This bird and reptile-specific postsynaptic neurotoxin inhibits the chick muscle alpha-1-beta-1-gamma-delta (CHRNA1-CHRNB1-CHRNG-CHRND) nicotinic acetylcholine receptor (nAChR) 100-fold more compared with the mouse receptor. In vivo, produces rapid flaccid paralysis, dyspnea and increased respiratory rate in geckos. At sublethal doses geckos were immobilized for up to three days and then recovered. Chicks injected with lethal doses showed rapid onset of inactivity, dyspnea and neck droop, and no extended paralysis with survival was seen. Heterodimer of A and B chains; disulfide-linked. Expressed by the venom gland. The measured mass is that of the reduced peptide. LD(50) is 0.55 mg/kg by intraperitoneal injection into geckos. LD(50) is 0.22 mg/kg by intraperitoneal injection into chicks. IC(50) is 11.2 nM for indirectly stimulated, nerve-evoked twitch responses of the chick biventer cervicis muscle acetylcholine receptor channel. Is not toxic to mice at doses up to 25 ug/g (i.p.). Does not inhibit mouse alpha-3-beta-2/CHRNA3-CHRNB2 and alpha-7/CHRNA7 nicotinic acetylcholine receptors. Belongs to the snake three-finger toxin family. Ancestral subfamily. Boigatoxin sub-subfamily.