Question

How does a competitive inhibitor change the Km and Vmax values for an enzyme such as Penicillin?

Answer 1

Ans. The primary function of an enzyme inhibitor is to decrease the activity of the enzyme to which it binds.This is done by either binding to the enzyme thus stopping the subtrate to enter the active site of enzyme or by preventing the enzyme to catalyse chemical reaction. These enzyme inhibitors are grouped as irreversible inhibitors and reversible inhibitors.

Competitive inhibition is an example of reversible inhibition, where weak non-covalent bonds are formed by the binding of inhibitors and enzymes.For example, ionic bonds,hydrogen bonds etc. Since there is no chemical bonds formed and no chemical reaction is undergone , their formation and removal are rapid processes. In this type of inhibition the value of Vmax does not change because increased amount of substrate swamp the inhibtor, thus allowing the enzyme to ignore the inhibitor at high subtrate concentration. Whereas, the Km value increases because it accpets more substrates inorder to achieve Vmax/2 value of the competitively inhibited reaction.

Hence, Penicillin being a competitive inhibitor will increase the Km value,keeping the Vmax value unchanged.