Isolation, purification and N-terminal sequencing of a bioactive peptide that alters action potentials from the venom of Buthus martensii Karsch

A bioactive peptide that extensively prolongs action potentials (APs) in frog nerve has been isolated and purified from the venom of the scorpion Buthus martensii Karsch (BMK). The peptide, designated as BMK 18(2), was purified using gel filtration, ion exchange, FPLC, and HPLC chromatography. APs recorded in the presence of nanomolar concentrations of the peptide were extensively prolonged with some attenuation in their heights. The N-terminal sequence of BMK 18(2) was found to be: VRDAYIAEDYD-VYH-ARDA. Sequence similarity comparisons to other alpha -scorpion toxins suggest that the two blanks in the sequences are cysteines. The molecular weight (M.W.) of BMK 18(2) was determined by LC/MS/MS to be 7185 Da. Since the peptide prolongs APs when both K+ and Ca++ channels were blocked and shows sequence similarity to other alpha -neurotoxins, it appears likely that BMK 18(2) acts to alter Na channel inactivation to produce its effect.