Competitive inhibitor

Competitive inhibitor
In biochemistry one distinguishes two ways in which a molecule may block the action of an enzymes: competitive and noncompetitive inhibition.

competitive inhibitor
A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics.
complement fixation ...

competitive inhibitors are molecules that bind to the same site as the substrate - preventing the substrate from binding as they do so - but are not changed by the enzyme.

Competitive inhibitors can bind to E, but not to ES. Competitive inhibition increases Km (i.e., the inhibitor interferes with substrate binding), but does not affect Vmax (the inhibitor does not hamper catalysis in ES because it cannot bind to ES).

Non-competitive Inhibitors
Chemical does not have to resemble the substrate
Binds to enzyme other than at active site
This changes the enzyme's active site and prevents access to it ...

B. there is a competitive inhibitor present
C. there is a non-competitive inhibitor present
D. the allosteric enzyme is locked in an inactive conformation ...

Lovastatin A competitive inhibitor of HMG-coa reductase, the key regulatory enzyme in cholesterol biosynthesis; used therapeutically to lower cholesterol levels. Also called mevinolin.

at sufficiently high concentration of the normal ligand inhibition is lost: the Km is altered by the competitive inhibitor, but the vmax remains the same.

See also: Enzyme, Substrate, Action, Lysis, Enzymes