Enzymes are biocatalysts synthesized by living cells that accelerate chemical reactions without altering themselves. They are classified into six major categories based on the type of reactions they catalyze, encompassing a wide range of functions specific to various substrates. Enzymes are predominantly proteins, with specific structures essential for their activity, often consisting of an apoenzyme and a coenzyme.

1. Enzymes

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

3. Enzyme
Enzyme may be defined as biocatalysts synthesized by
living cells.
They are protein in nature (except ribozyme), colloidal
and thermo liable in character and specific in their
action

4. Historical background
• Berzelius in 1836 coined the term catalysis (Greek-to dissolve)
• In 1878, Kuhne used the word enzyme (Greek-in yeast) to
indicate the catalysis taking place in the biological systems.
• Isolation of enzyme system from cell free extract of yeast was
achieved in 1883 by Buchner. He named the active principle as
zymase which could convert sugar into alcohol
• In 1926, James Sumner first achieved the isolation and
crystallization of the enzyme urease from lack bean and
identified it as a protein

5. Nomenclature and classification
• In the early days, the enzymes were given names by
their discoverers in an arbitrary manner. For example
the names pepsin, trypsin and chymotrypsin convey
no information about the function of enzyme or the
nature of the substrate on which they act
• Sometimes the suffix ase was added to the substrate
for naming the enzyme. e.g. Lipase acts on lipids,
nuclease on nucleic acid, lactase on lactose

6. • Enzymes are sometimes considered under two broad
categories
Intracellular enzymes
Extracellular enzymes
• The international union of biochemistry (IUB) appointed
an enzyme commission in 1961. enzymes are divided into
six major classes. Each class on its own represents the
general type of reaction brought about by enzymes of the
class

7. 1. Oxidoreductase
2. Transferase
3. Hydrolases
4. Lyases
5. Isomerases
6. Ligases

8. Oxidoreductases
• Enzymes involved in oxidation reduction reactions
e.g. (alcohol: NAD+ oxidoreductase E.C. 1.1.1.1),
cytochrome oxidase, L and D amino acid oxidase
Oxidation reduction
AH2 + B A+BH2

9. Transferases
• Enzymes that catalyze the transfer of functional
groups
• Hexokinase, transaminase, transmethylase,
phosphorylase
Group transfer
A-X + B A+B-X

10. Hydrolases
• Enzymes that bring about hydrolysis of various
compounds
• Lipase, alkaline phosphastases, pepsin, urease
Hydrolysis
A-B +H2O AH +BOH

11. Lyases
• Enzymes specialized in the addition or removal of
water, ammonia CO2 etc
• Aldolase , fumarase, histidase
Addition elimination
A-B + X-Y AX-BY

12. Isomerases
• Enzymes involved in all isomerization reactions
• Triose phosphate isomerase, phosphohexose
isomerase
Interconversion of isomers
A A’

13. Ligases
• Enzymes catalyzing the synthetic reactions where
two molecules are joined together and ATP is used.
• Glutamine synthetase, succinate thiokinase
Condensation
A+B A-B
ATP ADP+ Pi

14. • Each class is in turn subdivided into many subclasses which are
further divided
• A four digit EC number is assigned to each enzyme representing
the
 Class (1st digit)
 Sub-class (2nd digit)
 Sub-sub class (3rd digit)
 Individual enzyme (4th digit)
• Each enzyme is given a specific name indicating the substrate, co-
enzyme (if any ) and the type of reactions catalyzed by the enzyme

15. Chemical nature and properties of
enzymes
• All the enzymes are invariably proteins however few RNA
molecules have been shown to function as enzyme
• Each enzyme has its own tertiary structure and specific
conformation which is very essential for its catalytic
activity
• The functional unit of the enzyme is known as
HOLOENZYME which is often made up of apoenzyme
(the protein part ) and coenzyme (the non-protein part)

16. • The term prosthetic group is used when the non-
protein moiety tightly binds with the apoenzyme
• The term monomeric enzyme is used if it is made up
of single polypeptide e.g. Trypsin
• The enzyme posses more than one polypeptide chain
are known as oligomeric enzymes e.g. lactate
dehydrogenase