Differences in ion-channel formation by ampullosporins B, C, D and semisynthetic desacetyltryptophanyl ampullosporin A

Peptaibol-type ampullosporins B (2) and D (4) are capable of forming ion-conducting pores in planar lipid bilayer membrane prepared from soybean phosphatidylcholine in a similar manner as it was shown for ampullosporin A (1). However, the isomeric ampullosporin C (3) was required in 20-fold higher concentration to afford a comparable effect. In contrast to 1, 2, 3 and 4, the desacetyltryptophanyl ampullosporin A (5) failed to form ion channels. The results suggest that the sequence of amino acids especially at positions 8–10, the nitrogen-terminal acetyl residues and tryptophane are major factors determining ion-channel formation within bilayer membranes. The differences in membrane activities were comparable to the observed biological activities.