Transferases are a class of enzymes that transfer specific functional groups from one molecule (donor) to another (acceptor). Transferases are implicated in hundreds of different biochemical pathways, and are essential to some of most important processes in lives. Transferases participate in a myriad of cell reactions and are also utilized during translation. Mechanistically, an enzyme catalyzing the following reaction would be considered as a transferase:
Figure 1. Redox reaction.
where X is the donor that is often a coenzyme, and Y is the acceptor. Group would be the functional group that is transferred on account of transferase activity.
Systematic names of transferases are based on the form of “donor:acceptor grouptransferase.” For example, methylamine:L-glutamate N-methyltransferase is the normative name for the transferase methylamine-glutamate N-methyltransferase, where methyltransferase is the EC category, methylamine is the donor, and L-glutamate is the acceptor. Nonetheless, the more frequently used nomenclature for transferases are often in a form of “acceptor grouptransferase” or “donor grouptransferase.” Practically, many molecules are not mentioned by taking advantage of this terminology because of the application of more prevalent common names.
It occurs as early as the 1930s that some of the most important transferases were discovered. Transamination that means the transfer of a NH2 group from an amino acid to a keto acid through an aminotransferase is noticed for the first time in 1930 after the disappearance of glutamic acid appended to pigeon breast muscle, which is subsequently confirmed by the discovery of its reaction mechanism in 1937. This reversible reaction could be also applied to other tissues, which lays the basis for the possibility that their similar transfers act as a main choice of producing amino acids via amino transfer. Later in 1953, enzyme UDP-glucose pyrophosphorylase is revealed to be a transferase, since it is found to be capable of reversibly generating UTP and G1P from UDP-glucose and an organic pyrophosphate. Another historically significant discovery in transferase is illumination of the breakdown mechanism of catecholamine by catechol-O-methyltransferase, which accounts a large part for Julius Axelrod’s 1970 Nobel Prize in Physiology or Medicine.
Up to now, the classification of transferases is still under way for new ones discovered frequently. The category of transferases is described primarily according to the type of biochemical group transferred, and can be divided into ten groups based on the EC Number classification, which comprises more than 450 different unique enzymes and have been assigned a number of EC 2 in the EC numbering system. Hydrogen is not recognized as a functional group when it refers to transferase targets. On the contrary, hydrogen transfer is divided into oxidoreductases in consideration of electron transfer.
|EC 2.1||Single carbon transferases under EC 2.1 are enzymes that transfer single-carbon groups, which contain functional groups of hydroxymethyl, methyl, carboxy, carbamoyl, formyl, and amido substituents.|
|EC 2.2||EC 2.2 includes aldehyde and ketone transferases transferring aldehyde or ketone groups, mainly comprising a variety of transketolases and transaldolases that play important role in pentose phosphate pathway and catalyze the transfer of dihydroxyacetone functional group to glyceraldehyde 3-phosphate.|
|EC 2.3||Acyl transferases as key aspects of EC 2.3 could transfer acyl groups or acyl groups that are converted into alkyl groups during the process of being transferred. Furthermore, this category also distinguishes amino-acyl from non-amino-acyl groups.|
|EC 2.4||Enzymes divided into EC 2.4 could transfer glycosyl, hexosyl and pentosyl groups. Glycosyltransferase under the subcategory of EC 2.4 takes participate in the biosynthesis of disaccharides and polysaccharides by transferring monosaccharides to other molecules.|
|EC 2.5||Currently, EC 2.5 only possesses enzymes that are involved to transferring alkyl or aryl groups, which yet do not include methyl group. This is different from functional groups that are transformed into alkyl groups when transferred.|
|EC 2.6||EC 2.6 is a group of enzymes that are consistent with transfer of nitrogenous groups, including transaminase, oximinotransferases and other nitrogen group transferring enzymes. Amidinotransferase is previously grouped into EC 2.6, while it has recently been reclassified as a subcategory of EC 2.1.|
|EC 2.7||EC 2.7 consists of not only enzymes that transfer phosphorus-containing groups, but also nuclotidyl transferases. Subcategory of phosphotransferase is further divided in accordance with the type of group experiencing the transfer. Phosphate acceptors mainly include alcohols, carboxy groups, nitrogenous groups, and phosphate groups. Various kinases are also constituents of this subclass of transferases.|
|EC 2.8||Sulfur transferases transferring sulfur-containing groups are covered by EC 2.8 and are further subdivided into the subcategories of sulfurtransferases, sulfotransferases, and CoA-transferases, as well as alkylthio groups transferring enzymes. Some specific sulfotransferases could employ PAPS as a sulfate group donor, within which alcohol sulfotransferase has a broad targeting capacity. Therefore, alcohol sulfotransferase is also acknowledged as “steroid sulfokinase,” “hydroxysteroid sulfotransferase,” and “estrogen sulfotransferase.” Decrease in the activity has been concerned with human liver disease.|
|EC 2.9||Selenium transferases belong to EC 2.9 and only contain two transferases, which therefore is one of the smallest categories of transferase.|
|EC 2.10||The class of EC 2.10 covers enzymes transferring molybdenum or tungsten-containing groups. However, only one enzyme molybdopterin molybdotransferase, a component of MoCo biosynthesis in Escherichia coli, has been added until 2011.|
Applications in Biotechnology
Terminal transferase is one of the few DNA polymerases functioning without an RNA primer, and could label DNA or produce plasmid vectors by adding deoxynucleotides in the form of a template to the downstream end or 3′ end of an existing DNA molecule.
Glutathione transferases with high diversity can be applied by plants to segregate toxic metals from the rest of the cell, which thus can be processed as biosensors to detect contaminants such as herbicides and insecticides. Glutathione transferases could also increase resistance to both biotic and abiotic stress in transgenic plants, and now they are being explored as targets for anti-cancer medications owing to their functionality in drug resistance. Currently the only available commercial source of natural rubber is the Hevea plant.