The reaction mixture contained 200 µl of 50mM cysteine–20mM EDTA (disodium salt), pH 8.0, 700 µl 50mM Tris–HCl buffer, pH 8.0 and 100 µl enzyme solution. The mixture was incubated at 37 Ċ for 5 min before starting the reaction by adding 1ml of 1% (w/v) casein solution. After 10 min, the reaction was stopped by adding 3ml of 5% (v/v) trichloroacetic acid (TCA) and then cooled for 1 h