Enzyme Nomenclature

EC 2 Introduction

EC 2 Transferases

Transferases are enzymes transferring a group, for example, the methyl group or a glycosyl group, from one compound (generally regarded as donor) to another compound (generally regarded as acceptor). The classification is based on the scheme 'donor:acceptor grouptransferase'. The Accepted names are normally formed as 'acceptor grouptransferase' or 'donor grouptransferase'. In many cases, the donor is a cofactor (coenzyme), carrying the group to be transferred. The aminotransferases constitute a special case (subclass EC 2.6).

EC 2.1 Transferring One-Carbon Groups

This subclass contains the methyltransferases (EC 2.1.1), the hydroxymethyl-, formyl- and related transferases (EC 2.1.2), the carboxy- and carbamoyl-transferases (EC 2.1.3), and the amidino-transferases (EC 2.1.4).

EC 2.2 Transferring Aldehyde or Ketone Groups

This single sub-subclass (EC 2.2.1) contains transketolases and transaldolases.

EC 2.3 Acyltransferases

These enzymes transfer acyl groups, forming either esters or amides. The donor is in most cases the corresponding acyl-coenzyme A derivative (EC 2.3.1). Aminoacyltransferases form a separate sub-subclass (EC 2.3.2). Acyl groups converted into alkyl on transfer form sub-subclass (EC 2.3.3.

EC 2.4 Glycosyltransferases

To this class belong all enzymes transferring glycosyl groups. Some of these enzymes also catalyse hydrolysis, which can be regarded as transfer of a glycosyl group from the donor to water. Also, inorganic phosphate can act as acceptor in the case of phosphorylases; phosphorolysis of glycogen is regarded as transfer of one sugar residue from glycogen to phosphate. However, the more general case is the transfer of a sugar from oligosaccharide or a high-energy compound to another carbohydrate molecule as acceptor. The subclass is further subdivided, according to the nature of the sugar residue being transferred, into hexosyltransferases (EC 2.4.1), pentosyltransferases (EC 2.4.2) and those transferring other glycosyl groups (EC 2.4.99)

EC 2.5 Transferring alkyl or aryl groups, other than methyl groups

This is a somewhat heterogeneous class of enzymes transferring alkyl or related groups either substituted or unsubstituted. There is no subdivision as yet in this subclass.

EC 2.6 Transferring nitrogenous groups

These are mainly the enzymes transferring amino groups (sub-subclass EC 2.6.1) from a donor, generally an amino acid, to an acceptor, generally a 2-oxo acid. It should be kept in mind that transamination by this reaction also involves an oxidoreduction; the donor is oxidized to a ketone, while the acceptor is reduced. Nevertheless, since the transfer of the amino group is the most prominent feature of this reaction, these enzymes have been classified as aminotransferases rather than oxidoreductases (transaminating). Most of these enzymes are pyridoxal-phosphate proteins.

EC 2.7 Transferring phosphorus-containing groups

This is a rather large group of enzymes comprising not only those transferring phosphate but also diphosphate, nucleotidyl residues and others. The most numerous section, that of phosphotransferases, is subdivided according to the acceptor group which may be an alcohol group (EC 2.7.1), a carboxy group (EC 2.7.2), a nitrogenous group such as that of creatine (EC 2.7.3), or a phosphate group as in the case of adenylate kinase (EC 2.7.4). The diphosphotransferases are in sub-subclass EC 2.7.6, the nucleotidyltransferases in EC 2.7.7, and those with other substituted phosphate groups in EC 2.7.8. With the enzymes of sub-subclass EC 2.7.9, two phosphate groups are transferred from a donor such as ATP to two different acceptors. The protein kinases are divided into the sub-subclasses protein-tyrosine kinases EC 2.7.10, protein-serine/threonine kinases EC 2.7.11, dual-specificity kinases EC 2.7.12, protein-histidine kinases EC 2.7.13 and other protein kinases EC 2.7.99.

EC 2.8 Transferring sulfur-containing groups

These are enzymes transferring sulfur atoms (EC 2.8.1), sulfate groups (EC 2.8.2) or coenzyme A (EC 2.8.3).

EC 2.9 Transferring Selenium-Containing Groups

Represented by a single enzyme which transfers a selenium containing group.

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