The mechanism of an anti-toxin protein isolated from the serum of the South American rattlesnake (Crotalus durissus terrificus) that neutralizes both lethal and phospholipase A2 activity of crotoxin from its venom of the same snake was investigated. The ant-toxin was shown to form a stable complex with the toxin by dissociating the acidic protein from its basic phospholipase A2 component of the toxin. The protein structure of the anti-toxin was elucidated by protein and DNA sequencing of cDNA clones. The amino acid sequence of the anti-toxin indicates that it is an acidic protein. It forms an octamer in solution and binds 8 moles per mole of toxin.
