Question

What happens in case of competitive inhibition of an enzyme?

• A. V${}_{max}$ is increased
• B. K${}_m$ is increased
• C. The extent of inhibition remains the same in high substrate concentrations
• D. None of the above

Answer 1

Answer: (B)

K${}_m$ is increased

A competitive inhibitor is one which competes with the substrate molecules for the active site of enzyme. The competitive inhibitor has structural similarity with the substrate and is complementary to the active site of the enzyme, hence it interferes with the substrate binding to the enzyme molecule. When enough substrate is present the probability that an inhibitor molecule will bind is minimized and the reaction exhibits normal V${}_{max}$. However the K${}_m$ (substrate concentration at which rate is half the maximum) will increase in the presence of inhibitor. This effect on the apparent K${}_m$ and the absence of an effect on V${}_{max}$ is diagnostic of competitive inhibition.

Thus, the correct answer is option B.