Protease which breaks down milk proteins during the growth of the bacteria on milk. Endopeptidase activity with very broad specificity, although some subsite preference have been noted, e.g. large hydrophobic residues in the P1 and P4 positions, and Pro in the P2 position. Best known for its action on caseins, although it has been shown to hydrolyze hemoglobin and oxidized insulin B-chain. Belongs to the peptidase S8 family.