ABSTRACT
Snake neurotoxins that alter the release of transmitter from motor nerve terminals are of considerable scientific and clinical importance and, during the past three decades, their structure and mode of action have been extensively studied. Two kinds of presynaptic neurotoxins have been recognized in the snake venoms: the ß-neurotoxins, which are characterized by the presence of a phospholipase A2 activity and have been found in the venoms of Elapidae, Crotalidae, and Viperidae snakes; and the presynaptic facilitatory neurotoxins, including dendrotoxins, which block a voltage sensitive K+ channel, and the antiacetylcholinesterase toxins or fasciculins. Crotoxin from the South American rattlesnake was the first phospholipase A2 neurotoxin to be purified and crystallized from a snake venom. The first presynaptic pharmacologically characterized toxin was ß-bungarotoxin purified from the venom of the Taiwan banded krait, B. multicinctus. The molecular structure of ß-neurotoxins, therefore, appears very heterogeneous, despite the constant presence of a polypeptide chain homologous with phospholipases A2 from mammalian pancreas and snake venoms.
