Ligase

Ligases
Enzyme classification
EC, category	6.-.-.-
Response type	Creating a covalent bond
Substrate	${\displaystyle \mathrm {M_{1}+M_{2}+NTP} }$
Products	${\displaystyle \mathrm {M_{1}{\mathord {-}}M_{2}+NDP+P\ oder\ M_{1}{\mathord {-}}M_{2}+NMP+2\ P} }$
Occurrence
Parent taxon	Creature

Ligases ( Latin ligare , 'to connect', 'to chain') are enzymes of the sixth enzyme class according to the systematic nomenclature of the enzyme commission of the International Union of Biochemistry (IUB), which catalyze the linking of two molecules through a covalent bond .

To do this, they need energy that comes from the cleavage of energy-rich nucleoside triphosphates (NTP) such as adenosine triphosphate (ATP). One or two phosphate residues (P) of the nucleotide are split off. Other molecules such as nicotinamide adenine dinucleotide (NAD) can also serve as energy suppliers. Since these can be regenerated by splitting ATP, the enzymes supplied with energy are also considered ligases.

Schematically, the ligase reaction proceeds as follows (M ₁ , M ₂ are the molecules to be connected):

${\displaystyle \mathrm {M_{1}+M_{2}+NTP\longrightarrow M_{1}{\mathord {-}}M_{2}+NDP+P\ oder\ M_{1}{\mathord {-}}M_{2}+NMP+2\ P} }$

classification

Ligases are categorized in the EC number classification system under EC  6.-.-.- . The second digit defines the more precise type of link:

• EC  6.1.-.- Linking carbon and oxygen
• EC  6.2.-.- Linking carbon and sulfur
• EC  6.3.-.- Linking carbon and nitrogen
• EC  6.4.-.- Linking of two carbon atoms
• EC  6.5.-.- Formation of a phosphoric ester
• EC  6.6.-.- Formation of a nitrogen-metal atom bond

Significant groups

A special subgroup of ligases are DNA ligases , often also called ligases for short . DNA ligases join (ligate) two strands of DNA by creating a phosphodiester bond . Thus, DNA ligases belong to class 6.5.

Another important group of ligases in biochemistry are the carboxylases . These enzymes store carbon dioxide in the form of carbonate ions on other molecules (EC 6.4.1.), For example pyruvate carboxylase .

Another biologically important group of ligases are the aminoacyl-tRNA synthetases . These enzymes load a tRNA with their specific amino acid in carboxylic acid ester bond while consuming ATP and thus belong to class 6.1.

The older term synthetase is still often used synonymously for ligases that also consume ATP. Synthetases should not be confused with synthases , which do not require additional energy for the addition reaction.

Other classes of enzymes

• Oxidoreductases ( EC  1.-.-.- )
• Transferases ( EC  2.-.-.- )
• Hydrolases ( EC  3.-.-.- )
• Lyases ( EC  4.-.-.- )
• Isomerases ( EC  5.-.-.- )
• Translocases ( EC 7.-.-.- )

literature

• Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6 edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
• Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .
• Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell , 5th Edition, Taylor & Francis 2007, ISBN 978-0815341062 .