An enzyme is a biological catalyst and is almost always a protein. It speeds up the rate of a specific chemical reaction in the cell. The enzyme is not destroyed during the reaction and is used over and over.

1. ENZYMES
By
Mr. Abhijit Bhoyar
Department of Child
Heath Nursing
Biochemistry

2. Specific Learning Objectives
At the end of the lecture, student should be able to:
1. Define enzymes
2. Describe enzymes of diagnostic enzyme
3. Define isoenzymes
4. Explain the properties of isoenzymes

3. Introduction
• Enzymes are biocatalysts- the catalysts of life.
• A catalyst is defined as substance that increases
velocity or rate of a chemical reaction without itself
undergoing any change in the overall process.

4. Definition
• Enzymes is defined as biocatalysts synthesized by
living cells. They are protein in nature (exception –
RNA acting as ribozyme), colloidal and thermo-labile
in character, and specific in their action

5. Enzymes
• Enzymes are biological catalysts produced by living
tissues.
• They increase the rate of chemical reactions in
biological and in vitro systems.
• Zymogen or Proenzyme: precursor (inactive form
of an enzyme e.g. chymotrypsinogen –
chymotrypsin
• Cofactors (Coenzyme and Activator): Some
Enzymes require additional non-protein component
for its optimum activity.

6. MECHANISM OF ACTION
Free energy of activation:
• The energy difference between the energy of reactant
and high energy intermediates that occur during the
formation of a product.
• An enzyme lowers the energy required for activation
of transition state.
• Without catalyst the reaction will occur at high energy
• With enzyme, the reaction may easily proceed at
normal physiological temperature.

7. 1. All enzymes are proteins
2. They accelerate the reaction but –
i. Do not alter the reaction equilibrium
ii. Not consumed in overall reaction
iii. Required only in very small quantities
3. Have enormous power for catalysis
4. Are highly specific for their substrates

8. 5. Posses active sites at which interaction with substrate
takes place.
6. Lower activation energy
7. Form enzyme-substrate (E+S) complexes as
intermediates
8.Some have regulatory function

9. HOW ENZYME WORKS ?

10. Classification
(a) Intracellular enzymes
-They are functional within
cells where they are
synthesized.
(b) Extracellular enzymes
- These enzymes are
active outside the cell; all
the digestive enzymes
belong to this group.
Enzymes are sometimes considered under two broad
categories :

12. Classification of Enzymes
• According to IUB (International Union of
Biochemistry
• Enzyme Code (EC) number is allotted
• Six major classes
1. EC-1 : Oxidoreductases – e.g LDH ,
Chromosome oxidase
2. EC-2 : Transferases – e.g. AST, ALT, Hexokinase
3. EC-3 : Hydrolases – e.g. Lipase, Trypsin,
sucrase, pepsin
4. EC-4 : Lyases – e.g. Aldolase, arginosuccinase
5. EC-5 : Isomerases – e.g. Triphosphate
isomerase, Phosphohexose, isomerase
6. EC-6 : Ligases – e.g. Glutamine synthetase, DNA
ligases, Pyruvate caboxylase

13. Classification of enzymes
• EC-1 : Oxidoreductases – catalyze oxidation – reduction
reactions
• Include
• Dehydrogenases
• Reductases
• Oxidases
• Peroxidases
• EC-2 : Transferases – catalyze the transfer of a group such
as amino, carboxyl, methyl, phosphoryl, etc. From one
molecule to another
• Include
• Amino transferase or transaminase
• Kinase
• Transcarboxylase

14. Classification of enzymes
• EC-3 : Hydrolases – catalyze cleavage of C-C, C-N,
C-O and some other bonds with addition of water.
• Include
• Acid phosphatase
• All digestive enzymes – alpha amylase, pepsin,
trypsin, chymotrypsin, etc.
• EC-4 : Lyases – catalyze cleavage of C-C, C-N, C-O
bonds by means of other than hydrolysis or oxidation
• Give rise to compounds with double bonds
• Or catalyze the reverse reaction by addition of group
to a double bond
• Include
• aldolase

15. Classification of enzymes
• EC-5 : Isomerases – catalyze intramolecular structural
rearrangement in a molecule
• Include
• Epimerases
• Isomerases
• Mutases
• EC-6 : Ligases (Synthetases) – catalyze the joining of
two molecules coupled with hydrolysis of ATP
• Include
• Glutamine Synthetase
• DNA ligase

16. Specificity of Enzyme Action
• Refers to ability of enzymes to discriminate
between two competing substrates.
• Types of Enzyme specificity
Substrate
specificity
Reaction
specificity
Stereo
specificity

18. Substrate Specificity
• Discriminates the specific substrate for action
• Acts only on specific substrates
• Types of Substrate specificity
1. Absolute Substrate specificity – act only on one
substrate and catalyze only one reaction – e.g.
lactase, urease
2. Relative substrate specificity - act on structurally
related substances
3. Broad substrate specificity-act on closely related
substances

20. Reaction Specificity
• An enzyme is specific to a particular reaction but not to
substrate(s) and catalyzes only one type of reaction.
E.g.
• Pyruvate undergoes several reactions.
• Each reaction is catalyzed by a separate enzyme
• which catalyzes only that reaction and none other

21. Stereo Specificity
• Many enzymes show specificity towards stereo-
isomers
• They act on only one type of isomer
• E.g.
• L-Lactate dehydrogenase will act only on L-Lactic
acid and not D-Lactic acid.
• Isomerase and epimerase do not show
sterospecificity

22. Substrate concentration
Enzyme concentration
pH i.e. H+ ion concentration
Temperature
Product concentration
Activators and coenzymes
Time
Physical agents
Inhibitors
Factors Affecting
Enzyme Action

23. • Substrate concentration
• The velocity of the
reaction increases as the
concentration of
substrate is increased
for given quantity of
enzyme.
• Initially the relationship is
linear but later the
reaction curve is
hyperbolic in shape
• Enzyme concentration
• The velocity of the
reaction is directly
proportional to the
amount of enzyme
present as long as the
amount of substrate is
not limiting
• Substrate must be
present at a
concentration sufficient
to ensure that all the
enzyme molecules have
substrate bound to their
active sites.

24. • Effect of H+ ion
concentration
• Each enzyme has optimum
pH i.e. a pH at which the
enzyme activity is
maximum
• Optimum pH differs from
enzyme to enzyme
• Changes in pH alters
ionization state of AA
residues present in the
active site of the enzyme
• Ionization state of substrate
• Drastic change in pH
denatures the enzyme
protein
• Effect of Temperature
• Increased rate of reaction
with increasing temperature
• Optimum temperature for
each enzyme
• Activity declines above or
below this temp.

25. • Effect of Product- Accumulation of product causes
inhibition of enzyme activity
• Effect of Activators & Co-enzymes- Many enzymes’
activity is dependent on the activators like Mg, Mn, Zn,
Ca, etc.
• Absence of these make the enzymes inactive
• Effect of Time- Under optimum conditions of pH and
temperature, time required for an enzyme reaction is less
• Effect of Physical agents- Light rays can inhibit or
accelerate certain enzyme reactions
• Effect of inhibitors- Substance which stop the enzymatic
reactions - inhibitors

26. Summary
• enzymes and coenzymes
• Mechanism of action of enzymes
• characteristic of enzyme
• Classification of enzyme
• factors influencing enzyme activity

27. Expected Question
• Essay / Situational Question
• Describe enzymes with reference to definition and
classification, chemical nature and factors affecting
enzyme activity
• Short Question
1. Explain characteristic of enzyme
2. Describe Classification of enzyme
3. Describe factors influencing enzyme activity

28. THANK YOU