Inbiochemistry, aligase is anenzyme that cancatalyze the joining (ligation) of two molecules by forming a newchemical bond. This is typically viahydrolysis of a small pendant chemical group on one of the molecules, typically resulting in the formation of new C-O, C-S, or C-N bonds. For example,DNA ligase can join two complementary fragments of nucleic acid by forming phosphodiester bonds, and repair single stranded breaks that arise in double stranded DNA during replication.
In general, a ligase catalyzes the following dehydration reaction, thus joining molecules A and B:
A-OH + B-H → A–B + H2O
The naming of ligases is inconsistent and so these enzymes are commonly known by several different names. Generally, the common names of ligases include the word "ligase", such as inDNA ligase, an enzyme commonly used in molecular biologylaboratories to join togetherDNA fragments. However, many common names use the term "synthetase" or "synthase" instead, because they are used tosynthesize new molecules.[1] There are also some ligases that use the name "carboxylase" to indicate that the enzyme specifically catalyzes acarboxylation reaction.
To note: biochemical nomenclature has sometimes distinguished synthetases fromsynthases and sometimes treated the words assynonyms.[2] Commonly, the two terms are used interchangeably and are both used to describe ligases.
Ligases are classified asEC 6 in theEC number classification of enzymes. Ligases can be further classified into six subclasses:
Some ligases associate withbiological membranes asperipheral membrane proteins or anchored through a singletransmembrane helix,[3] for example certainubiquitin ligase related proteins.
The wordligase usescombining forms oflig- (from theLatin verbligāre, "to bind" or "to tie together") +-ase (denoting an enzyme), yielding "binding enzyme".
