How do competitive and noncompetitive inhibitors affect enzyme function?

2 Answers
Sep 18, 2015

Let's start an enzyme with 'U'


U is just an example..see the open which sides upward as an active site of enzyme that means every specific molecules attach to it will be processed

Competitive reacts with that active site by attach to it. Example A is the right molecule for U and B is not. B will compete A to attach that active site and the U becomes unavailable for A to attach and process it. Sometimes the competitor will get processed to but many times it just competes and not get processed.. This thing has been used widely for medicine

Non-competitive reacts not with the active site. You see the U has the down(opposite the upward site) the non-competitive inhibitor will attach to it and change the active site for example to be an O so the A molecule cannot attach to it

Sep 20, 2015

competitive inhibitors compete with the actual ligand for the binding site in protein whereas non-competitive inhibitors do not.


is a substance that reduces or decreases the activity of an enzyme. It inhibits the proper functioning of enzyme.

Competitive inhibitors
competitive inhibitors are those which mimics the shape of the actual substrate and binds to the active site.

Figure below explains the functioning, substrate comes and binds to enzyme undergoes product formation and releases the site, making it available for new substrate to come and bind.

when a competitive inhibitor is present which mimics the substrate and binds with the enzyme but is not converted to any product and competes for the enzyme active site with actual substrate.
in simple terms enzymes activity decrease in presence of Competitive inhibitor

in the figure below the enzyme kinetics is low at low concentration of substrate but as the substrate amount increases its activity also reaches back to its normal

Non-competitive inhibitors
Non-competitive inhibitors do not compete for the active site with substrate but does not allow substrate to bind at the active site.

These are actually of two types
1. Allosteric as shown in first figure BELOW, they bind at different position but actually causes change in the active site so new substrate moity cannot bind.
2. in the second figure BELOW the substrate is sterically hindered, blocking the active site so as substrate can not interact with the enzyme.
Figure 1
Figure 2 (sorry couldn't find any better resolution)

in simple terms Non-Competitive Inhibitors do not allow the substrate to bind at the active site.

in the figure below the enzyme activity is low at low concentration of substrate but as the substrate amount increases its activity cannot reach the normal level unlike the competitive inhibitor.