from the venom of the American scorpion Centruroides sculpturatus; reversibly inhibits the current through ERG (ether-à-go-go-related gene) K(+) channels; contains 43 amino acids and has a molecular weight of 4833 Da; amino acid sequence is similar but not identical to that of ergtoxin, a peptide isolated recently from the venom of the Mexican scorpion Centruroides noxius