toxin-iii-(anemonia-sulcata) and acetic-anhydride

The effect of modification of amino groups on RTX-III induced lethality in mice has been studied. The toxicity was not affected by guanidination of one or two lysine residues with O-methylisourea, but guanidination of three or four lysine residues decreased lethality two-fold. Acetylation of the N-terminal amino group with [3H]acetic anhydride caused a 12-fold decrease of lethality. The toxin containing acetylated Lys-4 or one of three C-terminal lysine residues had half the lethal potency of the native RTX-III. Diacetylated derivatives were 30- to 35-fold less toxic than the native toxin. By circular dichroism, it was shown that modification of one or two amino groups did not affect the secondary structure of the toxin. We conclude that protonated amino groups are essential for neurotoxicity.

Topics: Acetic Anhydrides; Acetylation; Amino Acid Sequence; Amino Acids; Animals; Chromatography, High Pressure Liquid; Chromatography, Ion Exchange; Circular Dichroism; Cnidarian Venoms; Male; Methylurea Compounds; Mice; Mice, Inbred BALB C; Molecular Sequence Data; Peptide Mapping; Protein Conformation; Sea Anemones; Structure-Activity Relationship; Trypsin