Partial characterization of alkaline proteases from viscera of vermiculated sailfin catfish Pterygoplichthysdisjunctivus Weber, 1991

Vermiculated sailfin catfish (Pterygoplichthys disjunctivus, Weber, 1991), a member of the Loricariidae family and an invasive species of several inland waters around the world, possess an enormous digestive tract representing about 10% of fish weight. Thus, the aim of this study was to partially characterize proteases from their digestive tracts. Azocasein digestion of the crude extract of intestine at different pH values and temperatures revealed the presence of alkaline proteases with optimum activities at pH 9.0 and 50°C. Incubation assays of the crude extract with inhibitors such as phenyl methyl sulfonyl fluoride, N-α-p-tosyl-l-lysine chloromethyl ketone, N-tosyl-phenyalanine chloromethyl ketone, benzamidine, pepstatin A and ethylenediamine tetra-acetic acid showed that trypsin and chymotrypsin are the main alkaline proteinases present. Zymography showed that the crude extract of Pterygoplichthysdisjunctivus viscera contained proteases with molecular masses ranging from 21.5 to 116 kDa. Trypsin and chymotrypsin were inhibited by the following ions in decreasing order: Hg2+, Fe2+, Cu2+, Li+, Mg2+, K+, while Mn2+, and Ca2+ had no effect. Activities decreased continuously as the NaCl concentration increased from 0 to 30%. These results constitute important background information for future studies and for the potential biotechnological use of the crude digestive extract from this invasive species.