Neuromuscular blocking activity of two fractions isolated from the venom of the seasnake, Laticauda semifasciata

Two components (0·06 M and 0·09 M fractions) have been isolated from the venom of the seasnake, Laticauda semifasciata. Both are similar polypeptides, each with about 100 amino acids and a mol. wt of approximately 10,000. When tested on the isolated chick biventer cervicis nerve-muscle preparation, both fractions were post-junctional cholinoceptor antagonists, although about 100 times less active than erabutoxin b from the same venom. The fractions chemically resemble venom phospholipase A, but they differed from the enzyme in some effects at the neuromuscular junction. The fractions were very slowly and only partially reversible, whereas the effects of phospholipase A were reversed rapidly on washing.