_EC 6.3.-.- Forming carbon-nitrogen bonds. 1,455 PDB entries  
EC 6.-.-.- Ligases. [3,414 PDB entries]
EC 6.3.-.- Forming carbon-nitrogen bonds. [1,455 PDB entries]
EC 6.3.1.- Acid--ammonia (or amine) ligases (amide synthases). [151 PDB entries]
EC 6.3.2.- Acid--amino-acid ligases (peptide synthases). [502 PDB entries]
EC 6.3.3.- Cyclo-ligases. [138 PDB entries]
EC 6.3.4.- Other carbon--nitrogen ligases. [495 PDB entries]
EC 6.3.5.- Carbon--nitrogen ligases with glutamine as amido-N-donor. [169 PDB entries]