ABSTRACT
Trypsin (EC 3.1.21.4) is an important pancreatic serine protease synthesized as a proenzyme by pancreatic acinar cells and is secreted into the intestine of mammals. Mammalian pancreatic trypsin and its proenzyme have been extensively characterized (Walsh 1970, Kossiakoff et al. 1977). Fish trypsin is similar to mammalian pancreatic trypsin in its molecular weight, amino acid composition, Ca2 requirement, and reaction with substrates and/or inhibitors. cDNAs encoding trypsins from Atlantic cod and salmon have been isolated (Gudmundsdottir et al. 1993, Male et al. 1995). Fish trypsin has distribution patterns of charged and hydrophobic amino acid residues similar to mammalian trypsin, indicating similar three-dimensional structures. Trypsins from some marine invertebrates have been purified and characterized (Gates & Travis 1969, Winter & Neurath 1970). The characteristics of the enzymes from marine invertebrates resemble those of mammalian pancreatic trypsin in molecular weight, cleavage specificities, and reaction with inhibitors. The structural study on the active site of trypsin from the starfish Dermasterias imbricata showed that the amino acid composition of the peptide from the active site of the trypsin is similar to that of mammalian pancreatic trypsin (Camacho et al. 1976). However, marine invertebrate trypsins are unstable at acidic pH and are not activated or stabilized by adding calcium ions, unlike mammalian pancreatic trypsin. These findings suggest that notable structural differences exist between mammalian pancreatic and starfish trypsins. In the present study, we purified a trypsin from the pyloric ceca of the starfish
Asterias amurensis, and examined its characteristics and N-terminal amino acid sequence.
