Hydrolyzes a variety of proteins. Broad specificity similar to that of pepsin A. Clots milk by cleavage of a single 104-Ser-Phe-|-Met-Ala-107 bond in kappa-chain of casein. Inhibited by pepstatin. Optimum pH is about 2.5. Monomer. Expressed in adult, not neonate-specific as in other organisms. Belongs to the peptidase A1 family.