enzyme classification and nomenclature by International Union of Biochemistry and Molecular Biology

1. CLASSIFICATION OF
ENZYMES
MARIA K JOHN
M.Sc. BIOTECHNOLOGY

2. What shall we learn?
What are Enzymes?
Its Nomenclature
Classification
Summary

3. ENZYMES
 Enzymes are biological catalysts, which regulates the rate at which chemical
reactions proceed without itself being altered in the process.
 Frederick W. Kühne gave the name ‘enzymes’ to the molecules detected by
Eduard Buchner.
 Enzymology is the branch of biochemistry aiming to understand how enzymes
work, their kinetics, and structure.
 Central to every biochemical processes.
 Almost all enzymes are proteins, except catalytic RNA molecules(ribozymes).

4. Nomenclature of Enzymes
 Enzymes are commonly named by adding the suffix –ase to the name of their
substrate or to a word describing their activity.
 The scheme for the systematic functional classification and nomenclature of
enzymes was adopted by International Union of Biochemistry and Molecular
Biology (IUBMB).
 Enzymes are classified and named according to the nature of the chemical
reactions they catalyze.
 All enzymes were categorized into SEVEN major classes.
 Based on this classification, a ‘four-digit unique number’ (called EC number) is
assigned to each enzyme as an identification code.

5. Features
 7 major classes.
 Each major class is divided into sub-
classes.
 Each sub-class is further divided into
sub-sub-classes.
 Each enzyme has been assigned a
specific code number, called Enzyme
Commission number (EC number).
 EC number consists of 4 digits,
separated by points.
 For example, EC 2.7.1.1 is Hexokinase.
 Each digit in the EC number implies:
First digit  Major class
Second digit  Sub-class
Third digit  Sub-sub-class
Fourth digit  Systematic specific
name of the enzyme.
 The systematic specific name consists
of two parts:
First part  name of the substrate
Second part  nature of the reaction.

6. CLASSIFICATION

7. Add a Slide Title - 3

8. OXIDOREDUCTASES (EC 1)
Examples: Alcohol dehydrogenase,
Oxidase
Catalyzes oxidation and
reduction reactions(redox
reactions).
This reaction involves the
transfer of protons or electrons
between substrates.

10. TRANSFERASES (EC 2)
Examples: Transaminase, Hexokinase A-B + C  A + B-C
Catalyze the transfer of a
functional group from one
substance to another.
Methyl, ethyl, amino and
phosphate groups are transferred
by this group of enzyme.

11. HYDROLASES (EC 3)
Examples: Lipases, peptidases,
phosphatases
Catalyze the hydrolysis
reaction with water.
Larger molecules are
hydrolyzed into smaller ones.

12. LYASES (EC 4)
Examples: Decarboxylase,
dehydratases, aldolase
Non-hydrolytic reactions
Catalyzes the addition of
groups to double bonds and
formation of double bonds
by the removal of groups.

13. ISOMERASES (EC 5)
Examples: Triose phosphate
isomerases
A-B-C  A-C-B
Catalyze the transfer of
groups within molecules
to yield isomeric forms.
Catalyzes the intra
molecular group transfer.

14. LIGASES (EC 6)
Examples: DNA ligase, Aminoacyl
tRNA synthetases
A + B + ATP  AB + ADP+ Pi
Catalyze the condensation of
two molecules with the
expense of energy from ATP
hydrolysis.
Catalyzes the formation of C-
C, C-S, C-O, and C-N bonds
by the condensation reaction
coupled with ATP cleavage.

15. TRANSLOCASES
Example: ATP synthase
Newly added class of enzyme
classification.
Catalyze the movement of
ions or molecules across
membranes or their
separation within molecules.

16. EC number Enzyme class Reaction type Examples
EC 1 Oxidoreductases Oxidation-reduction reactions Alcohol dehydrogenase (EC 1.1.1.1)
EC 2 Transferases Transfer of functional groups Transaldolase (EC 2.2.1.2),
Transketolase (EC 2.2.1.1)
EC 3 Hydrolases Hydrolysis reactions Cellulase (EC 3.2.1.4)
EC 4 Lyases Group elimination to form double
bonds
Pyruvate decarboxylase (EC 4.1.1.1),
Tryptophan synthase (EC 4.2.1.20)
EC 5 Isomerases Isomerization Triose phosphate isomerase (EC 5.3.1.1),
Alanine racemase (EC 5.1.1.1)
EC 6 Ligases Bond formation coupled with ATP
hydrolysis
Pyruvate carboxylase
(EC 6.4.1.1),DNA ligase(EC 6.5.1.1),
Carbamoyl phosphate synthetase I
( EC 6.3.4.16)
EC 7 Translocases Movement of ions or molecules across
membranes
Cytochrome c oxidase (EC 7.1.1.9)

17. References
 McDonald, A.G., Boyce, S. and Tipton, K.F. ExplorEnz: the primary source of the
IUBMB enzyme list. Nucleic Acids Res. 37, D593–D597 (2009).
[DOI: 10.1093/nar/gkn582]
 http://expasy.org/enzyme
 Nelson, David L. Lehninger Principles Of Biochemistry. New York : W.H.
Freeman, 2008. Print.
 Voet, D., & Voet, J. G. (1995). Fundamentals of Biochemistry. New York: J.
Wiley & Sons.
 Berg, Jeremy M., John L. Tymoczko, Lubert Stryer, and Lubert Stryer.
2002. Biochemistry. New York: W.H. Freeman.