Giant Amazonian fish pirarucu (Arapaima gigas): Its viscera as a source of thermostable trypsin

A trypsin was purified from pyloric caeca of pirarucu (Arapaima gigas). The effect of metal ions and protease inhibitors on its activity and its physicochemical and kinetic properties, as well its N-terminal sequence, were determined. A single band (28.0kDa) was observed by SDS–PAGE. Optimum pH and temperature were 9.0 and 65°C, respectively. The enzyme was stable after incubation for 30min in a wide pH range (6.0–11.5) and at 55°C. The kinetic parameters Km, kcat and kcat/Km were 0.47±0.042mM, 1.33s−1 and 2.82s−1mM−1, respectively, using BApNA as substrate. This activity was shown to be very sensitive to some metal ions, such as Fe2+, Hg2+, Zn2+, Al3+, Pb2+, and was highly inhibited by trypsin inhibitors. The trypsin N-terminal sequence IVGGYECPRNSVPYQ was found. The features of this alkaline peptidase suggest that it may have potential for industrial applications (e.g. food and detergent industries).