In this ppt competitive inhibition of enzymes is fully explained with its examples. it will be helpful for all the life science students. Non Competitive inhibition , Uncompetitive inhibition & Irreversible inhibition of Enzymes have been well explained in this presentation. it will be helpful for biochemistry, botany, zoology and other life/bio sciences students. I tried to explain Allosteric enzymes, their mechanism of action, Allosteric inhibition, Feedback inhibition in this presentation so that it can be easy to understand the concept for viewers.

1. Enzyme
inhibition
BY: Dr. Sunita Sangwan
Assistant Prof. Dept of Botany,
Govt. college Bhiwani, Haryana

2. • Catalytic activity of the enzymes is inhibited or
decreased by certain compounds. These compounds
are known as inhibitors.
• It can prevent formation of Enzyme-Substrate
complex or can prevent ES breakdown to enzyme +
product.
• These decrease the rate of reactions.
Enzyme Inhibition

4. • Inhibitor binds to the enzyme with weak interaction
(Non- Covalently) so can be dissociates from the
enzyme.
• When inhibitor is removed enzyme action is fully
restored and increase the rate of reaction, so it is
reversible.
Reversible Inhibition

5. • This is also known as substrate analogue inhibition.
• Inhibitor has close structural resemblance with substrate.
• Inhibitor (I) binds to the substrate site of enzyme forming
enzyme-inhibitor (EI) complex.
• Due to competition between substrate and inhibitor, this
type of inhibition is known as competitive inhibition.
• Both ES and EI complexes are formed but only ES can form
the product
1. Competitive Inhibition

8. • The relative amounts of ES and EI complexes depend upon the
relative concentrations of the substrate and the inhibitor.
• If the inhibitor concentration is higher, more EI complex will be
formed resulting in decreased formation of the product.
• If the substrate concentration is higher, more ES complex will be
formed, and the inhibition will be Less.
• So this inhibition can be reversed by increasing concentration of
substrate.
• So degree of inhibition depends on
concentration of substrate (S) and inhibitors (I)
Affinity of enzyme for S & I

9. • Competitive inhibitors do not affect the Vmax but more
substrate is required to reach the Vmax in the presence of
the inhibitor.
• Competitive inhibitors increase the the Km of reaction.
• The inhibitors that raise the Km to a higher degree are
more effective inhibitors
• Examples of competitive inhibitors: Malonate, Sulpha
drugs

10. • Malonate is competitive inhibitors of enzyme
succinate dehydrogenase.

11. • Sulpha drug is antibacterial
as it stops the synthesis of
folic acid which is necessary
for the synthesis of RNA
and DNA.
• They are competetive
inhibitors of this reaction as
they are structural analog
of the PABA ( para amino
benzoic acid).

13. • The non-competitive inhibitors have no structural
resemblance with the substrate.
• They do not compete with the substrate for the substrate
site on the enzyme hence named Non- Competitive
inhibition.
• They bind to some other region of the enzyme and make
it inactive so formation of both EI and EIS is possible.
• EIS forms products at slower rate than ES.
• So reaction is slow not stopped.
2. Non-Competitive Inhibition

15. • Km – unchanged as inhibitor does not interfere with the binding of substrate to
the enzyme.
• Vmax- decreased as inhibition can not be overcomed by increasing the
substrate concentration.
• Non-competitive inhibition may be reversible or irreversible. Generally it is
irreversible
• This means that non-competitive inhibitors lower the Vmax but do not affect the
Km
• Examples of Non- competitive inhibition:
 Cyanide and H2S inhibit the iron containing enzymes such as peroxidases,
catalase etc.
 Heavy metals inhibits the certain enzyme having sulphydryl group (Ex. Urease).
Non-Competitive Inhibition

16. • Antidote for Heavy metal (lead/Arsenic/mercury)
poisoning is an example of non- competitive inhibition.
• In treatment of lead/arsenic/mercury poisoning
advantage is taken of the affinity of heavy metals to the –
SH group. Therefore sulphahydryl (Eg. Dimercaprol/BAL
{British anti lewisite}) compounds are administered to
interact with the metal in the circulatory system and
forms mercaptides, which are then excreted.

17. • Inhibitor binds to the ES complex not to the E alone.
• Inhibitor can cause structural distortion to the enzyme
active site and make the enzyme catalytically inactive.
• In such case both Vmax and Km decreases.
• Example: Inhibition of placental alkaline phosphatase by
phenyalanine.
3. Uncompetitive Inhibition

19. Summary of reversible enzyme inhibition

20. • The binding of an inhibitor can stop a substrate from entering the
enzyme's active site from catalyzing its reaction.
• Inhibitor binds at or near the active site of the enzyme irreversibly,
usually by covalent bonds, so it can’t dissociate from the enzyme.
• Irreversible inhibitors combine with the functional groups of the
amino acids in the active site, irreversibly.
• Irreversible inhibitors occupy or destroy the active sites of the
enzyme permanently and decrease the reaction rate.
• Enzyme activity is not regained
Irreversible Inhibition

21. • Active site directed inhibitor is also called as affinity
label. It is a chemically reactive compound that is
designed to resemble the substrate of an enzyme so
that it binds at the active site and forms a stable
covalent bond with a susceptible group of the nearby
residue in the enzyme protein.
1. Active site directed inhibitor

22. • A suicide inhibitor is a relatively inert molecule that is
transformed by an enzyme at its active site into a reactive
compound that irreversibly inactivates the enzyme.
• They are substrate analogs designed so that via normal
catalytic action of the enzyme, a very reactive group is
generated.
• The latter forms a covalent bond with a nearby functional
group within the active site of the enzyme causing irreversible
inhibition.
2. Suicide inhibitor

23. • Allosteric means other site
• These enzymes have two receptor sites
• One site fit the substrate called catalytic or active site
• The other site is for inhibitor or activator is known as Allosteric site.
• A metabolite which upon binding to the allosteric site alters the kinetics of
enzyme is known as Modulator or effectors.
• Two types of allosteric enzyme based on the modulator:
1. Homotropic: substrate and modulator are same. Ex- Hemoglobin
2. Heterotropic: when modulator has structure different from substrate
Allosteric Enzyme

25. Mechanism of Kinetic behavior of allosteric
enzyme
Concerted/Symmetry
model
Sequential/Induced
fit model

26. • Given by Jacques Monod, Wymanand
Changeux in 1965.
• Equilibrium between T & R states
• Transition is a concerted process, affecting
all subunits simultaneously in the same
way.
• In absence of ligand or substrate
equilibrium favors T state
• Ligand/substrate binding shifts the
equilibrium to R state
• Only models positive co-operativity .
Concerted/ Symmetry model
T- tense form has low affinity for
substrate
R- relaxed form, has high affinity for

27. • Given by Koshland, nemethy, Filmer (KNF) in 1966.
• Ligand binding at one site causes protein conformational
change (induced fit), Shifting binding affinity in adjacent
subunit only, so complete T→R transition is a sequential
process.
• Can account for both positive and negative cooperativity.
Sequential/induced Fit model

28. • When an inhibitor binds to the allosteric site, the
conformation of active /catalytic site is modified so that
substrate cannot bind properly.
Allosteric Inhibition

30. • Feedback inhibition occurs when the biochemical product of a
pathway blocks an enzyme in the begning of the pathway.
• This occurs when there is a build up of product/excess of product
is being produced.
• Cell use this method to slow down the production, coserve
energy and to keep the state of balance within cell.
Feedback Inhibition

33. • https://youtu.be/h8dyPhzo7bw Competitive enzyme inhibition
• https://youtu.be/W8tLzFoJsX4 Non Competitive ,Uncompetitive
& irreversible inhibition
• https://youtu.be/AZ-GaaB7vCg Allosteric enzymes, allosteric
inhibition & feedback inhibition
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