Temperature and pH sensitivity of trypsins from Atlantic salmon (Salmo salar) in comparison with bovine and porcine trypsin.

Four differently charged trypsins were purified from pyloric caeca of Atlantic salmon (Salmo salar). The isoelectric points of three anionic isoforms were 4.70, 4.60, and 4.55 (anionic trypsin I, II and III, respectively). And for the first time a cationic isoform (isoelectric point above 9.3) has been isolated from a marine species. The apparent molecular weights of all four isoforms were about 25 kDa as determined by SDS-PAGE. The salmon enzymes were inhibited by serine proteinase inhibitors in general and also by specific trypsin inhibitors. Anionic trypsin I and the cationic isoform were further examined. Anionic trypsin I showed the typical cold-adaptation features, low pH and temperature stability (also lower Gibb's free energy of GdnHCl-induced unfolding) and high catalytic efficiency as compared to the mammalian trypsins. The cationic isoform did not show these features, but resembled the mammalian trypsins.