How are Enzymes Named

An enzyme is a protein molecule that can act as a biological catalyst. Enzymes possess three characteristic features. First, the primary function of an enzyme is to increase the rate of a reaction. Second, one particular enzyme acts specifically on one particular substrate, producing a product. And third, enzymes can be regulated by a low activity to high activity and vice versa. Some enzymes are capable of catalyzing the same reaction. They are called isozymes. A unique set of about 3, 000 enzymes are genetically programmed to be synthesized, providing individuality to a cell. If one enzyme becomes defective, the effect would be disastrous. Common names, as well as systematic names, are used in the naming of enzymes.

This article explains,

1. How are Enzymes Named
2. Naming Principles of Enzymes
3. Levels of Classification of Enzymes

The common names of enzymes generally contain a prefix either describing the name of the substrate the enzymes effect or the chemical reaction that they catalyze. The prefix is followed by the suffix ‘ase’. This suffix simply denotes the identification that the compound is an enzyme. For example, the enzyme that breaks down proteins into amino acids is named as ‘proteinase’ or ‘protease’. Likewise, the enzyme involved in the dehydration of alcohols is named ‘alcohol dehydrogenase’. However, when naming some of the originally studied enzymes like rennin, pepsin, and trypsin, older trivial names are used. The enzyme glucosidase is shown in figure 1. It catalyzes the conversion of maltose into two glucose molecules.

Figure 1: Glucosidase enzyme

The systematic nomenclature and the classification of enzymes by the reaction they catalyze are developed by the International Union of Biochemistry and Molecular Biology (IUBMB). Both nomenclature and classification of enzymes deal together due to their close interdependence.

Naming Principles of Enzymes

The three general principles in enzymes nomenclature are,

1. The suffix -ase should only be used for single catalytic entities. Hence, it cannot be applied to systems containing more than one enzyme.
2. The principle classification and nomenclature should be based on the reaction of which a particular enzyme catalyzes.
3. The enzymes are divided into groups, depending on the reactions catalyzed.

The functionally related groups of enzymes are classified by assigning code numbers to each group. The code numbers are prefixed by ‘EC’ along with four elements that are separated by points. The four elements contain following meanings:

The first figure indicates the class of enzyme.
The second figure indicates the subclass of the enzyme.
The fourth figure indicates the sub-subclass of the enzyme.
The fifth figure indicates the serial number of the enzyme in its sub-subclass.

Classification of Enzymes

The top-level of enzyme classification, their names and functions are shown in the below table.

Enzyme Classes	Name and Function
EC 1	Oxidoreductases: Addition or removal of water
EC 2	Transferases: Transfer of electrons
EC 3	Hydrolases: Transfer of radical
EC 4	Lyases: Splitting or forming a C-C bond
EC 5	Isomerases: Changing geometry or structure of a molecule
EC 6	Ligases: Joining of two molecules through hydrolysis of a phosphate bond in ATP or another triphosphate.

Table 1: The top-level of enzyme classification

An enzyme can be fully specified by this nomenclature. For example, hexokinase is a transferase (EC 2), adding a phosphate group (EC 2.7) to hexose sugars that contain an alcohol group (EC 2.7.1). Hence, the nomenclature of hexokinase is EC 2.7.1.1.

Conclusion

Enzymes increase the rate of reactions by catalyzing them. They are commonly named based on the substrate that they act upon. Enzymes are also named based on the type of reaction they catalyze. A systematic nomenclature, combining with the enzyme classification is developed by IUBMB. Enzymes are developed into six classes by the systematic enzyme nomenclature.

Reference:
1. “Enzyme Nomenclature.” IUBMB Biochemical Nomenclature. N.p., n.d. Web. 20 May 2017. <http://www.chem.qmul.ac.uk/iubmb/enzyme/>.
2. “Classification and Nomenclature of Enzymes by the Reactions they Catalyse.” Enzyme Classification. N.p., n.d. Web. 20 May 2017. <http://www.chem.qmul.ac.uk/iubmb/enzyme/rules.html>.
3. “Role of Enzymes in Biochemical Reactions.” Enzymes. N.p., n.d. Web. 20 May 2017. <http://chemistry.elmhurst.edu/vchembook/570enzymes.html>.
4. “Introduction to Enzymes.” Naming and Classification (Introduction to Enzymes). N.p., n.d. Web. 20 May 2017. <http://www.worthington-biochem.com/introbiochem/naming.html>.

Image Courtesy:
1. “Glucosidase enzyme” By Thomas Shafee – Own work (CC BY-SA 4.0) via Commons Wikimedia