Orthosteric antagonist of the alpha-1A adrenergic receptor (ADRA1A) with an affinity of 0.35 nM (PubMed:20015090). Has also affinity for ADRA1B > ADRA2C > ADRA1D (PubMed:23935897). Acts as a relaxant of smooth muscle. Reduces prostatic muscle tone as efficiently as tamsulosin (an antagonist presently used), but with fewer cardiovascular side effects (PubMed:23005263). Expressed by the venom gland. Due to its high selectivity and potent relaxing effect on isolated prostate smooth muscle, this peptide is in the process of therapeutic development. Does not show interaction with adrenergic receptors (ADRA2A, ADRA2B, ADRA2C, ADRB1, ADRB2), dopaminergic receptors (DRD1, DRD2, DRD3, DRD4, DRD5), histaminic receptors (HRH1, HRH3, HRH4), muscarinic receptors (CHRM1, CHRM2, CHRM3, CHRM4, CHRM5), and serotoninergic receptors (HTR1A, HTR2A, HTR2B, HTR2C, HTR5A, HTR6, HTR7). The mutant AncTx1-W28R-I38S (which is not mutated at position 28 and 38) shows a 10-, 740- and 5-fold increase in inhibition potency than the mutant AncTx1 on alpha-1A, alpha-1D and alpha-2C adrenergic receptors, respectively, but is 2-fold less potent on alpha-1B adrenergic receptor. Is classified as a P-type cytotoxin, since a proline residue stands at position 33 (Pro-31 in standard classification). Belongs to the snake three-finger toxin family. Short-chain subfamily. Aminergic toxin sub-subfamily.