Effect of pH on activity and stability of Z. ophiocephalus
trypsin
The pH activity profile of the purified Z. ophiocephalus trypsin was investigated at 25 ◦C between pH 6.0 and pH 12.0. As can be seen in Fig. 3a, the optimum pH value of the purified enzyme was 9.0. The relative activities at pH 10.0 and 11.0 were about 91% and 50%, respectively, of that at pH 9.0. Therefore, Z. ophiocephalus trypsin could be a potential candidate for addition in commercial laundry detergents, because the pH in laundry detergent is generally in the range of 9.0–11.0. The optimum pH activity of Z. ophiocephalus trypsin was higher than that of trypsin from S. officinalis, which showed maximum activity at pH 8.0 [7] and that of trypsin from D. rhombeus which exhibited higher enzyme activity at pH 8.5 [12]. However, the optimum pH was lower than that of B. capriscus trypsin which exhibited maximum activity at
pH 10.5 and showed about 91% activity at pH 11.0 [10]. The pH stability profile of trypsin from Z. ophiocephalus is shown
in Fig. 3b. The enzyme is highly stable in a broad pH range, and more than 95% activity was retained even after incubation for 1 h at 25 ◦C at pH between 7.0 and 11.0. However, it was unstable at pH 12.0. The pH stability of
Z. ophiocephalus trypsin is higher than montereysardine trypsin, which was stable in the pH range from 7.0 to 8.0 [33] and D. rhombeus trypsin, which maintained over 85% of its optimum activity between pH 8.5 and 11.0 [12]. These results suggest that the viscera of goby would be a potential source of trypsin for certain food processing operations that require high alkaline conditions.