(a) Effect of calcium ion (2 mM) and EDTA (2 mM) on the stability of the
purified tryspsin from Z. ophiocephalus. The stability was tested by incubating the
purified enzyme at 50 ◦C in the absence or presence of CaCl2 or EDTA and residual
enzyme activity was determined from 0 to 4 h 30 min at 30-min intervals. The
non-heated enzyme was considered as control (100% activity). (b) Effect of CaCl2
concentrations on the trypsin activity. The activity of the enzyme without CaCl2
was considered as 100%.