The insecticidal 8-endotoxin produced by Bacillus thuringiensis strain T 84 A1 was found to attack mouse sarcoma 180 ascites cells in vitro, stimulating the release of UV-absorbing substances from the cells into the medium. For this effect it was required that the proteinaceous endotoxin was previously solubilized by gut-juice protease from the silkworm or by a reducing agent. The substances released had a UV-spectrum like that of RNA. Phospholipid was also liberated significantly from sarcoma cells in the presence of solubilized endotoxin. After the midgut of the silkworm, which may be the primary target organ of the toxin, was suspended in a medium containing solubilized toxin, it released significant amounts of UV-absorbing substances into the medium. Similar effects were observed for free cells prepared from the silkworm midgut treated with trypsin. In the latter experiments, however, nonspecific liberation of UV-absorbancy was often observed even in the absence of toxin, suggesting that the intactness of free cells after trypsin-treatment may be critical.
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