PURIFICATION PROPERTIES AND N-TERMINAL SEQUENCE OF SHEEP TRYPSINOGEN

Sheep trypsinogen has been prepared from sheep pancreas in an apparently homogeneous state by two successive chromatographies on CM-cellulose. The purity of the enzyme has been checked by activity measurement, equilibrium chromatography, ultracentrifugation and polyacrylamide gel electrophoresis. Its amino acid composition has been determined. It differs only slightly from that of the bovine enzyme. Recent results concerning ovine trypsin reported by Travis are rather different from ours. Two different activation peptides have been isolated and their sequence determined. One is the hexapeptide Val-Asp-Asp-Asp-Asp-Lys identical to the bovine activation peptide, the other is the octapeptide Phe-Pro-Val-Asp-Asp-Asp-Asp-Lys, similar to the porcine activation peptide, but for the third residue which is Val in the sheep and Thr in the pig. The two peptides are N-terminal in trypsinogen, since Phe and Val are both N-terminal residues of DFP-trypsinogen. The two residues are in the same ratio as the two peptides. We conclude to the presence of two isoenzymes, although we have not been able to separate them by electrophoresis on polyacrylamide gels, using a set of different techniques. Our results on N-terminal sequence of ovine and caprine trypsinogen and the data of the literature on the bovine and porcine enzymes are compared with the known phylogenetic relationship between the Artiodactyls. © 1969.