Effects of the Three Proteases from Gut Juice of the Silkworm,Bombyx mori, on the Two Morphologically Different Inclusions of δ-Endotoxin Produced byBacillus thuringiensis kurstakiHD-1 Strain

Abstract

Three proteases designated P-I, P-II, and P-III were separated from larval gut juice of the silkworm, Bombyx mori, and the effects of these proteases on the two morphologically different inclusions produced by Bacillus thuringiensis kurstaki HD-1 strain were investigated. Bipyramidal inclusions were solubilized by each protease at pH 10.2, and proteins with a molecular weight of about 60,000 were produced, while cuboidal inclusions were resistant to the proteases. Protease P- III appeared to be most important in the dissolution of the bipyramidal inclusions. Based on the affinity to various synthesized substrates, P-III was considered to be a chymotrypsin-like protease. After dissolution of inclusions by P-III, dissolved and undissolved fractions were separated, and the insecticidal activity of each fraction was tested. Results indicate that bipyramidal inclusions are preferentially toxic to the silkworm and the cuboidal ones carry the mosquitocidal activity.