Ligases (Latin ligare, connect ',' link ' ) are enzymes of the sixth class of enzymes according to the systematic nomenclature of enzyme Commission of the International Union of Biochemistry (IUB ), which catalyze the linking of two molecules by a covalent bond. They need energy derived from the hydrolysis of high-energy nucleoside triphosphates (NTP). In this case, one or two phosphate residues are cleaved. Other molecules such as NAD can serve as an energy supplier. Since these can be regenerated among other things, ATP consumption, however, that thereby supplied with energy enzymes are also considered ligases.
Schematically, the ligase reaction proceeds as follows (M1, M2 are connected to the molecules) from:
Ligases in the EC numbers classification system under EC 6 -. -. - Categorized. The second digit defines the precise nature of the link:
- EC 6.1. -. - Combination of carbon and oxygen
- EC 6.2. -. - Linking of carbon and sulfur
- EC 6.3. -. - Linking carbon and nitrogen
- EC 6.4. -. - Linking two carbon atoms
- EC 6.5. -. - Formation of a phosphorus ester
- EC 6.6. -. - Formation of a nitrogen - metal atom bond
The term ligase is often used interchangeably for a specific subgroup, the DNA ligases, but this is not entirely correct. DNA ligases join ( ligated ) has two DNA strands, using a phosphoric diester is formed. Thus the flow of DNA ligases in the class 6.5.
The term is also often used synonymously synthetase, but is just as wrong as synthetases not generally use only NTPs and ATP. Synthetase should also not be confused with synthases, which do not require extra energy for the addition reaction.
Another major in biochemistry group are the carboxylases. These enzymes store carbon dioxide in the form of carbonate ions to other molecules ( EC 6.4.1. ).
- Pyruvate carboxylase
- Aminoacyl -tRNA synthetase
Other enzyme classes
- Oxidoreductases ( EC 1 -. -. - )
- Transferases ( EC 2 -. -. - )
- Hydrolases ( EC 3 -. -. - )
- Lyases ( EC 4 -. -. - )
- Isomerases ( EC 5 -. -. - )