Classification of Enzymes | Microbiology

In this article we will discuss about the classification of enzymes.

The enzymes are classified by the reactions they catalyze by adding the “ase” to the name of their substrate or to a suffix word or phrase which is meant for their activity, e.g., urease which catalyzes the hydrolysis of urea, and DNA polymerase which catalyzes the synthesis of DNA. But some enzymes, e.g., Pepsis and trypsin bear names which do not denote their substrates. Sometimes same enzyme has two or more names or two different enzymes have same name.

To reduce confusion a rational naming and numbering system has been devised by “Enzyme Commission of International Union of Molecular Biology. According to it the enzymes are divided into six major classes with subgroups and sub-subgroups to define their functions in a better and precise manner. Each enzyme is assigned a four digit classification number and a systematic name which identifies the reaction catalyzed, e.g. the formal systematic name of the enzyme which catalyzes the reaction. . ATP + D-glucose →ADP + D-glucose – 6 – Phosphate

Would it be ATP:

Glucose phosphotransferase it catalyzes the transfer of a phosphate group from ATP to glucose. Its enzyme classification number or E.C. number is 2.7.1.1. Here, The first digit 2 denotes the class name transferase, the second digit 7 stands for the subclass phosphotransferase, the third digit 1 strands for phosphotransferases with hydroxyl group as acceptor, and the fourth digit I denotes the D-glucose as a phosphate group acceptor. In case when the systematic name of an enzyme is long or cumbersome, a trivial name may be used, as in case of hexokinase. It is not possible here to go in more detail.

However, the major 6 groups according to international classification of enzymes are:

1. Oxidoreductases:

Catalyze oxidation reduction reactions. They catalyze transfer of electrons (hydride ions or hydronium ion).

2. Transferases:

Catalyze transfer of functional groups from one molecule to another.

3. Hydrolases:

Catalyze hydrolytic cleavage that means catalyze hydrolysis reactions (transfer of functional groups to water)

4. Lyases:

Catalyze removal of a group from or addition of a group to a double bond, or other cleavages involving electron rearrangement.

5. Isomerase:

Catalyze intra molecular rearrangement. Catalyze transfer of groups within molecules to yield isomeric forms. enzymes: biological catalysts or biocatalysts

6 Ligases:

Catalyze reactions in which two molecules are joined, e.g. formation of C -C, C – S, C – O, and C – N bonds by condensation reactions coupled to ATP cleavage.