Question

How do enzymes catalyse a chemical reaction in the living system? Explain drug target interaction taking the example of enzyme as target.

Answer 1

Catalytic action of enzymes

• Enzymes are said to be biochemical catalysts, chemically which are just proteins.

• They only catalyze (enhances of a biochemical reaction) the biochemical reactions in the living systems without changing them chemically.

• They are highly specific (binds to a certain substrate only), and this specificity comes from the possession of an active site.

• The shape of the active sites of an enzyme is cavity-like, which is built in such a way that only a specific substrate can fit there. (resembles the system of key-lock fitting).

In the catalytic activity, the enzymes perform two major functions:

(i) The enzyme would orient itself to hold a specific substrate for a chemical reaction.

The active site of enzymes hold that substrate molecule in such a suitable position, so that the reagent (chemical substance with which the substrate reacts) can attack the substrate effectively.

The substrate binds to the active site of the enzyme through a variety of interactions like- hydrogen bonding, van der Waals interaction, or even through dipole-dipole interaction which results in the formation of the enzyme-substrate complex, which later leads to the formation of desired product molecule (produced by substrate-reagent interaction).

(ii) The second function of the enzymes will be providing functional groups (reagents) that will attack the substrate and the chemical reaction will be carried out in the living body.

Drug–target interaction (enzyme being the target)

• Enzymes are the major target for inhibitors like drugs.
• Drugs inhibit the natural activities of enzymes.
• They can block the active site of enzymes which leads to prevention of the binding of the substrate to that binding site, thus drugs inhibit the catalytic activity of the enzyme, which is why they can be called enzyme inhibitors.

There are two ways by which drug-enzyme interaction occurs:

The competitive and non-competitive inhibitions.

(i) Competitive inhibition:

When drugs are competing with a natural substrate for attachment to the active site of enzymes, such drugs are called competitive inhibitors.

(ii) Non-competitive inhibition:

Some drugs do not directly bind to the active sites of the enzymes. Instead, they bind to a different site than the active site, which is called an allosteric site.

This bonding changes the shape of the active site resulting in the substrate not being able to identify it, therefore no enzyme-substrate interaction occurs. This is called non-competitive inhibitions.