Interferes with neuromuscular transmission by inhibiting the enzyme acetylcholinesterase (AChE) present at the neuromuscular junction. It selectively binds and inhibits with a 1:1 stoichiometry the mammalian and electric fish AChE at picomolar concentrations. It is highly specific for the peripheral site of AChE and blocks the entry of acetylcholine into the active site of the enzyme (through the Met-33 residue), thereby preventing its breakdown. It has been called fasciculin since after injection into mice it causes severe, generalized and long-lasting (5-7 hours) fasciculations. Expressed by the venom gland. LD(50) is >20 mg/kg by intravenous injection. Belongs to the snake three-finger toxin family. Short-chain subfamily. Acn-esterase inhibitor sub-subfamily.