Hydrolysis of proteins with broad specificity similar to that of pepsin A, preferring hydrophobic residues at P1 and P1'. Clots milk and activates trypsinogen. Does not cleave 4-Gln-|-His-5, but does cleave 10-His-|-Leu-11 and 12-Val-|-Glu-13 in B chain of insulin. Belongs to the peptidase A1 family.