Enzymes: Enzyme-naming conventions

By common convention, an enzyme's name consists of a description of what it does, with the word ending in -ase. Examples are alcohol dehydrogenase and DNA polymerase. Kinases are enzymes that transfer phosphate groups. This results in different enzymes with the same function having the same basic name; they are therefore distinguished by other characteristics, such as their optimal pH (alkaline phosphatase) or their location (membrane ATPase). Furthermore, the reversibility of chemical reactions means that the normal physiological direction of an enzyme's function may not be that observed under laboratory conditions. This can result in the same enzyme being identified with two different names: one stemming from the formal laboratory identification as described above, the other representing its behavior in the cell. For instance the enzyme formally known as xylitol:NAD+ 2-oxidoreductase (D-xylulose-forming) is more commonly referred to in the cellular physiological sense as D-xylulose reductase, reflecting the fact that the function of the enzyme in the cell is actually the reverse of what is often seen under in vitro conditions.

The International Union of Biochemistry and Molecular Biology has developed a nomenclature for enzymes, the EC numbers; each enzyme is described by a sequence of four numbers, preceded by "EC". The first number broadly classifies the enzyme based on its mechanism:

The toplevel classification is

- EC 1 Oxidoreductases: catalyze oxidation/reduction reactions

- EC 2 Transferases: transfer a functional group (e.g. a methyl or phosphate group)

- EC 3 Hydrolases: catalyze the hydrolysis of various bonds

- EC 4 Lyases: cleave various bonds by means other than hydrolysis and oxidation

- EC 5 Isomerases: catalyze isomerization changes within a single molecule

-EC 6 Ligases: join two molecules with covalent bonds

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