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.