The disulfide bridges of the immunoreactive forms of human pancreatic stone protein isolated from pancreatic juice

Following the complete sequence elucidation of human pancreatic stone protein (immunoreactive form PSP S1 isolated from pancreatic juice) [(1987) Eur. J. Biochem. 168, 201-207], the location of the three S-S bridges of the protein was investigated. The cystine-containing peptides, detected after the separation of the peptic or chymotryptic digests on SP-Sephadex or Sephadex G-50, were submitted to Edman degradation and/or to oxidation. The cysteic peptides after separation on SP-Sephadex or Sephadex G-50 were characterized by their amino acid compositions. The pairing of the half-cystines: Cys 3-Cys 14, Cys 31-Cys 129 and Cys 104-Cys 121 was determined. The same experiments carried out with PSP S2-5 (other immunoreactive forms) gave an identical characterization.