Toxins from Crotalus durissus terrificus venom

Phospholipase A, crotapotin and crotamine were purified from the venom of crotalus durissus terrificus. Molecular weigths were respectively estimated in 13400, 8300 and 4880. By sephadex gel filtration, stable complex is formed by interaction (1:1 molar ratio) of Phospholipase A (LD=0,55mg/Kg, in mice) and crotapotin, obtaining an increase in the toxicity of Phospholipase A in 10 fold to LD50=0,05mg/Kg. These facts indicate crotoxin as a product of 1:1 molar ratio interaction of crotapotin and Phospholipase A. By sephadex gel filtration an unstable complex is formed by interaction of crotapotin and crotamine (LD50=0,8mg/Kg, in mice), increasing the toxicity of crotamine approximately 4 fold to LD50=0,2mg/Kg. In tritium-hydrogen exchange experiments, the back exchange kinetic of these tritium labelled proteins were measured in gel filtration columns of sephadex G 25 'coarse' showing for Phospholipase A two clearly distinguishable kinetic classes of exchangeable hydrogens. From the exchangeable hydrogens only 68% were rapidly exchanged and the occurrence of hydrogens envolved in alpha-helix was practically absent. Crotapotin has no hydrogens of alpha-helix and 83% of exchangeable hydrogens were rapidly exchanged with solvent. Crotamine, after a initial heating in tritiated water showed that 31% of exchangeable hydrogens were slowly exchanged with solvent. After 18 hours of heating, that number diminished for 11%. Crotoxin showed three exponential classes of exchangeable hydrogens and about 26 protons have alpha-helix characteristic exchange rate. A possible conformational change after Phospholipase A - crotapotin interaction is suggested. (Author)