naming and classification of enzyme

1. JESSA S. ARIÑO
BSE-3B
Central Bicol State University of Agriculture

3.  Enzymes are most commonly named by
using a system that attempts to provide
information about the function rather than
the structure of the enzyme.
 Type of reaction catalyzed and substrate
identity are focal points for the
nomenclature.
 A substrate is the reactant in an enzyme-
catalyzed reaction.

4. 1. The suffix –ase identifies a substance as an
enzyme. The suffix –in is still found in the
name of the first enzymes studied such as
trypsin, chymotrypsin, and pepsin.
2. The type of reaction catalyzed by an
enzyme is often noted with a prefix.
 oxidase- catalyzes oxidation
reaction
 hydrolase- catalyzes a hydrolysis
reaction

5. 3. The identity of the substrate is often noted
in addition to the type of reaction.
glucose oxidase- catalyzes oxidation of
glucose
lactate dehydrogenase- catalyzes the
removal of hydrogen from lactate ion.
Infrequently, the substrate but not the
reaction type is given:
Urease- catalyses the hydrolysis of urea
Lactase- catalyses the hydrolysis of lactose

6. According to the International union Of
Biochemistry an enzyme name has two
parts:
-First part is the name of the
substrates for the enzyme.
-Second part is the type of reaction
catalyzed by the enzyme. This part ends
with the suffix “ase”.
Example: Lactate dehydrogenase

7. The International Union of Biochemistry and
Molecular Biology have developed a
nomenclature for enzymes, the EC
numbers; each enzyme is described by a
sequence of four numbers preceded by
"EC". The first number classifies the
enzyme based on its mechanism.

8. Enzymes are classified into six different
groups according to the reaction being
catalyzed. The nomenclature was
determined by the Enzyme Commission in
1961 (with the latest update having
occurred in 1992), hence all enzymes are
assigned an “EC” number. The classification
does not take into account amino acid
sequence (ie, homology), protein structure,
or chemical mechanism.

9.  EC numbers are four digits, for example
a.b.c.d, where “a” is the class, “b” is the
subclass, “c” is the sub-subclass, and “d” is
the sub-sub-subclass. The “b” and “c” digits
describe the reaction, while the “d” digit is
used to distinguish between different
enzymes of the same function based on the
actual substrate in the reaction.
 Example: for Alcohol:NAD+oxidoreductase
EC number is 1.1.1.1

11.  EC 1. Oxidoreductases
 EC 2. Transferases
 EC 3. Hydrolases
 EC 4. Lyases
 EC 5. Isomerases
 EC 6. Ligases
 A list of the subclasses for each class is given below.
Additional information on the sub-subclasses and sub-
sub-subclasses (ie, full enzyme classification and
names) can be found at the referenced web link.
 From the Web version,
http://www.chem.qmul.ac.uk/iubmb/enzyme/index.ht
ml

12.  EC 1. Oxidoreductases :catalyze the
transfer of hydrogen or oxygen atoms or
electrons from one substrate to another,
also called oxidases, dehydrogenases, or
reductases. Note that since these are
‘redox’ reactions, an electron
donor/acceptor is also required to complete
the reaction.

14.  EC 2. Transferases – catalyze group transfer
reactions, excluding oxidoreductases (which
transfer hydrogen or oxygen and are EC 1).
These are of the general form:
 A-X + B ↔ BX + A

16.  EC 3. Hydrolases – catalyze hydrolytic
reactions. Includes lipases, esterases,
nitrilases, peptidases/proteases. These are
of the general form:
 A-X + H2O ↔ X-OH + HA

17. Maltase
Maltose Glucose Glucose

18.  EC 4. Lyases – catalyze non-hydrolytic
(covered in EC 3) removal of functional
groups from substrates, often creating a
double bond in the product; or the reverse
reaction, ie, addition of function groups
across a double bond.
 A-B → A=B + X-Y
X Y
 Includes decarboxylases and aldolases in
the removal direction, and synthases in the
addition direction.

19. Fumarase
Fumarate L-malate

20.  EC 5. Isomerases – catalyzes isomerization
reactions, including racemizations and cis-
tran isomerizations.

21. 3-phosphogycerate 2-phosphogycerate

22.  EC 6. Ligases -- catalyzes the synthesis of
various (mostly C-X) bonds, coupled with
the breakdown of energy-containing
substrates, usually ATP

23. Phosphate
Pyruvate
Oxaloacetate

24. a. Cellulase
b. L- amino acid oxidase
c. Sucrase
d. Maltase
e. Succinate dehydrogenase

25. Group Reaction catalyzed Typical reaction Enzyme example(s) with trivial
name
EC 1 To catalyze oxidation/reduction AH + B → A + BH Dehydrogenase, oxidase
Oxidoreductases reactions; transfer of H and O atoms (reduced)
or electrons from one substance to A + O → AO
another (oxidized)
EC 2 Transfer of a functional group from one AB + C → A + BC Transaminase, kinase
Transferases substance to another. The group may be
methyl-, acyl-, amino- or phosphate
group
EC 3 Formation of two products from a AB + H2O → AOH Lipase, amylase, peptidase
Hydrolases substrate by hydrolysis + BH
EC 4 Non-hydrolytic addition or removal of RCOCOOH → Decarboxylase
Lyases groups from substrates. C-C, C-N, C-O RCOH + CO2 or
or C-S bonds may be cleaved [X-A-B-Y] → [A=B
+ X-Y]
EC 5 Intramolecule rearrangement, AB → BA Isomerase, mutase
Isomerases i.e. isomerization changes within a
single molecule
EC 6 Join together two molecules by X + Y+ ATP → XY Synthetase
Ligases synthesis of new C-O, C-S, C-N or C- + ADP + Pi
C bonds with simultaneous breakdown
of ATP

26. A. CELLULASE catalyzes the hydrolysis
of cellulose
B. L-AMINO ACID OXIDASE catalyses
the oxidation of L-amino acids.
C. SUCRASE catalyses the hydrolysis of
the disaccharide sucrose
D. MALTASE catalyses the hydrolysis of
the disaccharide maltose
E. SUCCINATE DEHYDROGENASE
catalyzes the removal of hydrogen
from succinate ion