| Type of Inhibition | Effect on Vmax and Km | Reversible / Irreversible | Examples | Mnemonic |
| Competitive (Inhibitor competes with substrate for the active site) |
Vmax: Unchanged Km: Increased |
Reversible | 1) Statins – inhibit HMG-CoA Reductase (cholesterol-lowering) 2) PABA – inhibits Pteroyl Synthase (antibiotic) 3) Captopril – inhibits ACE (antihypertensive) 4) Oxamate – inhibits Lactate Dehydrogenase (poison) 5) Methotrexate – inhibits Dihydrofolate Reductase (anticancer) 6) Dicoumarol – inhibits Epoxide Reductase (anticoagulant) 7) Succinate Dehydrogenase – inhibited by Malonate (poison) |
“Some People Can Often Manage Daily Stress.”
(Statins, PABA, Captopril, Oxamate, Methotrexate, Dicoumarol, Succinate Dehydrogenase |
| Noncompetitive (Inhibitor binds away from active site) |
Vmax: Decreased Km: Unchanged |
Reversible / Irreversible | 1) Fluoride – inhibits Enolase (prevents glucose breakdown) 2) Arsenate – inhibits PDH and -SH enzymes (poison) 3) Cyanide – inhibits Cytochrome Oxidase (poison) 4) Aspirin – inhibits Cyclooxygenase (anti-inflammatory) |
“Find All Clinical Applications.” (Fluoride, Arsenate, Cyanide, Aspirin) |
| Suicidal (Mechanism-Based) (Inhibitor activated by enzyme to stop it) |
Vmax: Decreased Km: Increased |
Irreversible | 1) Allopurinol – inhibits Xanthine Oxidase (gout treatment) 2) Fluoroacetate – inhibits Aconitase (rat poison) 3) Penicillin – inhibits Transpeptidase (antibiotic) 4) DFMO – inhibits Ornithine Decarboxylase 5) Deprenyl – inhibits Monoamine Oxidase (Parkinson’s treatment) |
“A Few Pills Deliver Death.”
“A Fantastic Prescription Doesn’t Disappoint.” |
| Allosteric (Inhibitor changes enzyme shape or function) |
Vmax: Reduced (V-type) Km: Increased (K-type) |
Reversible | 1) ATP, Citrate – inhibit PFK-1 (glycolysis) 2) Fr-2,6-bisphosphate – inhibits Fr-1,6-bisphosphatase |
“All Cellular Functions.” (ATP, Citrate, Fr-2,6-bisphosphate) |
| Feedback (Product Inhibition) (Product regulates enzyme) |
Vmax: Decreased Km: Constant |
Reversible depending on product need | 1) Mevalonate and Cholesterol – inhibit HMG-CoA Reductase 2) UTP, CTP – inhibit Aspartate Transcarbamoylase |
“More Useful Control.” (Mevalonate, UTP, Cholesterol) |
| Uncompetitive (Inhibitor binds only to the enzyme-substrate complex) |
Vmax: Decreased Km: Decreased |
Irreversible | Phenylalanine – inhibits Placental Alkaline Phosphatase | “Unique Phenylalanine.” |
