The multiplicity of human pancreatic secretory trypsin inhibitor.

Four forms of pancreatic secretory trypsin inhibitor (PSTI; A1, A2, B, and C) were purified from human pancreatic juice. According to sequence results, the primary structure of B was different from that reported earlier (Greene, L.J., et al. (1976) Method Enzymol. 45, 813-825) at two positions, i.e. Asn21----Asp21, Asp29----Asn29. A1 and A2 were deamidated forms of B judging from peptide mappings with Staphylococcus aureus V8 protease. Gln45 in B was replaced by Glu in A1 and Gln51 in B was replaced by Glu in A2. C was an inhibitor lacking five amino acid residues from the amino terminal of B. B and C inhibited human cationic trypsin activity stoichiometrically with similar dissociation constants, but A1 and A2 showed poorer trypsin inhibitory activity than B and C.