Immunochemistry of scorpion alpha-toxins: antigenic homologies checked with radioimmunoassays (RIA).

Three toxins, i.e. toxins II and III of Androctonus australis Hector and toxin I of Buthus occitanus tunetanus, were labeled with 125I. High specific radioactivities were obtained (490-1100 Ci/mmole) that allowed the setting up of three radioimmunoassays. We were able to quantify the amount of toxin in 0.1 ml of 10(-9)-10(-10) M solutions and to test antigenic homologies between toxins belonging to different structural groups. Three possibilities exist: (1) no cross-reactivity when sequence difference is greater than 25%; (2) full cross-reactivity when this difference is lower than 25%; (3) partial cross-reactivity, which is interpreted as a loss of some common antigenic sites.