Allosteric modulator of the GABA(A) receptor (GABR), possibly increasing receptor affinity for the agonist, thus enhancing receptor opening and macroscopic desensitization. In vivo, intracerebroventricular injection into mice results in periods of reduced basal activity, followed by bursts of intense seizures and death. Expressed by the venom gland. LD(50) is 0.01 mg/kg by intracerebroventricular injection in mice. Does not bind to nicotinic acetylcholine receptors (nAChR), muscarinic acetylcholine receptors (mAChR), acetylcholinesterase (AChE) or to receptors for glycine and glutamate. Belongs to the snake three-finger toxin family. Ancestral subfamily.