... Gly23 of birtoxin (Fig. 4). In ikitoxin the presence of Glu23 chargepreceding the a-helix modifies the activity of this toxin in aunique way to result in reduced potency in mice. The C-termini of ... previ-ously for birtoxin [6]. Brie y, the cysteine residues of the peptide were reduced and carboxymethylated by incubating in 6Mguanidine hydrochloride, 0.1MTris/HCl (pH 8.3),1mMEDTA and 20 ... analysis, matrix solutions consisting of sinapinic acid, 3,5-dimethoxy-4-hydroxycinnaminic acid,or a-cyano-4-hydroxycinnamic acid, were mixed in a 1 : 1ratiowithsamples,spottedonthetargetandallowedtodry.MASSLYNX(Micromass...