1. Oxidoreductases

 2. Transferases

 3. Hydrolases

 4. Lyases

 5. Isomerases

 6. Ligases

   6.1  Forming carbon-oxygen bonds

   6.2  Forming carbon-sulfur bonds

   6.3  Forming carbon-nitrogen bonds

     6.3.1  Acid-D-ammonia (or amine) ligases (amide synthases)

     6.3.2  Acid-D-amino-acid ligases (peptide synthases)

     6.3.3  Cyclo-ligases

     6.3.4  Other carbon-nitrogen ligases

       6.3.4.2  CTP synthase (glutamine hydrolysing)

       6.3.4.3  formate---tetrahydrofolate ligase

       6.3.4.4  adenylosuccinate synthase

       6.3.4.5  argininosuccinate synthase

       6.3.4.6  urea carboxylase

       6.3.4.7  ribose-5-phosphate---ammonia ligase

       6.3.4.8  imidazoleacetate---phosphoribosyldiphosphate ligase

       6.3.4.9  biotin---[methylmalonyl-CoA-carboxytransferase] ligase

       6.3.4.10  biotin---[propionyl-CoA-carboxylase (ATP-hydrolysing)] ligase

       6.3.4.11  biotin---[methylcrotonoyl-CoA-carboxylase] ligase

       6.3.4.12  glutamate---methylamine ligase

       6.3.4.13  phosphoribosylamine---glycine ligase

       6.3.4.14  biotin carboxylase

       6.3.4.15  biotin---[biotin carboxyl-carrier protein] ligase

       6.3.4.16  carbamoyl-phosphate synthase (ammonia)

       6.3.4.17  formate---dihydrofolate ligase

       6.3.4.18  5-(carboxyamino)imidazole ribonucleotide synthase

       6.3.4.19  tRNAIle-lysidine synthase

       6.3.4.20  7-cyano-7-deazaguanine synthase

       6.3.4.21  nicotinate phosphoribosyltransferase

       6.3.4.22  tRNAIle2-agmatinylcytidine synthase

       6.3.4.23  formate---phosphoribosylaminoimidazolecarboxamide ligase

       6.3.4.24  tyramine---L-glutamate ligase

       6.3.4.25  2-amino-2'-deoxyadenylo-succinate synthase

     6.3.5  Carbon-nitrogen ligases with glutamine as amido-N-donor

   6.4  Forming carbon-carbon bonds

   6.5  Forming phosphoric-ester bonds

   6.6  Forming nitrogen-metal bonds

   6.7  Forming nitrogen-nitrogen bonds

 7. Translocases