How to Name and Classify Your Enzyme

This is a brief guide to the enzyme list and principles of classification.

The enzyme classification system

Each enzyme is assigned a recommended name; usually at the suggestion of the person who submits the details. The rules used to classify enzymes can be found at Each enzyme is allocated a four-digit EC number, the first three digits of which define the reaction catalysed and the fourth of which is a unique identifier (serial number). Each enzyme is also assigned a systematic name that uniquely defines the reaction catalysed.

The recommended names and EC number should be referred to in publications. This has a number of benefits: it will eliminate some of the ambiguities in the literature that have been caused by people using the same name for different enzymes and will also make the searching of literature databases more efficient. The EC number can also be used to find ancillary information, such as genes, sequences, properties and structures in other databases.

An enzyme should be listed IF:

An enzyme is not classified as a new enzyme IF: There are exceptions to these guidelines, for example, among the peptidases and ATPases/GTPases.


An enzyme system, consisting of a number of proteins with different catalytic activities is named a system (e.g. fatty acid synthase system). The overall reaction is not normally given an EC number but each individual enzyme is given a number, and its involvement in the system is described in the comments.

To obtain a listing for a previously unlisted enzyme:

The procedure for recommending a new enzyme for inclusion in the enzyme database is straightforward. Complete the form available at, which will be sent to Prof K.F. Tipton ( and Dr Sinéad Boyce (, of Trinity College Dublin. They are responsible for assignment of EC numbers and maintenance of the enzyme list for the nomenclature committee of IUBMB. Enzymes that have been approved are displayed on the enzyme website at and those awaiting approval can be reviewed at

Information you are requested to provide:

Then what happens:

Amendments to existing entries:

You can also provide information about errors/updates to existing enzyme entries by completing the form available at If an error necessitates changing the classification of an enzyme, i.e., its EC number, then the old entry will be marked as having been deleted or transferred and a link will be provided to the new entry.

Use of EC numbers

Enzyme entries, including EC numbers, may be quoted in any publication without permission. The copyright of the enzyme list rests with the IUBMB.

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