3.2.4. Effects of metal ions, surfactants and oxidising agents on
protease stability
The effects of several metal ions, at a concentration of 5 mM, on the activity of S. basilisca trypsin were studied at pH 9.5 and 60 C (Table 2). The addition of CaCl2 and MnCl2 increased protease activity to 114% (p < 0.05). This ion stimulating effect of enzyme activity, and especially by Ca2+, was reported by Sipost and Merkelt (1970) on the activity of trypsin. Indeed, they concluded that the function of calcium is to maintain a specific compact conformation of the enzyme molecules, which is necessary for their optimal catalytic activity. Mg2+ and Ba2+ decreased the protease activity by
about 14% and 30%, respectively. However, Hg2+, Zn2+, Fe2+ and Cu2+ affected the enzyme activity greatly with 100% inhibition. The inhibition by Mg2+ and Ba2+ was similar to that obtained for cuttlefish trypsin. Indeed, it retains about 17% and 27% of its activity when incubated with 5 mM Mg2+ and Ba2+, respectively (Baltiet al., 2009). The presence of NaCl and KCl did not affect the proteolytic activity.