Determination of digestive proteolytic profile in the larvae of Dyspessa palidata (Staudinger) (Lepidoptera: Cossidae)

Abstract

Digestive proteolytic profile was determined in the larvae of <em>Dyspessa palidata</em> (Staudinger), which is the most important pest of Alliaceae in Europe and Iran. Compartmentalisation of the proteolytic activities by considering soluble and membrane-bound fractions revealed that soluble fractions of the whole midgut preparations had higher general proteolytic activity than membrane-bound fractions. Also, four proteolytic bands were observed in the soluble fraction of the total midgut preparation in electrophoresis. Compartmentalisation of the specific proteases revealed presence of trypsin, elastase, aminoand carboxy peptidases in posterior midgut but the highest activities of other proteases were found in anterior midgut. The highest activity of general protease was found at pHs of 6 and 8. Also, pH dependency of trypsin, chymotrypsin and elastase were found at values of 8, 7-8 and 9 but cathepsins had the optimal pH at 6. Exopeptidases showed the optimal value at pH of 7 although carboxypeptidase showed same activity at values of 6 and 7. The inhibitory concentrations 50% (IC<sub>50</sub>) of AEBSF.HCL on trypsin, chymotrypsin and elastase proteases were found to be 3.69, 3.31 and 4.09 mM, respectively. IC<sub>50</sub> concentrations of TLCK, SBTI and TPCK significantly inhibited trypsin and chymotrypsin activities. IC<sub>50</sub> of E-64 were 3.67 and 4.16 mM on cathepsin B and L but cystatin revealed 5.22 and 4.48 mM concentrations on cathepsin B and L, respectively. EDTA and phenathroline as metalloproteinase inhibitors had IC<sub>50</sub> of 3.25 and 3.91 mM on general proteolytic activity. Results of the current study revealed larvae of <em>D. palidata</em> utilised different proteases to increase digestive efficiency when they fed on the host plants containing several toxic molecules.