A comprehensive presentation on Enzymology :Types of Enzyme inhibition & Therapeutic uses for MBBS ,BDS, B Pharm & Biotechnology students to facilitate self- study.

1. Enzymology :Types of Enzyme inhibition &
Therapeutic uses
Dr. Rohini C Sane

2. Enzyme inhibition
Enzyme inhibition
• An Inhibitor –a chemical agent inhibiting /poisoning enzyme
Types of Enzyme inhibition
1. Irreversible Enzyme inhibition
2. reversible Enzyme inhibition

3. Classification
of enzyme inhibition

4. NO PRODUCT FORMATION
Comparison
of
competitive
and non-
competitive
enzyme
inhibition

5. Allosteric Regulation
Change of three dimensional
of enzyme by Allosteric
inhibitor & activator

6. Irreversible inhibition
• Irreversible inhibitor : destroys a functional group on enzyme
necessary for catalytic activity
• eg Di Isopropyl Fluorophosphate(DFP ) inhibits Acetyl choline
esterase
• Iodoacetamide inhibits OH group of serine ,SH group of Cysteine
,Imidazole group of Histidine

7. DFP – inhibits Serine Proteases such as Acetyl Choline
Esterase , Trypsin ,Chymotrypsin ,Elastase
BAL –BRITISH ANTI LEVISITE- Antidote for HEAVY METALS
CYANIDE –Cytochrome Oxidase
FLUORIDE –inhibits Enolase ( removes Mg ⁺⁺/Mn⁺⁺ from the
active site OF enzymes
Irreversible inhibition of enzymes

8. Neurotransmission at synaptic junction by neurotransmitters

9. Irreversible inhibition of Acetyl Choline Esterase
Malathione – an insecticide

10. Inhibition of Neurotransmission at synaptic junction by inhibitors of neurotransmitters-
Donepezil

11. Irreversible inhibition of enzymes with SH group -by Iodoacetamide
enzymes with SH group + Iodoacetamide 
reversible inhibition of enzymes with Chemically modified enzyme ( inactive )

12. Allosteric Regulation
a) Allosteric inhibitor
b) Allosteric activator

13. Allosteric Regulation
a) Allosteric inhibitor
b) Allosteric activator

14. Allosteric Regulation
a) Allosteric inhibitor-binds to an
allosteric site on enzyme &
induces conformation change preventing
Substrate to bind to an active site on enzyme
.Product formation inhibited .

15. Allosteric Regulation
a) Allosteric inhibitor-
three dimensional
change in enzyme
molecule &an active
site of enzyme
deformed.

16. Allosteric & covalent modulation
Activation of many
enzymes involve
Phosphorylation of
enzyme molecule by
Protein Kinases.
Deactivation of many
enzymes is facilitated
by dephosphorylization
of enzyme by
Phosphoprotein
Phosphatases

17. Reversible inhibition of enzymes by Competitive inhibitors
Competitive inhibitors
1. Competitive inhibitors competes with substrate for binding to
active site but once bound substrate cannot be transformed into
product by enzymes.
2. Inhibition by Competitive inhibitors can be reversed by simply
increasing concentration of substrate
3. Competitive inhibitors resembles the normal substrate in 3D
structure
4. E + I = EI

18. NO PRODUCT FORMATION
Comparison of
competitive and
non-competitive
inhibition
Competitive
inhibitors
resembles the
normal substrate in
3D structure
&non-Competitive
inhibitors don’t
resembles the
normal substrate in
3D structure

19. COMPETITIVE INHIBITION ---Competitive inhibitors
1 .competes with
substrate for binding to
active site but once
bound substrate cannot
be transformed into
product by enzymes.
2.Inhibition by
Competitive inhibitors
can be reversed by
simply increasing
concentration of
substrate

20. Changes in Reaction Rate in presence of Competitive & Non –competitive inhibitor
Inhibition by Competitive inhibitors
can be reversed by simply increasing
concentration of substrate& that by
non -Competitive inhibitors
cann’t be reversed by simply
increasing substrate concentration.

21. Competitive inhibition
Competitive inhibitors competes with substrate for binding to active site but once bound
substrate cannot be transformed by enzymes into product.

22. COMPETITIVE INHIBITION OF SUCCINATE DEHYDROGENASE BY FUMARATE ,MALONATE
,OXALO ACETATE

23. Structure of Succinic acid ,Malonic acid & oxaloacetic acid with two carboxylic acid groups
(COOH )& can bind to an active site on succinate dehydrogenase –Competitive inhibitors

24. Clinical significance of Competitive inhibition

25. Clinical significance of Non competitive inhibitors

26. LineWeaver equation & enzyme inhibition

27. THERAPEUTIC USES OF
COMPETITIVE
INHIBITORS-Anti Cancer
Therapy /Drugs for
Myosthenia
Gravis/Antihypertensive

28. Non competitive Inhibition
Characteristics of Non competitive Inhibition
1. Reversible but not reversed by substrate
2. Inhibitor binds at site other than substrate binding site
3. It binds reversibly to both free enzyme & ES complex to form
inactive complex EI & ESI
E + I ↔ EI
ES + I ↔ ESI
4. Inhibitors alter the conformation of E molecule so that reversible
activation occurs
5. They are naturally occurring metabolic intermediates .

29. Non competitive inhibition
Threonine  lsoleucine ( Threonine Dehydratase inhibited by isoleucine-final
product of cascade /pathway ) -feed back inhibition

30. Comparison between competitive & Non competitive inhibition
Criteria competitive Non competitive
Active on Active site May or may not be active at binding
site
Structure of inhibitors Substrate analogs Unrelated molecules
Inhibition reversible Generally irreversible
Excess of substrate Inhibition relieved No effect
Km Increased in presence of
inhibitor
Unchanged in presence of inhibitor
Vmax Unchanged decreased
Significance Therapeutic application Toxicological application

31. Comparison between competitive & Non competitive inhibition
Competition inhibition –Vmax unchanged & Km INCREASED
Non competitive inhibition –Vmax decreased & Km not altered

32. Comparison between competitive & non competitive inhibition
Catalytic site
Regulatory
site
Isoleucine
Binds to
regulatory site on
Threonine
Dehydratase &
functions as non-
competitive
inhibitor

33. Mechanism of action of Aspirin

34. Uncompetitive inhibition of enzymes
Uncompetitive inhibition- inhibitors binds to ES Complex
Vmax & Km decreased eg Alkaline Phosphatase by phenylalanine

35. Suicide Inhibition
Properties of Suicide Inhibition
1. Irreversible inhibition
2. More effective inhibitor
3. synthesized with the help of enzyme
4. Inhibition of xanthine oxidase by Allopurinol (treatment of GOUT )
5. Alloxanthine synthesized by xanthine oxidase using Allopurinol is more
potent inhibitor of enzyme than Allopurinol
6. Arachidonic acid  Prostaglandin ( cyclo oxygenase )is inhibited by Aspirin
.(anti inflammatory )
7. 5 Fluoro-Uracil  5 Fluoro Deoxy Uridylate more potent inhibitor of
Thymidylate synthase to inhibit nucleotide synthesis and is being used in cancer
treatment

36. Properties of
Suicide
inhibition

37. Suicide Inhibition of Allopurinol

38. Mechanism of action of 5-Fluorouracil

39. Competitive inhibitors-Therapeutic uses
Inhibitor (drug ) Enzyme inhibited Disease treated
Allopurinol Xanthine Oxidase Gout
Epidrene (MAO
INHIBITOR )
Mono Amino Oxidase Psychiatric Treatment
Succinyl CoA Acetyl CoA Anesthesia
Dicumarol VITAMIN K EPIOXIDE REDUCTASE ANTICOAGULANT
Lovastatin HMG CoA reductase Reducing Cholesterol levels
INH ( Isonicotinic acid
hydrazide )
Pyridoxal phosphate Tuberculosis
Neostigmine Acetyl Choline Esterase Myasthenia Gravis
Alpha Methyl Dopa Dopa Carboxylase Myasthenia Gravis

40. Competitive inhibitors-Therapeutic uses
Inhibitor (drug ) Enzyme inhibited Disease treated
Penicillin Trans peptidase bactericidal
Sulphonamide ( analog PABA ) Steroid synthatase Bactericidal
Trimethoprim FH2 reductase bactericidal
Pyri methamine FH2 reductase bactericidal
Methotrexate FH2 reductase Leukemia
6 –Mercapto purine Adenylo Succinate Synthtase Cancer
5 –Fluoro Uracil Thymidylate Synthtase Cancer
Azo Serine Phospho Ribosyl Amido Transferase Cancer
Cytosine Arabinoside DNA Polymerase Cancer
ACYCLOVIR DNA Polymerase Cancer

41. Therapeutic uses
Of enzyme inhibitors