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EFFECT OF DISSOLUTION AND DEGRADATION OF BAClLUlS THURlNGIENSlS PARASPORAL CRYSTALS ON TOXICITY TO COTTON BOLLWORM *
Author(s) -
Zhang Jihong,
Wang Chenzhu,
Xiang Xiufen,
Qin Junde
Publication year - 1997
Publication title -
insect science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.991
H-Index - 45
eISSN - 1744-7917
pISSN - 1672-9609
DOI - 10.1111/j.1744-7917.1997.tb00110.x
Subject(s) - proteolysis , toxicity , helicoverpa armigera , trypsin , midgut , dissolution , biology , proteases , bioassay , bacillus thuringiensis , chymotrypsin , incubation , chromatography , food science , biochemistry , enzyme , chemistry , larva , botany , bacteria , organic chemistry , genetics
The effect of dissolution and buffer pH values on the proteolysis of Bacillus thuringiensis subvar. kurstaki HD‐1 parasporal crystals were studied by SDS‐PAGE. Dissolution made crystal much easier to be digested by larval Helicoverpa armigera midgut proteases; the rate of proteolysis of protoxin was faster than that of the crystal. Incubated with larval midgut juice, bovine trypsin and chymotrypsin for 17 h at 30°C, the proteolytic process of crystals deepened as the pH of buffer rose from 6. 9 to 10.5; the complete degradation of crystals occurred at pH 10.5, and the active domains were similar, with molecular weight of 60.5±1.26Kd, 61.6±1.16Kd, and 61.7±2.0Kd respectively. Bioassay results suggested that incubation in alkaline buffer could improve the toxicity of crystals to H. armigera , proteolysis gave no further modification to the toxicity and the toxicity was not significantly different among the products from proteolysis by larval midgut juice, bovine trypsin and chymotrypsin, Whether diets with different pH would affect the toxicity of crystals to H. armiger were also tested. Diets made by 0. 01mol.L ‐1 Tris‐HC1 buffer, pH 8.0 and 0.01mol*L ‐1 glycine‐NaOH buffer, pH 10.0, all significantly increased the toxicity of crystals and no difference between them was observed.