Revision of the Enzyme List

The EC list is revised and updated on an ongoing basis, under the direction of K.F. Tipton and S. Boyce. The number of enzymes on the list at present is 3702, as follows:

EC1 Oxidoreductases1011
EC2 Transferases1057
EC3 Hydrolases1041
EC4 Lyases312
EC5 Isomerases152
EC6 Ligases129
A total of 4380 enzymes have been included in the list at various times, of which 539 have been deleted. The full history of changes in the listing of enzymes is included. Two reviews describing the origins and operation of the list have been published [2,3].

Diagrams and metabolic schemes

On the initiative of G.P. Moss and H.B.F. Dixon, the web version of the Enzyme List has been enhanced by the addition, to selected enzyme entries, of

An up-to-date list of reaction schemes is available at

Approval and incorporation of New Enzymes

A new procedure has been implemented that includes a public-review process before enzymes are added to the Enzyme List. The URL is used to display all new/amended enzymes undergoing public review. Comments are invited, to be sent by a specified date, after which the enzyme entries are made official and are added to the Enzyme List.

New subclasses and sub-subclasses

New subclasses have been introduced, to accommodate new enzymes that did not fit into the existing classification as follows:

EC 1.14.20With 2-oxoglutarate as one donor, and the other dehydrogenated
EC 1.14.21With NADH or NADPH as one donor, and the other dehydrogenated
EC 1.20Acting on phosphorus or arsenic in donors
EC 1.20.4With disulfide as acceptor
EC 1.20.98With other, known acceptors
EC 1.20.99With other acceptors
EC 1.21Acting on X-H and Y-H to form an X-Y bond
EC 1.21.3With oxygen as acceptor
EC 1.21.99With other acceptors

Subsubclass EC x.y.99 is, in most cases, reserved for enzymes with unknown or non-physiological acceptors. As knowledge of about these enzymes expandsincreases, the "99" enzymes will be transferred to other subclasses. However, there are cases where the enzyme does not belong in any existing subclasses but the acceptor is known. To denote this fact, these enzymes have been transferred to new sub-subclasses, namely EC x.y.98.

An alternative to the term "Recommended name"

For each enzyme in the Enzyme List, the entry provides two names. The systematic name describes the chemical reaction catalysed, but is often too lengthy for general use. The second name, by which the enzyme is normally described, has been variously called the "Recommended name" or, in the the 1992 printed version of the list [4], it was not given any name. In the case of the peptidases (subclass EC 3.4), the name given is indeed the recommended name, whereas, for other enzymes, these names are merely accepted as being in common use. It has been decided to designate this as the "Common name". The "other names" by which enzymes are described in the literature are also listed.

ATPases and GTPases

These are complex enzymes that have many important cellular functions but their chemical reactions are very similar. As a result, very few were classified in the Enzyme List. In order to accommodate them in the Enzyme List, two new sub-subclasses were created, EC 3.6.3 (Acting on acid anhydrides; catalysing transmembrane movement of substances) and EC 3.6.4 (Acting on acid anhydrides; involved in cellular and subcellular movement). The entries were drafted by A. Kotyk. These can be seen at, and in the Enzyme List.


2. Enzyme Classification and Nomenclature. Tipton K.F. and Boyce, S. (2000) Encyclopedia of Life Sciences Macmillan Reference Co. UK. (

3. History of the Enzyme Nomenclature System. Boyce S. and Tipton, K.F. Bioinformatics 16 (2000) 34-40.

4. Enzyme Nomenclature 1992 edited Webb, E.C. (1992) Academic Press, San Diego.

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