Practice question

Insect midgut proteases are essential for dietary protein digestion into amino acids required for growth and development. Many Lepidoptera rely predominantly on serine proteases trypsin, chymotrypsin, and elastase active at alkaline pH 10. Proteinase inhibitor genes from plants encode small disulfide-rich proteins that act as pseudo-substrates, tightly occupying enzyme active site forming stable enzyme-inhibitor complex with Ki in nanomolar range. Larvae ingesting inhibitor containing transgenic tissue cannot hydrolyze ingested protein, experience amino acid starvation, upregulate protease synthesis compensating, depleting sulfur amino acids, slowing growth, extending instar duration, and increasing vulnerability to pathogens. Unlike acute toxins, effect is chronic antimetabolic, reducing fecundity. Inhibitor stability in gut critical, with CpTI resisting proteolysis better than soybean inhibitor. Pyramiding with Bt Cry toxins provides complementary modes of action, enhancing durability of insect resistance in cotton and tobacco by simultaneously blocking digestion and permeabilizing midgut epithelium. Compensatory induction of inhibitor-insensitive proteases in insects may reduce efficacy, requiring integration with other control tactics. This antimetabolic concept supports use of proteinase inhibitors in transgenic plants as part of integrated pest management reducing chemical insecticide dependence.