Which feature best distinguishes competitive enzyme inhibition from non-competitive inhibition?

Explanation

## Distinguishing Competitive from Non-Competitive Inhibition ### Kinetic Signature of Competitive Inhibition **Key Point:** In competitive inhibition, the inhibitor competes with substrate for the active site. The hallmark kinetic change is an **increase in Km with unchanged Vmax**. **High-Yield:** This pattern arises because: - Higher substrate concentration can overcome inhibition (inhibitor is reversibly displaced) - The enzyme's maximum velocity is unchanged — when substrate concentration is very high, all enzyme molecules bind substrate - Km increases because the apparent affinity for substrate decreases (inhibitor occupies the active site) ### Kinetic Signature of Non-Competitive Inhibition **Key Point:** In non-competitive inhibition, the inhibitor binds to a site OTHER than the active site. Both **Vmax decreases and Km remains unchanged**. **Clinical Pearl:** Non-competitive inhibitors cannot be overcome by increasing substrate concentration because they do not compete for substrate binding — they reduce the number of functional enzyme molecules. ### Comparison Table | Feature | Competitive | Non-Competitive | | --- | --- | --- | | **Binding site** | Active site | Allosteric site | | **Vmax** | Unchanged | Decreased | | **Km** | Increased | Unchanged | | **Reversibility by substrate** | Yes (displaced by ↑[S]) | No | | **Lineweaver-Burk plot** | Lines intersect on y-axis | Lines intersect on x-axis | | **Example** | Statins (HMG-CoA reductase) | Heavy metal poisons (Hg, Pb) | ### Why This Matters **Mnemonic:** **VINK** = **V**max **I**nhibited, **N**ot **K**m (non-competitive); **KINK** = **K**m **I**ncreased, **N**ot **V**max (competitive). [cite:Lehninger Principles of Biochemistry Ch 6]