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. Optimum pH is 3.5. Optimum temperature is 50 degrees Celsius. Monomer. Repressed by alkaline pH and in presence of ammonia. Used in the production of blue cheese. During the fermentation process, aspartic protease hydrolyzes casein which leads to clotting of the milk. Belongs to the peptidase A1 family.