Purification and characterization of a trypsin inhibitor from the egg of skipjack tuna Katsuwonus pelamis

A trypsin inhibitor was purified from the egg of skipjack tuna Katsuwonus pelamis by ammonium sulfate precipitation, gel filtration on a Sephadex G-100 column, ion-exchange chromatography on diethylaminoethyl-Sephacel, rechromatography on a Sephadex G-100 column and reversed-phase high-performance liquid chromatography on a C-18 column. The molecular mass of the purified trypsin inhibitor was approximately 78 kDa as estimated by gel filtration and 39 kDa by sodium dodecylsulfate polyacrylamide gel electrophoresis. The purified trypsin inhibitor was stable in the pH range from 4.0 to 10.0 and at temperatures below 40degreesC. The purified inhibitor was rich in Gly, Glu, Ser, Asp and Lys, but poor in Cys, Tyr, Phe, Ile and His. In addition, the activity of the purified trypsin inhibitor was increased in the presence of metal ions such as K+, Na+, Mg2+ and Ca2+.