A novel protease inhibitor was isolated and purified from the mature seeds of jackfruit (Artocarpus heterophyllus) by precipitation with ammonium sulphate, followed by DEAE-cellulose and gel filtration (Sephadex G-100) chromatography. The isolated protease inhibitor strongly inhibited papain and midgut proteases of yellow stem borer (Scipophaga incertulas) larvae, as seen by in vitro assay. The purified protease inhibitor was active over a wide range of pH with the maximum activity between pH 4 and 10. This protein was also stable up to 80°C, but the retained activity was lost at 100°C, when heated for 30 min. The molecular mass of the purified cysteine-like protease inhibitor is to be 14.50 kDa as determined by SDS-PAGE. Significant reduction in larval weight and mortality was observed, when fresh rice culms with protease inhibitor was feeded to the yellow stem borer larvae. These results may provide important information to control the yellow stem borer in rice with respect to naturally occurring insecticidal proteins. The observed differences would potentially translate into reductions in population growth of yellow stem borer, indicating a potential value of using jackfruit protease inhibitor for protecting rice plants against damage by the yellow stem borer.
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