Some articles on contryphans:

... The contryphans (conus + tryptophan) are a family of peptides that are active constituents of the poisonous venom produced by cone snail (genus conus) ... The two amino acid cysteine residues in contryphans are linked by a disulfide bond ... In addition, contryphans undergo an unusual degree of post-translational modification including epimerization of leucine and tryptophan, tryptophan bromination, amidation of the C-terminus ...