This document discusses the classification of enzymes. It explains that enzymes are classified into six main groups (oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases) based on the type of chemical reaction they catalyze. Each enzyme is also assigned a four digit EC number based on this classification to unambiguously identify the specific reaction it catalyzes. The document provides examples to illustrate each of the six enzyme groups and how they are classified according to the IUB and EC systems.

1. Classification of Enzymes

2. 1.Classification of enzymes with examples:
• In olden days enzymes were named by adding “ase” to the name
of the substrate.
• For E.g. Urease was named based on the substrate it acts on “Urea”.
• Based on International Union of Biochemistry (IUB) convention, each enzyme
is classified into one of six groups depends on the type of chemical reaction
that it catalyses.
• Each group is divided into sub groups according to the nature of the chemical
group and coenzymes involved in the reaction.
• In accordance with Enzyme Commission (EC) each enzyme can be assigned a
four digit number code and unambiguous systemic name based upon the
reaction catalyzed.

3. The six groups are:
1.Oxidoreductase
2.Transferases
3.Hydrolases
4.Lyases
5.Isomerases
6.Ligases

4. CH3-CHO + NADH + H+
CH3-CH2-OH + NAD+
Reduced Oxidized Oxidized Reduced
1.Oxidoreductase:
• Transfer hydrogen or oxygen atoms or electrons from one substrate to
another.
• The group includes the dehydrogenases, reductases, dioxidases,
hydroxylases, peroxidases and catalase.
Recommended name: Alcohol dehydrogenase
Systemic name: Alcohol: NAD+ oxido-reductase
EC number: 1.1.1.1
First digit: oxido-reductase
Second digit: acting on CH-OH group
Third digit: NAD+ as electron acceptor
Fourth digit: the specific enzyme

5. 2. Transferases:
• Transfer chemical groups (methyl, acetyl, mercapto groups
etc) between substrates.
• This includes the kinases, aminotransferases,
acetyltransferases, carbamyltransferases and
phosphorylases.
• The second number indicates the nature of the chemical
group transferred from one substrate to another substrate.
• For E.g. 2.1 indicates transfer of one carbon group (-CH3, -
CH2-, formyl group)
• Third number indicates the type of carrier of the
transferred group or the type of acceptor of the transferred
group.
• The third number depends on the second number also.
• 2.3.1 indicates acetyl CO-A as the carrier group

6. Carbamoyl phosphate + Phosphoric acid +
Aspartic acid N-Carbamoyl aspartic
acid
Recommended name: Aspartate Carbamoyl transferase
Systemic name: Carbamoyl phosphate L-Aspartate carbamoyl transferase
EC number: 2.1.3.2
Glucose + ATP Gluco -6-phosphate + ADP
Recommended name: Gluco kinase
Systemic name: ATP 6 phospho gluco transferase
EC number: 2.7.1.2
Pyruvate + ATP Phosphoenol pyruvate + ADP
Recommended name: Pyruvate kinase
Systemic name: ATP 6 pyruvate phospho transferase
EC number: 2.7.1.40

7. 3. Hydrolases: catalyses the hydrolysis of macromolecules into smaller ones.
E.g. Lipase, Phosphatase, Amylase, Proteases, Peptidases, Maltase, Sucrase etc.
Second number indicates the bond it acts on to hydrolyze.
3.1 indicates ester bond
3.2 indicates glycosyl bond
3.3 indicates ether bond
3.4 indicates peptide bond

8. Third number indicates type of bond in the sub class
3.1.1 indicates carboxylic bond
3.1.2 indicates thiol ester bond
3.1.3 indicates phosphoric mono ester
3.2.1 indicates glucosidic bond
Recommended name: Acetyl choline esterase
Systemic name: Choline acetyl hydrolase
EC number: 3.1.1.8
Acetyl choline + H2O Acetic acid + Choline

9. Recommended name: Glucose 6 posphatase
Systemic name: D-Gluco- 6- phospho hydrolase
EC number: 3.1.3.9
Recommended name: Amylase
Systemic name: -1, 4 glucan-4-glucano hydrolase
EC number: 3.2.1.1
3.4.4.1 indicates pepsin
D-Glucose 6 phosphate D-Glucose + Phosphate
Amylose Dextrin

10. 4. Lyases: catalyses the addition of chemical groups or atoms to double bonds in
the substrate or removal of chemical groups or atoms from the substrate
producing double bonds.
4.1 carbon-carbon lyases
4.2 carbon-oxygen lyases
4.3 carbon-nitrogen lyases
4.4 carbon-sulphur lyases
4.1.1 carboxy-lyases
4.2.1 Hydro lyases
4.3.1 Ammonia lyases

11. Recommended name: Pyruvate decarboxylase
Systemic name: -oxo acid carboxy lyase
EC number: 4.1.1.1
Recommended name: Argino succinate lyase
Systemic name: L-Argino succinate arginine lyase
EC number: 4.3.2.1
L-Argino succinate Fumarate + L-Arginine

12. 5. Isomerases: catalyses the biological isomerization reactions. E.g. Epimerase,
racemase
5.1 racemases and epimerases
5.2 cis-trans isomerases
5.1.1 acting on amino acids and derivatives
5.1.2 acting on hydroxy acids and derivatives
Recommended name: Retinene isomerase
Systemic name: All-trans Retinene 11-cis isomerase
EC number: 5.2.1.3
All trans retinal 11 cis retinal

13. 6. Ligases: catalyses the ligation (joining together) of two molecules coupled with
the cleavage of a high energy compound like ATP or similar tri phosphates.
Second number indicates the type of bond formed
6.1 forming carbon-oxygen bond
6.2 forming carbon-sulphur bond
6.3 forming carbon-nitrogen bond
Third number indicates the nature of products formed

14. 6.1.1 formation of amino acyl tRNA
6.2.1 formation of acid-thiol
Recommended name: Glutamine synthetase
Systemic name: L. glutamate Ammonia ligase
EC number: 6.3.1.2
Glutamic acid + NH3 Glutamine
ATP ADP+Pi