Mechanism of Action of Delta-Enodtoxin fromBacillus Thuringiensis

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Abstract
ABSTRACE The crystalline protein bodies (BB) prcdud by Bacillus thuringiensis consist of a delta-endotoxin having toxicity either for lepidopteran, dipteran, lepidopteran and dipteran, or coleopteran larvae. The delta-endotoxin toxic for lepidopteran or coleopteran larvae consists of two peptides of molecular weight (mol. wt.) 6.5 kilcdaltons (kd). The dipteran-specific deltaendotoxin consists of one peptide of mol. wt. 2.8 kd. The lepidopteran-specific delta-endotoxin acts by causing swelling of midgut cells after ingestion of B B and elevation of the K+ concentration and pH of the hemolymph, in vivo. The cell swelling induced by the toxin is observed only in insect cells but not mammalian cells, in vitro. A proposal for the mechanism of action of the toxin is as follows: the toxin reacts with a receptor on the susceptible cell surface, inducing a cascade of biochemical reactions resulting in stimulation of Na+ influx through Na+ channels, K+ efflux through K+-leak channels arid Na+,K+-pump by Na+,K+-ATPase in the membrane. Due to the net Na+ and K+ influx insect cells swell and burst. In contrast, thedipteran-specific delta-endotoxin has cytolytic activity for insect and mammalian cells, in vitro, and is hemolytic for mammalian erythrocytes, neurotoxic for the cockroach sixth abnoraml ganglion and highly entomccidal for mosquito larvae.

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