Question

In competitive inhibition
A. Km of the enzyme is increased
B. Vmax of the enzyme is increased
C. Vmax of the enzyme is not changed
D. Inhibitor molecule is structurally similar to the substrate molecule of the enzyme
Choose the correct answer from the option given below:

• A. A & B only
• B. B & C only
• C. B & D only
• D. A, C & D only

Hint:

Enzyme Inhibition Profiles:
Competitive $\rightarrow K_m \uparrow$, $V_{\max}$ unchanged.
Non-Competitive $\rightarrow K_m$ unchanged, $V_{\max} \downarrow$.
Uncompetitive $\rightarrow K_m \downarrow$, $V_{\max} \downarrow$.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Competitive enzyme inhibition occurs when a substrate-mimicking inhibitor competes for the free active site, increasing apparent $K_m$ without altering $V_{\max}$.
Key Formula or Approach:
\[ K_m^{\text{app}} = K_m \left(1 + \frac{[I]}{K_i}\right) > K_m \quad | \quad V_{\max}^{\text{app}} = V_{\max} \]

Step 2: Detailed Explanation:
Kinetics and mechanics of Competitive Inhibition:
1. A (True): Apparent $K_m$ increases ($K_m^{\text{app}} = \alpha K_m$) because higher substrate concentrations are required to displace the inhibitor.
2. C (True): $V_{\max}$ remains unchanged because saturating $[S]$ completely outcompetes the inhibitor for active site binding.
3. D (True): The competitive inhibitor is a structural analogue mimicking the size, shape, and charge of the natural substrate.
Thus, statements A, C, and D are correct.

Step 3: Final Answer:
Therefore, the correct choice is A, C & D only, corresponding to option (D).