Ligases (synthetases)
These enzymes (code EC 6) catalyze the linkage of two molecules coupled with the hydrolytic breakdown of a pyrophosphate bond in ATP or an analogous compound. The bonds formed are often high energy bonds. The second figure in the code number indicates the bond formed, e.g. C-O (6.1), C-S (6.2) etc. Examples include peptide synthase, aminoacyl-tRNA synthetase, DNA ligase and RNA ligase.