This study examined how cationic α‑helical antimicrobial peptides such as protamine exchange between the aqueous phase and the transmembrane β‑barrel porin OmpF ( E. coli ) at the single‑molecule level. High‑resolution conductance recordings in planar lipid bilayers revealed clear voltage‑ and concentration‑dependent ion current blockages, consistent with transient peptide interactions within the OmpF lumen. Peptide length inf...