?

Answer 1

ANS:

Enzyme inhibition:

It is defined as a substrate which binds with the enzyme and brings about a decrease in catalytic activity of that enzyme. The enzyme inhibition broadly classified into three categories.

A. Reversible inhibition.

B. Irreversible inhibition.

C. Allosteric inhibition.

1. ANS: Difference between competitive and irreversible inhibition:

Competitive inhibition:

Competitive inhibition is a reversible inhibition. In this the inhibitor (I) closely resembles the real substrate (S) is regarded as a substrate analogue. The inhibitor competes with substrate and binds at the active site of the enzyme but does not undergo any catalysis.

In competitive inhibition the Km value increases, whereas V max remains unchanged.

Ex: Succinate dehydrogenase is inhibited by malonate.

Irreversible inhibition:

The inhibitor binds covalently with the enzymes and inactivates them, which is irreversible. These inhibitors are usually toxic poisonous substances.

In Irreversible inhibition the V max value decreases, whereas Km remains unchanged.

Ex: Heavy metals like arsenic, cadmium and lead.

2. ANS: Difference between a suicide inhibition and competitive inhibition:

Suicide inhibition:

Suicide inhibition is a special form of irreversible inhibition and it is also known as a mechanism based inhibition. In this the original inhibitor (The structural analogue/competitive inhibitor) is converted to a more potent form by the same enzyme that ought to be initiated. The so formed inhibitor binds irreversibly with enzyme.

Ex: Allopurinol (Used in gout treatment).

Competitive inhibition:

Competitive inhibition is a reversible inhibition. In this the inhibitor (I) closely resembles the real substrate (S) is regarded as a substrate analogue. The inhibitor competes with substrate and binds at the active site of the enzyme but does not undergo any catalysis.

In competitive inhibition the Km value increases, whereas V max remains unchanged.

Ex: Succinate dehydrogenase is inhibited by malonate.