In vivo and in vitro inhibition of Spodoptera littoralis gut-serine protease by protease inhibitors isolated from maize and sorghum seeds.

Seeds of cereals (Gramineae) are a rich source of serine proteinase inhibitors of most of the several inhibitor families. In the present study, trypsin and chymotrypsin inhibitory activities was detected in the seed flour extracts of three varieties of maize (Zea maize) and six varieties of sorghum (Sorghum bicolor). The maize variety, Hi Teck 2031 and the sorghum variety, Giza 10 were found to have higher trypsin and chymotrypsin inhibitory potentials compared to other tested varieties for which they have been selected for further purification studies using ammonium sulfate fractionation and DEAE-Sephadex A-25 column. Maize and sorghum purified proteins showed a single band on SDS-PAGE corresponding to molecular mass of 20.0 and 15.2 kDa for maize and sorghum PIs respectively. The purified inhibitors were stable at temperature below 60 °C and were active at wide range of pH from 2 to 12 pH. The kinetic analysis revealed non-competitive 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, pupation and mean pupal weight of S.littoralis where maize PI was more effective than sorghum PI. It may be concluded that maize and sorghum protease inhibitor gene(s) could be potential targets for future studies in developing insect resistant transgenic plants.