A 22-residue peptide toxin from the venomous marine snail Conus geographus (L.) was found to have a most unusual amino acid composition: Lys4, Arg3, 1 2 Cys 6 , Asx2, Glx2, Thr, Ala, plus three residues of trans-4-hydroxyproline. Absence of Gly and Pro indicates that the hydroxyproline must be in sequences different from those in which hydroxyproline occurs in collagen and other proteins.
