Partial Physicochemical and Kinetic Characterization of Tomato Plant Protease Inhibitors and Proteases from the Cotton Leaf Worm, Spodoptera littoralis (Boisd). (Noctuidae: Lepidoptera)

Proteins inhibiting proteases extracted from tomato plant leaves and the attacked gut proteases from the cotton leaf worm, Spodopiera littoralis (Boisd.) were characterized in some of their physicochemical and kinetic properties. The inhibition on proteases by the tomato plant protease inhibitors (PIs) crude extract protein was stable at pH range 6-11,temperature of 80 degrees C and had a Ki value of 19.6x10(-6) M, and IC50 value of 21x10(-9) mole protein ml(-1), with a competitive inhibition mechanism. Activity of gut proteases from the 4th larval instar of S. littoralis towards bovine serum albumin as a substrate revealed that the optimum temperature was 55 degrees C, and pH was 8.5 suggested that the larvae used serine proteases to digest proteins. A period of 10 min for S. littoralis larval gut proteases was found to fit well within the linear part of enzyme activity curve and hydrolysis had a linear dependence on the substrate concentration from 10(-7) to 10(-6) where the peak is reached. Using Lineweaver-Burk plot, K-m of larval proteases catalyzed reactions was 25x 10(-8)M and V-max was 142 n mole D, L alanine/min/gut. The high degree of tomato leaves Pis stability either to temperature or pH, and low inhibition kinetic values might be of a significant importance in the field of insect control.