Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
Which of the following statements about reversible enzyme inhibitors are
P. Uncompetitive inhibitors bind only to the enzyme-substrate complex
Q. Non-competitive inhibitors bind only at a different site from the
substrate
R. Competitive inhibitors bind to the same site as the substrate
Options:
(A) P and Q only
(B) P and R only
(C) Q and R only
(D) P, Q and R
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2022 Q.19)**
**1. Governing Concept**:
- **Topic**: Enzyme Kinetics & Reversible Inhibition Modes
- Reversible enzyme inhibition characteristics:
- **Competitive inhibition**: Inhibitor binds exclusively to free enzyme ($E$); increases $K_m^{\text{app}} = \alpha K_m$, leaves $V_{\max}$ unchanged.
- **Uncompetitive inhibition**: Inhibitor binds exclusively to enzyme-substrate complex ($ES$); decreases both $V_{\max}^{\text{app}} = V_{\max}/\alpha'$ and $K_m^{\text{app}} = K_m/\alpha'$.
- **Non-competitive (pure mixed) inhibition**: Inhibitor binds with equal affinity to both $E$ and $ES$; decreases $V_{\max}^{\text{app}} = V_{\max}/\alpha$, leaves $K_m$ unchanged.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: In competitive inhibition, $V_{\max}$ is unaltered.
- **Option (B) is INCORRECT**: In uncompetitive inhibition, $K_m$ decreases, not increases.
- **Option (C) is INCORRECT**: Non-competitive changes $V_{\max}$, not $K_m$.
- **Option (D) is CORRECT**: Accurately describes the verified reversible inhibition parameters.
**3. Final Answer**:
- **Correct Choice**: **D**
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