(DEC 2013 GU)
69. If the product of an enzyme binds to the enzyme- substrate complex to exhibit its activity through a decrease in both K_m and V_max, this type of inhibition is called
(1) competitive inhibition
(2) non-competitive inhibition.
(3) uncompetitive inhibition.
(4) partially-competitive inhibition.

The correct answer is (4) Reaction cannot be favorably biased by increasing substrate concentration.

Introduction

Competitive inhibition is a key biochemical concept describing how enzymes can be regulated or inhibited by molecules resembling the substrate. This inhibition is characterized by reversible active site binding and competition between inhibitor and substrate molecules. A widespread misconception is that the reaction rate cannot be favorably biased by increasing substrate concentration—the contrary is true. This article clarifies the features of competitive inhibition, highlighting why increased substrate levels can restore reaction rates despite inhibition.

Features of Competitive Inhibition

• Substrate Mimicry: The inhibitor resembles the substrate structurally and binds the active site.

• Inhibition Mechanism: By occupying the active site, the inhibitor blocks substrate binding.

• Reversibility: Inhibitor binding is reversible; increasing substrate concentrations outcompete the inhibitor.

• Kinetic Effect: Increases apparent KmKm, indicating reduced substrate affinity, but VmaxVmax remains unchanged.

Why Option (4) is False

• Increasing substrate concentration increases likelihood of substrate binding over inhibitor, overcoming inhibition.

• This reversibility distinguishes competitive inhibition from other types like non-competitive inhibition.

• Thus, reaction rates can be favorably biased (increased) by raising substrate levels even during competitive inhibition.

Comparative Table

Real-World Implications

• Many drugs function as competitive inhibitors allowing for dosage-dependent therapeutic effects.

• Laboratory experiments exploit this principle to study enzyme kinetics and inhibition.

Conclusion

The false statement about competitive inhibition is that the reaction cannot be favorably biased by increasing substrate concentration. Competitive inhibition can be overcome by adding more substrate, restoring enzymatic activity, making option (4) inaccurate.