Quantification of 2-disulfide bonded isomers of apamin, a peptidic toxin, leads to the observation of a structural rearrangement

Apamin (APA1) interacts strongly with SK channels and blocks corresponding SK currents. Apamin is an octadecapeptide with four cysteine residues assembled in two disulfide bridges. In the context of our program related to the development of selective blockers of SK channels, we were interested in assessing the biological activity of two isomers of apamin (APA2 and APA3). These peptides present another disulfide bond connectivity. These peptides were produced by chemical synthesis. Before these biological evaluations, the quantification of peptide content in our samples was needed. Thus, solution of these peptides were analyzed by NMR techniques.