Secreted aspartic endopeptidase that allows assimilation of proteinaceous substrates. The scissile peptide bond is attacked by a nucleophilic water molecule activated by two aspartic residues in the active site. Shows a broad primary substrate specificity. Favors hydrophobic residues at the P1 and P1' positions, but also accepts a lysine residue in the P1 position, leading to the activation of trypsinogen and chymotrypsinogen A. Hydrolysis of proteins with broad specificity. Generally favors hydrophobic residues in P1 and P1', but also accepts Lys in P1, which leads to activation of trypsinogen. Does not clot milk. Monomer. Expressed, albeit at a very low level. Belongs to the peptidase A1 family.