_EC 3.4.21.- Serine endopeptidases. 2,655 PDB entries  
EC 3.-.-.- Hydrolases. [22,802 PDB entries]
EC 3.4.-.- Acting on peptide bonds (peptide hydrolases). [7,378 PDB entries]
EC 3.4.21.- Serine endopeptidases. [2,655 PDB entries]    
EC 3.4.21.1 Chymotrypsin. [66 PDB entries]
EC 3.4.21.2 Chymotrypsin C. [2 PDB entries]
EC 3.4.21.3 Metridin. [-]
EC 3.4.21.4 Trypsin. [556 PDB entries]
EC 3.4.21.5 Thrombin. [389 PDB entries]
EC 3.4.21.6 Coagulation factor Xa. [134 PDB entries]
EC 3.4.21.7 Plasmin. [30 PDB entries]
EC 3.4.21.8 Transferred entry: 3.4.21.34 and 3.4.21.35. [-]
EC 3.4.21.9 Enteropeptidase. [2 PDB entries]
EC 3.4.21.10 Acrosin. [2 PDB entries]
EC 3.4.21.11 Transferred entry: 3.4.21.36 and 3.4.21.37. [-]
EC 3.4.21.12 Alpha-lytic endopeptidase. [48 PDB entries]
EC 3.4.21.13 Transferred entry: 3.4.16.5 and 3.4.16.6. [-]
EC 3.4.21.14 Transferred entry: 3.4.21.62, 3.4.21.63, 3.4.21.64, 3.4.21.65 and [1 PDB entries]
EC 3.4.21.15 Transferred entry: 3.4.21.63. [-]
EC 3.4.21.16 Deleted entry. [-]
EC 3.4.21.17 Deleted entry. [-]
EC 3.4.21.18 Deleted entry. [-]
EC 3.4.21.19 Glutamyl endopeptidase. [4 PDB entries]
EC 3.4.21.20 Cathepsin G. [4 PDB entries]
EC 3.4.21.21 Coagulation factor VIIa. [66 PDB entries]
EC 3.4.21.22 Coagulation factor IXa. [23 PDB entries]
EC 3.4.21.23 Deleted entry. [-]
EC 3.4.21.24 Deleted entry. [-]
EC 3.4.21.25 Cucumisin. [1 PDB entries]
EC 3.4.21.26 Prolyl oligopeptidase. [32 PDB entries]
EC 3.4.21.27 Coagulation factor XIa. [50 PDB entries]
EC 3.4.21.28 Transferred entry: 3.4.21.74. [-]
EC 3.4.21.29 Transferred entry: 3.4.21.74. [-]
EC 3.4.21.30 Transferred entry: 3.4.21.74. [-]
EC 3.4.21.31 Transferred entry: 3.4.21.68 and 3.4.21.73. [-]
EC 3.4.21.32 Brachyurin. [1 PDB entries]
EC 3.4.21.33 Deleted entry. [-]
EC 3.4.21.34 Plasma kallikrein. [4 PDB entries]
EC 3.4.21.35 Tissue kallikrein. [9 PDB entries]
EC 3.4.21.36 Pancreatic elastase. [117 PDB entries]
EC 3.4.21.37 Leukocyte elastase. [10 PDB entries]
EC 3.4.21.38 Coagulation factor XIIa. [4 PDB entries]
EC 3.4.21.39 Chymase. [18 PDB entries]
EC 3.4.21.40 Deleted entry. [-]
EC 3.4.21.41 Complement subcomponent C1r. [5 PDB entries]
EC 3.4.21.42 Complement subcomponent C1s. [7 PDB entries]
EC 3.4.21.43 Classical-complement-pathway C3/C5 convertase. [5 PDB entries]
EC 3.4.21.44 Transferred entry: 3.4.21.43. [-]
EC 3.4.21.45 Complement factor I. [1 PDB entries]
EC 3.4.21.46 Complement factor D. [13 PDB entries]
EC 3.4.21.47 Alternative-complement-pathway C3/C5 convertase. [11 PDB entries]
EC 3.4.21.48 Cerevisin. [-]
EC 3.4.21.49 Hypodermin C. [2 PDB entries]
EC 3.4.21.50 Lysyl endopeptidase. [5 PDB entries]
EC 3.4.21.51 Deleted entry. [-]
EC 3.4.21.52 Deleted entry. [-]
EC 3.4.21.53 Endopeptidase La. [13 PDB entries]
EC 3.4.21.54 Gamma-renin. [-]
EC 3.4.21.55 Venombin Ab. [-]
EC 3.4.21.56 Deleted entry. [-]
EC 3.4.21.57 Leucyl endopeptidase. [-]
EC 3.4.21.58 Deleted entry. [-]
EC 3.4.21.59 Tryptase. [22 PDB entries]
EC 3.4.21.60 Scutelarin. [-]
EC 3.4.21.61 Kexin. [3 PDB entries]
EC 3.4.21.62 Subtilisin. [108 PDB entries]
EC 3.4.21.63 Oryzin. [-]
EC 3.4.21.64 Peptidase K. [64 PDB entries]
EC 3.4.21.65 Thermomycolin. [-]
EC 3.4.21.66 Thermitase. [4 PDB entries]
EC 3.4.21.67 Endopeptidase So. [-]
EC 3.4.21.68 T-plasminogen activator. [10 PDB entries]
EC 3.4.21.69 Protein C (activated). [4 PDB entries]
EC 3.4.21.70 Pancreatic endopeptidase E. [-]
EC 3.4.21.71 Pancreatic elastase Ii. [1 PDB entries]
EC 3.4.21.72 IgA-specific serine endopeptidase. [1 PDB entries]
EC 3.4.21.73 U-plasminogen activator. [111 PDB entries]
EC 3.4.21.74 Venombin A. [-]
EC 3.4.21.75 Furin. [4 PDB entries]
EC 3.4.21.76 Myeloblastin. [1 PDB entries]
EC 3.4.21.77 Semenogelase. [5 PDB entries]
EC 3.4.21.78 Granzyme A. [2 PDB entries]
EC 3.4.21.79 Granzyme B. [3 PDB entries]
EC 3.4.21.80 Streptogrisin A. [5 PDB entries]
EC 3.4.21.81 Streptogrisin B. [28 PDB entries]
EC 3.4.21.82 Glutamyl endopeptidase Ii. [1 PDB entries]
EC 3.4.21.83 Oligopeptidase B. [1 PDB entries]
EC 3.4.21.84 Limulus clotting factor C. [-]
EC 3.4.21.85 Limulus clotting factor B. [-]
EC 3.4.21.86 Limulus clotting enzyme. [-]
EC 3.4.21.87 Transferred entry: 3.4.23.49. [-]
EC 3.4.21.88 Repressor LexA. [11 PDB entries]
EC 3.4.21.89 Signal peptidase I. [9 PDB entries]
EC 3.4.21.90 Togavirin. [34 PDB entries]
EC 3.4.21.91 Flavivirin. [98 PDB entries]
EC 3.4.21.92 Endopeptidase Clp. [44 PDB entries]
EC 3.4.21.93 Proprotein convertase 1. [3 PDB entries]
EC 3.4.21.94 Proprotein convertase 2. [-]
EC 3.4.21.95 Snake venom factor V activator. [5 PDB entries]
EC 3.4.21.96 Lactocepin. [-]
EC 3.4.21.97 Assemblin. [22 PDB entries]
EC 3.4.21.98 Hepacivirin. [258 PDB entries]
EC 3.4.21.99 Spermosin. [-]
EC 3.4.21.100 Sedolisin. [9 PDB entries]
EC 3.4.21.101 Xanthomonalisin. [-]
EC 3.4.21.102 C-terminal processing peptidase. [10 PDB entries]
EC 3.4.21.103 Physarolisin. [-]
EC 3.4.21.104 Mannan-binding lectin-associated serine protease-2. [6 PDB entries]
EC 3.4.21.105 Rhomboid protease. [28 PDB entries]
EC 3.4.21.106 Hepsin. [5 PDB entries]
EC 3.4.21.107 Peptidase Do. [40 PDB entries]
EC 3.4.21.108 HtrA2 peptidase. [2 PDB entries]
EC 3.4.21.109 Matriptase. [20 PDB entries]
EC 3.4.21.110 C5a peptidase. [1 PDB entries]
EC 3.4.21.111 Aqualysin 1. [1 PDB entries]
EC 3.4.21.112 Site-1 protease. [-]
EC 3.4.21.113 Pestivirus NS3 polyprotein peptidase. [26 PDB entries]
EC 3.4.21.114 Equine arterivirus serine peptidase. [-]
EC 3.4.21.115 Infectious pancreatic necrosis birnavirus Vp4 peptidase. [3 PDB entries]
EC 3.4.21.116 SpoIVB peptidase. [-]
EC 3.4.21.117 Stratum corneum chymotryptic enzyme. [5 PDB entries]
EC 3.4.21.118 Kallikrein 8. [1 PDB entries]
EC 3.4.21.119 Kallikrein 13. [1 PDB entries]
EC 3.4.21.120 Oviductin. [-]
EC 3.4.21.121 Lys-Lys/Arg-Xaa endopeptidase. [-]

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