Question

True About Noncompetitive antagonist :

• A. Km remains same, Vmax decreases
• B. Km remains same, Vmax decreases
• C. Km decreases, Vmax increases
• D. Km increases, Vmax increases

Answer 1

The Correct Option is A

A noncompetitive antagonist is a type of inhibitor that decreases the maximum velocity (Vmax) of an enzyme-catalyzed reaction without affecting the Michaelis constant (Km). This occurs because the inhibitor binds to an allosteric site rather than the active site.

Here's how it works:

• Binding Site: The noncompetitive antagonist binds at a site other than the active site, called an allosteric site, which changes the enzyme's shape.
• Effect on Km: Since it does not compete with the substrate for the active site, the Km, which is a measure of the substrate's affinity to the enzyme, remains unchanged.
• Effect on Vmax: The Vmax, or the maximum rate of the reaction, decreases because the binding of the antagonist reduces the number of active enzyme molecules, making it impossible for the reaction to reach the same rates even if substrate concentration is increased.

The correct option from the given choices is: Km remains same, Vmax decreases.