Characterization of Insect Proteinases and Their Inhibition by Finger and Little Millet Inhibitors

Abstract

Empirical approach was adopted to examine the interaction of a little and finger millet inhibitors with digestive proteinases of different field and storage pests. Accordingly, gut proteinases of four storage and phytophagous pests were characterized and their inhibition by finger millet (Eluesine coracana Gaertneri) and little millet (Panicum sumatrense Roth) inhibitors has been investigated. The Callosobruchus sp showed acid proteinase with pH optimum of 3.5 and Sitophilus oryzae showed pH optimum of 4.5 apart from their alkaline proteinases with pH 8.5. The proteinases of Tribolium castaneum had wider pH optimum from 5.5 to 8.5. However, all lepidopteran insect proteinases had pH optima ranging from 8.5 to 10.5. The optimum temperature was found to be 30 to 40 °C. The inhibitory activities of little and finger millet inhibitors towards the insect proteinases are very low except notable level inhibition of proteinases of some insects. The gut proteinase zymogram of different insects revealed 2 – 6 isozymes and the inhibitors moderately inhibited all the isozymes of insects tested.