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Papain (EC2.22.4.3) is a thiol protease with high level of activity that has widespread industrial applications. The use of immobilized papain provides many advantages over its free form. In many applications, cysteine must be added as an activator. On the other hand, certain bivalent metal ions including Ca²⁺ behave as the inhibitors of papaein. In the present study, after preparation of Sepharose 6B with CNBr, a 5 mg/ml-protein solution was added to activate the gel for covalent attachment of enzyme and, subsequently, 2M glycine solution was added to block the remaining active groups on the gel.  The immobilization process brought about significant enhancement of storage, thermal stability, stability at extreme pHs, and resistance against the inhibitory effect of bivalent metal ions with respect to papain. The optimum temperature of papain was increased by 20 °C (from 60 to 80 °C) and its optimum pH was shifted from 7 to 8.0 upon immobilization. Also k_m and k_cat of the enzyme altered due to the immobilization process.These results are important in particular if one considers that the major problem in enzyme immobilization is the loss of enzyme activity and catalytic efficiency.

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Aims: Increasing the aquatic consumption, developing aquaculture, and the need for aquatic food production will make unclear the availability to fish oil in the future. The aim of this study was to investigate the effect of replacement of fish oil by grape seed oil on growth indices and protease enzymes activity in Rainbow Trout.
Materials & Methods: This study was conducted on 450 Rainbow Trout during a 60-day period. In this study, control diet (A) containing 100% fish oil and 25% (B), 50% (C), 75% (D), and 100% (E) grape seed oil were used instead of fish oil. The data were analyzed by Graph pad prism and SPSS 20 software, using one-way ANOVA test.
Findings: The highest final weight and weight gain was in diet C and the lowest was in D, having a significant difference. Specific Growth Rate (SGR) and Protein Efficiency Ratio (PER) had no significant difference. The highest and lowest feed conversion ratio (FCR) was observed in diets E and C, respectively, with a significant difference. The highest fat efficiency was in diet C. The highest feed efficiency was in diets C and D and the lowest was in E, and the diets were not significantly different. The most activity of pepsin and trypsin was observed in pyloric additions in diet C and in intestine in C and D. The optimal amount of fish oil replacement was satisfied by grape seed oil 50% (diet C).
Conclusion: The diet containing 50% fish oil and 50% grape seed oil is effective in improving the growth indices and activity of pepsin and trypsin enzymes in Rainbow Trout.

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Enzymes of marine organisms are ideal candidates for biomonitoring of pollution in marine environments. For the widespread use of enzymes in industrial processes, carried out under certain physico-chemical conditions, their stability must be improved. In this study, for the first time, chitosan nanoparticles were used as matrices for augmenting the stability of Penaeus vannamei (Whiteleg shrimp)-derived purified proteases against metallic ions. For the electrostatic binding of the enzyme to the chitosan nanoparticles, the protein solution at a concentration of 7mg/ml was added to the nanoparticles, and incubated for 4 hours at 10°C. After 3 times rinsing with phosphate buffer of pH=7.5, the nano-enzyme was dissolved in 1ml phosphate buffer, and used for further studies. The results of this study showed that Fe²⁺ and Mn²⁺ significantly increased the enzyme activity, whereas a strong inhibitory effect was observed in the presence of Cd²⁺, Hg²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺, and a weak inhibitory effect in the presence of Na⁺ and K⁺. The immobilized enzyme exhibited greater resistance to metal ions than its free counterpart. The free enzyme was susceptible to the presence of metal ions, and with the increment of their concentrations, enzyme activity declines. From this nexus, it could be inferred that the high stability of immobilized enzyme is due to the presence of chitosan nanoparticles. Stability retention of the immobilized enzyme at high concentrations of metal ions indicates the efficacy and utility of the immobilization method in industrial enzyme technology.