Serine protease inhibitors (PIs) have been described in many plant species
and are universal throughout the plant kingdom, where trypsin inhibitors
is the most common type. In the present study, trypsin and chymotrypsin
inhibitory activity was detected in the seed flour extracts of 13 selected
cultivars/accessions of cowpea. Two cowpea cultivars, Cream7 and Buff,
were found to have higher trypsin and chymotrypsin inhibitory potential
compared to other tested cultivars for which they have been selected for
further purification studies using ammonium sulfate fractionation and
DEAE-Sephadex A-25 column. Cream7-purified proteins showed two bands
on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE)
corresponding to molecular mass of 17.10 and 14.90 kDa, while the
purified protein from Buff cultivar showed a single band corresponding
mass of 16.50 kDa. The purified inhibitors were stable at temperature
below 60°C and were active at wide range of pH from 2 to 12. The kinetic
analysis revealed noncompetitive type of inhibition for both inhibitors
against both enzymes. The inhibitor constant (Ki) values suggested high
affinity between inhibitors and enzymes. Purified inhibitors were found to
have deep and negative effects on the mean larval weight, larval mortality,
PI was more effective than Cream7 PI. It may be concluded that cowpea PI
gene(s) could be potential insect control protein for future studies in
developing insect-resistant transgenic plants.pupation, and mean pupal weight of Spodoptera littoralis, where Buff