Two human trypsinogens. Purification, molecular properties, and N-terminal sequences

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Abstract
The 2 human trypsinogens were isolated from human pancreatic juice in a sufficient amount to study molecular and structural properties. The purification procedure included filtration on Sephadex G-100 followed by ion-exchange chromatography on DEAE-cellulose. The 2 trypsinogens represent 19% of total proteins of pancreatic juice. Trypsinogen 1, the major form, is present in a quantity twice that of trypsinogen 2, which is the most anionic protein in human pancreatic juice. The 2 proteins have partial immunological identity, close MW (23,438 and 25,006 for trypsinogens 1 and 2, respectively) and similar amino acid compositions. The N-terminal sequences are the same for the 1st 9 residues: Ala-Pro-Phe-Asp4-Lys-Ile. The 2 proteins differ in the activation peptides released during the transformation to trypsins. Trypsinogen 2 liberates 1 octapeptide Ala-Pro-Phe-Asp4-Lys while trypsinogen 1 liberates 2 peptides, the same octapeptide and the pentapeptide (Asp)4-Lys.