Shows particularly broad specificity; although bonds involving phenylalanine and leucine are preferred, many others are also cleaved to some extent. Preferential cleavage: hydrophobic, preferably aromatic, residues in P1 and P1' positions. Cleaves 1-Phe-|-Val-2, 4-Gln-|-His-5, 13-Glu-|-Ala-14, 14-Ala-|-Leu-15, 15-Leu-|-Tyr-16, 16-Tyr-|-Leu-17, 23-Gly-|-Phe-24, 24-Phe-|-Phe-25 and 25-Phe-|-Tyr-26 bonds in the B chain of insulin. Early postnatal. Belongs to the peptidase A1 family.