Purification, characterization of two peptides from Buthus martensi Karch

A new peptide named Martentoxin 1 and an analogue Martentoxin were purified and characterized from the venom of Buthus martensi Karch. Martentoxin 1 consisted of 36 amino acid matrix-residues with molecular mass as 3908.0 Da determined by matrix-assisted laser desorption ionization time-of-flight-MS. The amino acid sequence was determined as GLIDVKCFASSECWTACKKVTGSG QGKCQNNQCRCY by Edman degradation. Martentoxin consisted of 37 amino acid residues with a molecular mass as 4055.3 Da and it showed highly sequence identity to Martentoxin 1 as FGLIDVKCF ASS ECWTACKKVTGSGQGKCQNNQCRCY. Estimation from circular dichroism spectra indicated Martentoxin 1 owned 18.0% alpha-helix, 53.0% beta-sheet structure and 3.9% turn while Martentoxin contained 13.3% alpha-helix, 64.3% beta-sheet structure and 1.1% turn. The toxicity assay showed both peptides had no toxic effects on mice up to the dose of 10 mg/kg. Electrophysiological studies showed that Martentoxin 1 and Martentoxin at the concentration of 1 mum significantly inhibited voltage-dependent Na+ current (I-Na) and voltage-dependent delayed rectifier K+ current (I-K) but had no effects on transient K+ current (I-A). Both interactions with Na+ and K+ channels were irreversible.