What is the EC number classification of enzymes?

The EC number classification of enzymes was developed in order to establish a rational classification system for identifying and naming enzymes. This classification categorizes enzymes based on the overall reaction they catalyze.

It is important to understand that the EC number classification cannot be used to identify individual enzymes. Instead, it is used to identify classes of enzymes that catalyze similar reactions.

The EC number classification code provides very specific information about the type of reaction, mechanism, substrates, products, and cofactors. This prevents any confusion that could potentially result from using only the common names of enzymes. Here’s what an EC number indicates:

The first digit denotes the general type of reaction catalyzed by the enzyme. This first digit may range anywhere from one to six.

The second and third numbers further define and narrow down details of the reaction. The second number indicates the enzyme’s subclass which generally contains information about the type of compound or group involved. The third number denotes the sub-subclass. They describe the type of reaction with respect to the compound, bond, group, or product involved in the reaction.

The fourth number is a serial identifier. It denotes the serial number of the enzyme in its sub-subclass. It zeroes in on specific metabolites and cofactors involved.

For example, the EC code 3.1.21.4 can be broken down as follows:

The first number ‘3’ indicates a hydrolase.

The second number ‘1’ indicates that it acts on ester bonds.

The third number ‘21’ denotes that it is an endodeoxyribonuclease producing 5′-phosphomonoesters.

The fourth number ‘4’ indicates that it is a Type II site-specific deoxyribonuclease.