INHIBITION OF DIGESTIVE TRYPSIN-LIKE PROTEASES FROM LARVAE OF SEVERALLEPIDOPTERAN SPECIES BY THE DIAGNOSTIC CYSTEINE PROTEASE INHIBITOR E-64

The cysteine proteinase inhibitor, E-64, inhibited the hydrolysis of t hree commonly used trypsin synthetic substrates (BApNa, BAEE and TAME) and two protein substrates (azocasein and azoalbumin) by digestive tr ypsin-like proteinases from several lepidopteran larvae, despite the i nhibitor's assumed complete specificity for cysteine proteinases. Ther e were differences in susceptibility among trypsin-like proteinases fr om different species, and within a given species depending on the subs trate used in the assay, In general, BApNa hydrolysis was more suscept ible to the action of E-64 than any of the other substrates, Furthermo re, commercial bovine trypsin was inhibited by E-64 when BApNa and azo albumin were used as substrate, but E-64 failed to inhibit BAEE, TAME and azoalbumin hydrolyses. Kinetic analysis of the inhibition with E-6 4 of BApNa hydrolysis by Ostrinia nubilalis midgut extracts indicates a reversible competitive mechanism, The significance of our results ar e discussed, particularly from the point of view of the characterizati on of insect proteases, since E-64 is broadly used as a diagnostic too l for the identification of cysteine proteinases. (C) 1997 Published b y Elsevier Science Ltd.