Enzyme Nomenclature (FBLT)

Trivial Nomenclature

The originally used term ferments, which was based on the fact that enzymes are involved in fermentation, is no longer used. Enzymes discovered among the first were usually named after their source' or the method by which they were discovered. Thus, their names tend to be unrelated to the mechanism of the reaction they catalyze. Many end with the suffix -in - see pepsin found in the digestive juices of the stomach (Greek pepsis - digestion) or ptyalin found in saliva (Greek ptyalon – saliva).

Recommended Terminology

It introduces a system into the nomenclature and is at the same time simpler than systematic nomenclature, which is why we often use it in everyday practice. We create the name by combining:

1. Substrate + -ase (-asa) - for example amylase (catalyzing the hydrolysis of amylose);
2. Type of reaction + -ase - for example dehydrogenase.

Systematic nomenclature

Systematic nomenclature was introduced by IUB (International Union of Biochemistry). Each enzyme has its own EC' (Enzyme Commission) number consisting of four digits - x.x.x.x. The first indicates one of the six main enzyme classes, the other two a subgroup and a subsubgroup. The last one indicates the order of the enzyme in the subgroup (and thus completely characterizes the given enzyme). We recognize these seven major classes of enzymes':

1. oxidoreductases,
2. transferases,
3. hydrolases,
4. lyases (synthases),
5. isomerases,
6. ligases (synthetases),
7. translocases.

Oxidoreductases

Oxidoreductases catalyze reactions in which there is oxidation of one component and reduction of another component. They often use cofactors – e.g. NAD⁺, NADP⁺, FAD or heme. Oxidoreductases include:

• oxidases, peroxidases,
• oxygenases – introduce oxygen into the substrate molecule, either in the form of -OH (monooxygenases or hydroxylases) or as O₂ (dioxygenases),

• dehydrogenases – oxidize the substrate by removing H-atoms, their name is abbreviated as DH (e.g. lactate dehydrogenase – LDH, alcohol dehydrogenase – ADH),

• desaturases.

Transferases

Transferases are involved in the transfer of various groups (amino-, acyl-, methyl-, glycosyl-, phosphoryl-, ...). Examples of transferases are:

• transaminases (aminotransferases) – transfer the -NH₂ group,

• kinases (phosphotransferases) – transfer the phosphate group from ATP or other nucleoside triphosphates,

• transaldolase, transketolase.

Hydrolases

They catalyze hydrolytic reactions (the splitting of bonds in molecules by means of a water molecule). Hydrolases include:

• lipases, phospholipases,

• disaccharidases (sucrase, maltase, lactase),

• proteases, peptidases (pepsin, trypsin),

• esterases,

• phosphatases.

Lyases (synthases)

They catalyze the removal of a certain group from the substrate without hydrolysis (non-hydrolytic cleavage of e.g. bonds between C-C, C-N) as well as addition reactions to double bonds and syntheses without consumption of ATP. Examples of lyases are:

• decarboxylase,

• aldolase,

• dehydratases, hydratases.

Isomerases

They catalyze changes within one substrate molecule (intramolecular changes). The resulting product is an isomer of the starting substrate. Isomerases include:

• epimerase – changes the position of the -OH group in the molecule,

• mutases – change the position of the phosphate group in the molecule.

Ligases (synthetases)

They catalyze synthetic reactions associated with ATP hydrolysis (coupling exergonic and endergonic reactions). Examples of ligases are:

• carboxylase,

• DNA-ligase.

Translocases

They ensure the movement of substances across the biological membrane. They enable a specific transfer of atoms and molecules. E.g.:

• TOM complex - ensures the transition of the outer mitochondrial membrane (translocase of the outer mitochondrial membrane)

• ADP-ATP-translocase – catalyzes the antiport of ATP behind ADP on the inner mitochondrial membrane