_EC 3.1.-.- Acting on ester bonds. 5,948 PDB entries  
EC 3.-.-.- Hydrolases. [20,839 PDB entries]
EC 3.1.-.- Acting on ester bonds. [5,948 PDB entries]    
EC 3.1.1.- Carboxylic ester hydrolases. [948 PDB entries]
EC 3.1.2.- Thiolester hydrolases. [82 PDB entries]
EC 3.1.3.- Phosphoric monoester hydrolases. [1,339 PDB entries]
EC 3.1.4.- Phosphoric diester hydrolases. [455 PDB entries]
EC 3.1.5.- Triphosphoric monoester hydrolases. [-]
EC 3.1.6.- Sulfuric ester hydrolases. [12 PDB entries]
EC 3.1.7.- Diphosphoric monoester hydrolases. [19 PDB entries]
EC 3.1.8.- Phosphoric triester hydrolases. [75 PDB entries]
EC 3.1.11.- Exodeoxyribonucleases producing 5'-phosphomonoesters. [47 PDB entries]
EC 3.1.13.- Exoribonucleases producing 5'-phosphomonoesters. [935 PDB entries]
EC 3.1.14.- Exoribonucleases producing 3'-phosphomonoesters. [-]
EC 3.1.15.- Exonucleases active with either ribo- or deoxyribonucleic acid an [-]
EC 3.1.16.- Exonucleases active with either ribo- or deoxyribonucleic acid an [-]
EC 3.1.21.- Endodeoxyribonucleases producing 5'-phosphomonoesters. [141 PDB entries]
EC 3.1.22.- Endodeoxyribonucleases producing other than 5'-phosphomonoesters. [18 PDB entries]
EC 3.1.23.- (not defined) [-]
EC 3.1.24.- (not defined) [-]
EC 3.1.25.- Site-specific endodeoxyribonucleases specific for altered bases. [6 PDB entries]
EC 3.1.26.- Endoribonucleases producing 5'-phosphomonoesters. [1,208 PDB entries]
EC 3.1.27.- Endoribonucleases producing other than 5'-phosphomonoesters. [421 PDB entries]
EC 3.1.30.- Endoribonucleases active with either ribo- or deoxyribonucleic ac [11 PDB entries]
EC 3.1.31.- Endoribonucleases active with either ribo- or deoxyribonucleic ac [231 PDB entries]

[-] signifies that there are no PDB entries for the given enzyme subclass