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Types of Enzyme Inhibition with Mnemonics
- October 26, 2024
- Posted by: Namrata Chhabra
- Category: Enzyme kinetics Enzymology Learning resources Library Quick Revision Series Quick revisions Quick revisions USMLE Content
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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.” |
Author:Namrata Chhabra

With over 38 years of experience as a Medical Educator, Medical Biochemist, and Researcher, Dr. Namrata Chhabra has a proven track record of leading and contributing to clinical, academic, and research initiatives that advance medical science and education. She holds an M.B.B.S., an M.D. and Ph.D. in Medical Biochemistry, and a Master's in Health Professions Education (MHPE). She is also a FAIMER Fellow, a prestigious recognition of her excellence in medical education and research.
Currently, she serves as the Associate Dean of Admissions, Chair of the Admissions Committee, and a Professor of Biochemistry at the American University of Antigua College of Medicine (AUACOM). In this role, she oversees the academic quality, curriculum development, faculty development, accreditation processes of the college, and student recruitment. She also teaches and mentors medical students, conducts and supervises biomedical and educational research projects, and publishes and presents her findings in national and international journals and conferences. Additionally, she is the author of three comprehensive textbooks on Medical Biochemistry, which are widely used by medical students and professionals. She is passionate about improving the health outcomes of communities and individuals by fostering a culture of innovation, collaboration, and excellence in medical education and research.