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 can also activate trypsinogen and hydrolyze the B chain of insulin between positions 'Gly-20' and 'Glu-21'. Hydrolysis of proteins with broad specificity similar to that of pepsin A, preferring hydrophobic residues at P1 and P1', but also cleaving 20-Gly-|-Glu-21 in the B chain of insulin. Clots milk, and activates trypsinogen. Monomer. Belongs to the peptidase A1 family. PubMed:10850809 has identified a second propeptide cleavage site after Lys-68 and both possible mature proteins were found in equal quantities in a heterologous expression system in Aspergillus awamori.