ENTRY       EC 3.4.23.1
NAME        Pepsin A
            Pepsin
CLASS       Hydrolases
            Acting on peptide bonds (peptidases)
            Aspartic endopeptidases
REACTION    Preferential cleavage: hydrophobic, preferably aromatic, residues
            in P1 and P1' positions.  Cleaves Phe1+Val, Gln4+His, Glu13+Ala,
            Ala14+Leu, Leu15+Tyr, Tyr16+Leu, Gly23+Phe, Phe24+Phe and
            Phe25+Tyr bonds in the B chain of insulin
SUBSTRATE   Protein
            Peptide
            H2O
PRODUCT     Protein
            Peptide
INHIBITOR   Methyl 2-diazoacetamidohexonate
COMMENT     The predominant endopeptidase in the gastric juice of vertebrates,
            formed from pepsinogen A by limited proteolysis.  Human pepsin A
            occurs in five molecular forms.  Pig pepsin D is
            unphosphorylated pepsin A.  Formerly EC 3.4.4.1.
DISEASE     MIM: 169710  Pepsinogen A3
            MIM: 169720  Pepsinogen A4
            MIM: 169730  Pepsinogen A5
MOTIF       PS: PS00141  [LIVMFGAC]-[LIVMTADN]-[LIVFSA]-D-[ST]-G-[STAV]-
                         [STAPDENQ]-x-[LIVMFSTNC]-x-[LIVMFGTA]
GENES       HSA: PGA3 PGA4 PGA5
STRUCTURES  PDB: 1PSA  1PSN  1PSO  3PEP  4PEP  5PEP  
DBLINKS     University of Geneva ENZYME DATA BANK: 3.4.23.1
            WIT (What Is There) Metabolic Reconstruction: 3.4.23.1
            SCOP (Structural Classificaion of Proteins): 3.4.23.1
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