Trypsin isolated from the midgut of the tobacco hornworm, Manduca sexta, is inhibited by synthetic pro-peptides in vitro.

The seven residue synthetic peptides VPAYPQR and VPANPQR, identical to the pro-regions of midgut trypsins from Manduca sexta, inhibit the peptidase activity of the mature enzymes. The inhibitory potencies of these peptides towards purified insect trypsin were determined and were found to be more potent at pH 7.0 than at pH 10.0. These peptides did not inhibit porcine trypsin, nor were they degraded rapidly by purified insect trypsin. We suggest that these particular peptides, and insect proregions in general, may be suitable for use in genetically engineered plants as insect specific inhibitors of digestive proteases.