Similar results of optimum temperature and thermostability were found for trypsins from other tropical fish, such
as: P. maculatus (55 and 45 °C, respectively) ( Souza et al., 2007) and C. macropomum (60 and 55 °C, respectively) ( Bezerra et al., 2001). Fuchise et al. (2009) found an optimum temperature of 50 °C for trypsins of Gadus macrocephalus and E. gracilis. These results showed that even some species that live in cold waters have trypsins that present an optimum temperature similar to that of tropical and temperate zone fish trypsins. It is not known why the digestive enzymes from fish and other aquatic organisms present high activity at temperatures well above the habitat temperature. Probably, the answer to this question lies in the need for adaptations Autophagy inhibitor and natural selection of their ancestors due to climate changes that took place during their evolution. Some enzymes require an additional chemical component (cofactor), such
as inorganic ions, to be active. On the other hand, heavy metals constitute one of the main groups of aquatic pollutants. The effect of metallic ions (1 mM) on the activity of enzyme was evaluated and is presented in Table 3. At this concentration, the ions K+, Mg2+and Ba2+ did not promote any significant effect click here on enzyme activity. However, A. gigas trypsin was shown to be more sensitive to divalent (Cd2+, Cu2+, Fe2+, Hg2+, Zn2+ and Pb2+) and especially to trivalent (Al3+) cations. The ion Ca2+ has been reported in the literature as a trypsin activator in several organisms, especially mammals. However, pirarucu trypsin was slightly inhibited in the presence of low concentrations of this ion (1 mM). This same effect has been observed for trypsins from other tropical fish, such as Nile tilapia (O. niloticus) ( Bezerra et al., 2005) and spotted goatfish (P. maculatus) ( Souza et al., 2007).
These findings point to a possible difference in the structure of the primary calcium-binding site between mammalian pancreatic trypsin and the trypsin from these fish ( Bezerra et al., 2005). A recent study, based on the use of fluorescent protease substrates and commercial inhibitors Niclosamide has indicated that fish trypsins may differ in structure and catalytic mechanism, when compared to mammalian enzymes ( Marcuschi et al., 2010). Previous studies have shown that trypsin-like enzymes from other tropical fish also showed sensitivity to metallic ions ( Bezerra et al., 2001, Bezerra et al., 2005, Bougatef et al., 2007 and Souza et al., 2007), especially Cd2+, Al3+, Zn2+, Cu2+, Pb2+ and Hg2+ (1 mM). It is known that Cd2+, Co2+ and Hg2+ act on sulphhydryl residues in proteins and Bezerra et al. (2005) report that the strong inhibition promoted by these metallic ions demonstrates the relevance of sulfhydryl residues in the catalytic action of this protease.