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The impact of three different fabaceous host plants including cowpea (Vigna unguiculata), chickpea (Cicer arietinum), and mung bean (Vigna radiata) seeds was investigated using biochemical approaches on possible changes of gut proteolytic activity of the cowpea weevil, Callosobruchus maculatus at 30±1˚C and 70±5% RH and a photoperiod of 8:16 (L:D). Results revealed that pH of 4-5 and 9 was optimal for the activity of larval gut proteases using azocasein and hemoglobin as general substrates. Different serine (BApNA, SAAPFpNA, PMSF, TLCK, and TPCK) and cysteine (Z-Arg-Arg- pNA, Z-Phe-Arg-pNA and DTT) specific substrates inhibitors and activator were used as a further proof of the proteolytic profile in the gut of C. maculates. Although combinations of serine and cysteine proteases were observed, the cysteine proteases had the highest rate on the studied hosts. The protease activity, especially cystein protease, was the highest on cowpea, which was supported by hemoglobin (0.156±0.045 U mg^-1), Z-Phe-Arg-pNA (2.85 U mg^-1) substrates and DTT (90.00±0.10%) as an activator. Due to the importance and frequency of cysteine proteinases and their effects on biological and physiological process, it would be better to design pest management programs based on cysteine plant proteinase inhibitors as transgenic plants.

Keywords: Chickpea, Cowpea, Cysteine proteinases, digestive enzymes, Mung bean

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