Digestive proteolytic activity in Apodiphus amygdali Germar (Hemiptera: Pentatomidae): effect of endogenous inhibitors

Abstract

The digestive proteolytic profile of <em>Apodiphus amygdali</em> was determined by using several substrates and specific inhibitors. Analysis of optimal pH and temperature showed the highest enzymatic activity at the pH range of 6-7 and temperature of 40°C when azocasein was used as a substrate. By using a negative control, the presence of several specific proteases were determined including tryspin-like, chymotrypsinlike, elastase, cathepsin B, cathepsin L, amino- and carboxypeptidases in the midgut content of <em>A. amygdali</em>, with the highest and the lowest activities of cathepsin L and carboxypeptidase, respectively. pH dependency of specific proteases revealed optimal pHs of 9, 8 and 9 for trypsin-, chymotrypsin-like, 6 for cathepsins and 5-6 for carboxy- and aminopeptidases, respectively. Specific inhibitors, including phenylmethylsulfonyl fluoride, Na-p-tosyl-L-lysine chloromethyl ketone, Ntosyl- L-phenylalanine chloromethyl ketone, L-trans-epoxysuccinylleucylamido-(4-guanidino)-butane, phenanthroline and ethylendiamidetetraacetic acid, significantly decreased proteolytic activity, indicating the presence of different proteases in the midgut of <em>A. amygdali</em>. Extracted inhibitors from the midgut demonstrated significant inhibition of specific proteolytic activities of <em>A. amygdali</em> except for cathepsin B and aminopeptidase. The results indicated that determination of digestive proteolytic activity could be helpful to clarify digestion process in insects. Moreover, understanding the nature of digestive proteases might be used to develop several inhibitors for providing resistant crop varieties against pests.

Ontogenic development of the digestive enzymes and chemical composition of Hermetia illucens larvae of different ages

“…Variations in the optimal pH of general proteolytic activity in insects could be attributed to feeding habit and whether they are monophagous or polyphagous. Given that polyphagous insects feed on various hosts, the variability in pH for proteases could be attributed to the host materials or secondary metabolites of plants fed upon (Ramzi & Zibaee, 2014).…”