Purification and characterization of trypsin-like enzymes from North Pacific krill (Euphausia pacifica)

Two trypsin-like enzymes (TLEs) were purified from North Pacific krill (Euphausia pacifica) by ammonium sulfate precipitation, ion-exchange and gel-filtration chromatography. The purified enzymes were identified as trypsins by LC-ESI-MS/MS analysis. The relative molecular mass of TLE I and TLE II were 33 and 32.3 kDa, respectively, with isoelectric points of 4.5 and 4.3, respectively. The TLEs showed excellent thermal stable in the crude extract and the purified TLEs were active over a wide pH (6.0-11.0) and temperature (10-70 degrees C) range. Compared with trypsins from other organisms, the purified TLEs had physiological efficiencies of 1.6-6.7-fold. The difference in Arg, Ile and Asp content might explain why E. pacifica TLEs have good thermal stability and physiological efficiency.