Kinetic Properties of Three Isoforms of Trypsin Isolated from the Pyloric Caeca of Chum Salmon ( Oncorhynchus keta )

Three isoforms of anionic chum salmon trypsin (ST-1, ST-2, and ST-3) were purified from the pyloric caeca of chum salmon (Oncorhynchus keta). The molecular weights of the three isoforms were about 24 kDa as determined by SDS-PAGE. The isoelectric points of ST-1, ST-2, and ST-3 were 5.8, 5.4, and 5.6, respectively. The apparent Km values of two isoforms (ST-1 and ST-2) for BAPA (benzoyl-L-arginine-p-nitroanilide) hydrolysis at 5, 15, 25 and 35 °C were slightly higher than that of the main isoform ST-3, depending on temperature. The turnover numbers, kcat, of ST-1 and ST-2 were about twice as high as that of ST-3. Consequently, the catalytic efficiencies (kcat/Km) of ST-1 and ST-2 were more efficient than ST-3. There were marked differences in both apparent Km and kcat values of three anionic chum salmon trypsins as compared to bovine cationic trypsin. Km values of all chum salmon trypsins were approximately 10 times lower than those of bovine trypsin, depending on the temperature. The kcat values of all chum salmon trypsins were about 2- to 5-fold higher than those of bovine trypsin; therefore, the catalytic efficiencies (kcat/Km) of chum salmon trypsin were 20- to 40-fold more efficient than those of bovine trypsin. On the other hand, kcat/Km values of ST-1 for TAME (tosyl-L-arginine methyl ester) hydrolysis were lower than those of bovine trypsin, whereas kcat/Km values of ST-2 and ST-3 were comparable to those of bovine trypsin, depending on the temperature.