Penetrability of proteins through the digestive system of Sarcophaga falculata blowfly

On the background of the previous findings concerning the passage of a low molecular basic protein from cobra snake venom through the gut of a blowfly (Primor, N., Teitelbaum, Z. and Zlotkin, E. (1980) Biochim, Biophys, Acta 627, 71--81) several additional proteins were tested in the present study. With the aid of toxicity tests, radioiodinated proteins, gel filtration chromatography, and the usage of Sarcophaga falculata flies as test animals, the following information was obtained: 1. Out of the five species (representing four orders) of insects tested, only flies demonstrated the lethality by oral application of cobra snake venom. 2. The absence of oral toxicity of flies to phospholipase A2 (highly lethan by injection of cobra venom with molecular weight of about 13,000) was due to its impermeability through the digestive system. 3. About 2.2% of the orally applied low molecular weight basic neurotoxin (Mr 7000) from cobra venom crossed the gut and was found in the insects' hemolymph. 4. Bovine serum albumin (Mr 68,000) and an immunoglobulin (Mr 180,000), under the present experimental conditions, were found to be gut impermeable.