Biochemistry

Enzymes (Nomenclature)

Nomenclature of Enzymes

Enzymes are specialized protein complexes that serves as catalysts and are employed to accelerate the rate of reactions. Nomenclature or naming of enzymes can be:

Trivial Names

During early days, enzymes were given names by their discoverers in an arbitrary manner e.g. the names pepsin, trypsin and chymotrypsin convey no information about function of an enzyme or nature of substrate on which they act. Sometimes, suffix “ase” was added to the substrate for naming enzymes e.g. lipase acts on lipids, nuclease on nucleic acids, lactase on lactose etc. These are known as trivial names of enzymes which, however, fail to give complete information of enzyme reaction (type of reaction, co-factor requirement).

 

Enzymes are named by adding suffix “ase” to the name of substrate that they modify or type of reaction they catalyze e.g. Amylose is broken down into glucose molecules by the activity of enzyme called Amylase. Likewise, during glycolysis pathway various catalytic reactions occur and the most common reaction is removal of hydrogen which is done by an enzyme known as Dehydrogenase.

Except for some of originally studied enzymes such as pepsin, rennin, and trypsin, most enzyme names end in “ase”.

 

Enzyme Nomenclature

 

Enzyme Nomenclature by Enzyme Commission

The International Union of Biochemistry (I.U.B.) initiated standards of enzyme nomenclature which recommend that enzyme names indicate both the substrate acted upon and type of reaction catalyzed. Under this system, enzyme uricase is called urate: O2oxidoreductase, while the enzyme glutamic oxaloacetic transaminase (GOT) is called L-aspartate: 2-oxoglutarate aminotransferase.

The enzyme commission assign each enzyme a recommended name and a 4-part distinguishing number. EC numbers are four digits, for example a.b.c.d, where “a” is the class, “b” is the subclass, “c” is the sub-subclass, and “d” is the sub-sub-subclass. The “b” and “c” digits describe the reaction, while “d” digit is used to distinguish between different enzymes of same function based on actual substrate in the reaction. This enzyme classification does not take into account amino acid sequence (i.e. homology), protein structure, or chemical mechanism.

E.g. ATP: glucose phosphotransferase, which catalyzes the transfer of a phosphoryl group from ATP to glucose. As per E.C. number, it is denoted as 2.7.1.1. First number (2) denotes class name (transferase); second number (7) indicates subclass (phosphotransferase), third number (1), a phosphotransferase with a hydroxyl group as acceptor and fourth number (1) D-glucose as the phosphoryl group acceptor.

The enzyme commission (EC) divide enzymes into six main groups according to the type of reaction catalyzed which are:

  1. EC 1- Oxidoreductases
  2. EC 2- Transferases
  3. EC 3- Hydrolases
  4. EC 4- Lyases
  5. EC 5- Isomerases
  6. EC 6- Ligases

 

A complete list and description of thousands of known enzymes is maintained by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology.

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