• Enzyme catalysis is the process by which there is an increase in the rate of a reaction through a biological molecule called an enzyme. • For a reaction to be successful, the molecules of the reactants should contain sufficient energy to cross the energy barrier, i.e., the activation energy.

1. Principle &
Mechanism of
Enzyme
Catalysis

2. Enzyme
Catalysis
• Enzyme catalysis is the process by which there is
an increase in the rate of a reaction through a
biological molecule called an enzyme.
• Enzymes are a type of biocatalyst used to modify
the rates of reactions in plants and animals.
• Catalysis by enzymes in a cell is vital because
most biochemical reactions have meager rates of
reactions when uncatalyzed.
• For a reaction to be successful, the molecules of
the reactants should contain sufficient energy to
cross the energy barrier, i.e., the activation energy.
2

3. • While molecules do possess varying amounts of energy, only a few of them have
enough energy higher than the activation energy.
• Enzymes function by decreasing the activation energy by forming an enzyme-substrate
complex.
• An enzyme should be in its native conformation to be biologically active.
• The three dimensional conformation of enzymes have a particular site where the
substrate binds and is acted upon, this site is called the active site.
• The active site is earmarked into two specific areas:
(1) Binding site - where the substrate binds and
(2) Catalytic site - where the enzyme catalysis takes place.
• The amino acids present at the active site are tyrosine, histidine, cysteine, glutamic
acid, aspartic acid, lysine and serine.
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4. 4
• The flexible enzyme changes its shape when the substrate binds to it. This occurs
through a process called induced fit, and the substrate and the enzyme form a
substrate enzyme complex.
• Sometimes enzymes will need a non-protein substance called the cofactor to help
them in the reaction. In these reactions, the protein part of the enzyme (apoenzyme)
binds with the cofactor to form the whole enzyme (holoenzyme).

5.  Highly Efficient - A single molecule of the enzyme catalyst can transform up to a million
molecules of the reactant per second.
 Highly Specific to Reactions - These biochemical catalysts are unique to certain types of
reactions, i.e. the same catalyst cannot be used in more than one reaction.
 Highly effective to Optimum Temperature - The enzyme works at maximum
effectiveness at its optimum temperature, usually 37˚C.The effectiveness declines below
or above the optimum temperature.
 Highly effective to optimum pH - Biochemical catalysis is dependent upon the pH of the
solution. A catalyst works best at an optimum pH which ranges between 5-7 pH values.
 The activity of the enzymes usually increases in the presence of a coenzyme or an
activator such as Na+, Co2+. The rate of the reaction increases due to the presence of a
weak bond which exists between the enzyme and a metal ion.
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Characteristics of Enzyme Catalysis

6. Catalytic
Properties of
Enzymes
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Require in small
concentration
Accelerate rate of
catalysis by
lowering of
activation energy
Don’t alter
properties of end
products
Accelerate
forward or
reverse
reactions to
attain equilibrium
Remain
unchanged at the
end of reaction
Require
hydration for
activity

7. Principle of
Enzyme Catalysis
• Catalysis is the process through which the
rate of a reaction is altered while the
quantity and chemical properties of the
catalyst remain the same.
• The principles of enzyme catalysis are
different but similar in essence to other types
of chemical catalysis.
• The similarity is that the vital factor is the
reduction of energy, which acts as a barrier
between the reactants and products.
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8. • Reducing the activation energy (Ea) increases the number of reactant molecules that
can overcome the barrier and transform into the product.
• One of the most important principles is that enzymes always catalyze reactions in
both directions.
• This is because enzymes can only reduce the energy barriers between products and
reactants. Therefore they catalyze the reactions in both directions.
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FREE ENERGY
• The difference in energy level between the substrate and product is called the change in
Gibbs free energy (G).
• The ∆G indicates whether a reaction is thermodynamically favourable or not.
• The negative value of ∆G indicates that the reaction is energetically favourable.
• If the ∆G is positive it indicates that the reaction is not energetically favourable and
endergonic.
• The ∆G of a reaction is independent of the rate of a reaction while ∆G≠ governs the rate of
reaction.

9. ACTIVATION ENERGY
• The kinetic or collision theory states that for molecules to react they must collide and
must possess sufficient energy to overcome the energy barrier for reaction.
• The minimum amount of free energy required to overcome the energy barrier, so that
substrates transform into the transitional state, is called activation energy or free
energy of activation (∆G≠).
• The transition state is an unstable complex develops at some point in the reaction
between the substrate and the products, and has the highest free energy in the
reaction pathway.
• Activation energy increases kinetic energy of substrates and brings about the
forceful collisions between Enzyme (E) and substrates (S).
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10. Mechanism of
Enzyme
Catalysis
 Enzymes neither initiate the reaction nor
affect the equilibrium ratio of reactants and
products.
 Rather, enzymes accelerate the rate of
reaction 108 to 1012 times in both directions
to attain the equilibrium position.
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11. 11
Theory explaining Mechanism of Enzyme
Catalysis
• The structure or conformation of the
enzyme is rigid.
• The reactant molecule or substrate,
which has the opposite charge to that of
the enzyme, fits in the crevice like a lock
and key.
• Thus the active site of an enzyme is a
rigid and pre-shaped template where
only a specific substrate can bind.
Induced fit model
hypothesis
• The active site is not rigid and pre-shaped.
• The essential features of the substrate
binding site are present at the nascent
active site.
• The interaction of the substrate with the
enzyme induces a fit or a conformation
change in the enzyme, resulting in the
formation of a strong substrate binding site.
• Further, due to induced fit, the appropriate
amino acids of the enzyme are repositioned
to form the active site and bring about the
catalysis.
Lock & key hypothesis

12.  After the substrate and the enzyme combine, mechanisms of catalysis lower the
energy of the transition state.
 This is done by forming an alternate pathway for the reaction.
 There are six different mechanisms of these alternative routes. They are,
SUBSTRATE STRAIN THEORY
• In this model, the substrate is strained due to the induced conformation change in the
enzyme.
• It is also possible that when a substrate binds to the preformed active site, the enzyme
induces a strain to the substrate.
• The strained substrate leads to the formation of product.
• A combination of the induced fit model with the substrate strain is considered to be
operative in the enzymatic action.
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13. Proximity
Catalysis
• This effect theorizes that the proximity
and the orientation of the enzyme-
substrate complex align the reactive
chemical groups and bind them in an
optimal orientation and spatial
relationship for the reaction to be
successful.
• Therefore the rate of reaction
increases due to the proximity and
orientation effect.
• This effect is similar to the effect that
occurs when the concentration of
reagents is increased and thus, the
rate increases.

14. Jens
Martensson
Proton Donors
or Acceptors
• To stabilize the charges that are forming in the
transitions state, the protons donors or acceptors
(acids and bases) may donate or accept protons.
• At the physiological pH, histidine is the most
important amino acid, the protonated form of
which functions as an acid and its corresponding
conjugate as a base.
• The other acids are (OH) group of tyrosine, (SH)
group of cysteine, and amino group of lysine.
• The conjugates of these acids and Carboxyl ions
(COO−) function as bases.
• Ribonuclease which cleaves phosphodiester bonds
in a pyrimidine loci in RNA is a classical example of
the role of acid and base in the catalysis.
Acid - Base
Catalysis

15. 15
Metal - Ion
Catalysis
• This theory states that the metal ion
present in the active site engages in the
catalysis through the coordination of
charge stabilization and shielding.
• Since the metal is positively charged,
only negatively charged ions could be
stabilized.
• Metal ions prove to be advantageous in
enzyme catalysis reactions because pH
does not affect them.

16. Electrostatic Catalysis
• The principle of this is that the
activated complex is stabilized through
the electrostatic attraction between the
enzyme and the substrate.
• This happens because the binding of
the substrate removes water from the
active site and hence decreases the
dielectric constant making it similar to
that of an organic solvent.
• This causes electrostatic interactions
between charged substrates to become
stronger.

17. Covalent Catalysis • This is the process of lowering the energy
of the transition state by covalently
bonding to the side chain or cofactors.
• At a later stage in the reaction, the
covalent bond is broken down to
reproduce the enzymes.
• This process does not lower the activation
energy of the pathway but instead
provides an alternative path.
• The negatively charged (nucleophilic) or
positively charged (electrophilic) group is
present at the active site of the enzyme.
• This group attacks the substrate that
results in the covalent binding of the
substrate to the enzyme.
• In the serine proteases, covalent catalysis
along with acid-base catalysis occur, e.g.
chymotrypsin, trypsin, thrombin etc.
Nucleophilic
Catalysis

18. • Many reactions include two distinct substrates.
• In such cases, the reaction rate may be considerably enhanced by bringing the two
substrates together along a single binding surface on an enzyme.
• NMP kinase bring two nucleotides together to facilitate the transfer of a phosphoryl
group from one nucleotide to the other.
• This strategy takes advantage of binding energy and positions the substrates in the
correct orientation for the reaction to proceed.
• An example of catalysis by approximation - when NMP kinases bring two nucleotides
together to facilitate the transfer of a phosphoryl group from one nucleotide to the
other.
Catalysis by Approximation
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19. CONCLUSIO
N
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 Enzyme catalysis is a complex
process that involves various
mechanisms.
 In actual catalysis of the enzymes,
more than one of processes are
simultaneously operative.
 This will help the substrate to attain a
transition state leading to the formation
of products.
 Enzymes are very efficient and unique
biocatalysts because of their
complexities, diverse conditions that
they thrive in.
 Hence enzymes are not only crucial in
metabolic reactions in the body but
also help in breaking down cellulose
and waste.
 They are also used in detergents,

20. REFERENCES
• https://wp.nyu.edu/biochemistry1_002/wp-
content/uploads/sites/274/2014/10/Biochemistry-1-2014-Lecture-Notes-Chapter-
6.pdf
• https://mysite.science.uottawa.ca/jkeillor/English/Teaching_files/Enzyme%20Cataly
sis.pdf
• https://www.yourarticlelibrary.com/biology/enzyme/enzyme-nomenclature-chemical-
nature-and-mechanism/22734
• https://www.biologydiscussion.com/enzymes/enzymology/enzymology-a-close-
look-with-diagram/11211
• https://byjus.com/jee/catalyst/
• https://en.wikipedia.org/wiki/Enzyme_catalysis
• https://www.slideshare.net/DavidEnoma/enzyme-catalysis-mechanisms-involved