Bibrotoxin, a novel member of the endothelin/sarafotoxin peptide family, from the venom of the burrowing asp Atractaspis bibroni

Abstract A new member of the endothelin/sarafotoxin family of vasoconstrictor peptides, bibrotoxin (BTX), was isolated from the venom of the burrowing asp Atractaspis bibroni by reversed-phase FPLC. The amino acid sequence of BTX differs from SRTX-b in the substitution Ala 4 instead of Lys 4 , which suggests that it represents the peptide isoform of Atractaspis bibroni corresponding to SRTX-b. BTX competed for [ 125 I]ET-1 binding to human ET B -type receptor with a K i of 3.2 × 10 −9 M compared to 4.2 × 10 −9 M for SRTX-b. In rat thorax aorta BTX induced vasoconstrictions with a threshold concentration of 3 × 10 −8 M compared to 1 × 10 −9 for ET-1.