Shows particularly broad specificity; although bonds involving phenylalanine and leucine are preferred, many others are also cleaved to some extent (By similarity). May play a role as a specialized neonatal digestive enzyme (Probable). 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. Inhibited by pepstatin A. Expressed in glandular chief cells of the neonatal stomach. Expressed in yolk sacs of the placenta (at protein level). In neonatal stomach, highly expressed for the first two weeks after birth, with rapidly decreasing expression after 17.5 days. In placenta, detected from 11.5 dpc until term. Belongs to the peptidase A1 family.