ISOLATION AND CHARACTERIZATION OF A POTENT CURARIZING POLYPEPTIDE FROM TITYUS DISCREPANS SCORPION-VENOM

The pure TdI-1 polypeptide that blocks miniature endplate potentials ( MEPPs) and abolishes or reduces endplate potentials (EPPs) below the a ction potential threshold was identified from the crude fraction of Ti tyus discrepans venom. The toxin is a potent reversible non-depolarizi ng muscle relaxant that blocks more than 95% of the EPP at a 2 mu M (0 .1 mg/ml) concentration. On a molar basis, TdI-1 is as potent as or mo re potent than many muscle relaxants since, at the concentration used, the toxin suppressed more than 95% of the EPP, Using matrix-assisted laser desorption time of flight (MALD-TOF) ionization mass spectrometr y, TdI-1 was found to have an unsually large mel. wt for a scorpion to xin, close to 48,000. The N-terminal sequence of the first 23 residues of TdI-1 was also determined. The fragment differs from the N-termina l sequences of all 140 peptidic scorpion toxins found in the SWISSPROT and PIR databases using the search engine of the felix.EMBL-Heidelber g.de computer (European Molecular Biology Laboratory, Heidelberg, Germ any). (C) 1997 Elsevier Science Ltd.