Partial characterization of a chymotrypsin-like protease in the larger grain borer (Prostephanus truncatus (Horn)) in relation to activity of Hyptis suaveolens (L.) trypsin inhibitor

Hyptis suaveolens trypsin inhibitor (HSTI) inhibits, in vitro, most of the trypsin-like serine proteases present in the gut of Prostephanus truncatus (Horn), the larger grain borer. In order to measure its in vivo effectiveness, different doses of the purified HSTI were incorporated into artificial seeds to measure their effects on the growth of P. truncatus larvae and pupae. Results showed that this protease inhibitor had no significant effect in vivo. Consequently, we investigated, identified, and partially characterized an inhibitor-insensitive protease that could explain the growth of P. truncatus on diet containing HSTI. This protease had an apparent molecular mass of 31 kDa, an optimum pH of 7.0, and an activity range extending from pH 6.0 to 8.0, which would allow activity in the gut of P. truncatus. This enzyme could be one of the physiological mechanisms in P. truncatus that allow the species to avoid the adverse effects of trypsin-like protease inhibitors present in the normal diet.