Side-by-Side Comparison
| Feature | Competitive Inhibition | Non-Competitive Inhibition |
|---|---|---|
| Inhibitor binding site | Active site (same as substrate) | Allosteric site (different from active site) |
| Structural resemblance to substrate | YES — structurally similar | NO — no resemblance |
| Effect on Km | INCREASES (apparent Km rises) | UNCHANGED |
| Effect on Vmax | UNCHANGED | DECREASES |
| Overcome by excess substrate? | YES | NO |
| Mechanism | Competes with substrate for active site | Conformational change reduces catalytic efficiency |
| Classic example | Malonate inhibits succinate dehydrogenase | Heavy metals (, ) inhibiting enzymes |
| Drug design example | Statins (HMG-CoA reductase inhibitors) | Many allosteric drugs |
Michaelis-Menten Kinetic Effects
Competitive Inhibition:
- Km increases → curve shifts RIGHT on v vs [S] plot
- Vmax same → both curves reach same plateau
- At very high [S] → inhibitor outcompeted, activity restored
Non-Competitive Inhibition:
- Km same → curve position unchanged horizontally
- Vmax decreases → curve plateau is LOWER
- No amount of substrate can restore Vmax
NEET Memory Hook
- Competitive → Can be overcome by excess substrate → Changes Km (increases) → Vmax unchanged
- Non-competitive → Not overcome by substrate → No change in Km → Vmax decreased