Question

Which one of the following statements regarding enzyme inhibition is correct ?

• A. Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme
• B. Competitive inhibition is seen when a substrate competes with enzyme for binding to an inhibitor protein
• C. Noncompetitive inhibition of an enzyme can be overcome by adding large amount of substrate
• D. Noncompetitive inhibitors often bind to the enzyme irreversibly

Answer 1

Answer: (A)

Competitive inhibition is a reversible inhibition where inhibitor competes with the normal substrate for the active site of enzyme. A competitive inhibitor is usually chemically similar to the normal substrate and therefore, fits into the active site of an enzyme and binds with it. The inhibition is thus due to substrate analogue. The enzyme, now cannot act upon the substrate and reaction products are not formed. Hence, action of an enzyme may be reduced or inhibited. Since a competitive inhibitor occupies the site only temporarily, the enzyme action is not permanently affected. The activity of succinate dehydrogenase is inhibited by malonate and is the most common example of competitive inhibition.