Digestive enzymes of large cabbage white butterfly, Pieris brassicae L. (Lepidoptera: Pieridae) from developmental and site of activity perspectives

Abstract

Investigation of digestive enzymes in the alimentary tract of insects is very important for knowledge on physiology of nutrition. The overall results of this study showed the presence of the majority of digestive enzymes including α-amylase, α- and β-glucosidase and galactosidase, lipases and proteases in the midgut of Pieris brassicae. It was found that the fourth and fifth instar larvae had the highest enzymatic activity, but the obvious differences were found in the cases of sites of enzyme activity known as soluble and membrane-bound fractions. The highest enzymatic activities in the soluble fractions were found in cases of α-amylase, lipases and proteinases such as trypsin-like, chymotrypsin-like and elastase. In contrast, glycosidases and exopeptidases (amino and carboxypeptidases) demonstrated the highest enzymatic activity in the membrane-bound fractions. However, no enzymatic activity was observed on cysteine protease as a type of proteinases. By using line regression, parameter β (slope) showed larval dependency on enzymes along with developmental and feeding processes. It was found that α-glucosidase had the highest slope and the membrane-bound fraction of general proteases had the lowest, showing high and low dependencies of larvae to α-glucosidase and exopeptidases, respectively, in addition to second priority on β-glucosidase and α-amylase. Optimal pHs of soluble and membrane-bound α-amylase were found at 9 while all assayed glycosidases had the highest activity at pH 8 for both fractions. Soluble fraction of lipase had the highest enzymatic activity at pH 8 in comparison with membrane-bound fraction at pH 10. The soluble fraction showed the highest proteolytic activity at pH 9, while the highest proteolytic activity was observed at pH 8 in the case of the membrane-bound one.