Toxic Mastoparan B(MP-B) which is purified from the venom of the hornet Vespa basalis is a cationic amphiphilic tetradecapeptide. MP-B and its Ala-substituted analogues were synthesized by solid phase method and the toxic peptide-membrane interactions were examined by circular dichroism(CD) spectra, fluorescence spectra, and leakage abilities in phospholipid membranes. In the presence of phospholipid vesicles, synthetic MP-B and its analogues formed amphiphilic α-helical structures, but in the buffer solution, those exhibited random coil conformation as measured by CD. Fluorescence spectra of MP-13 and its analogues which indicated the binding affinity of peptide on phospholipid vesicles showed that the replacement of Lys at position 2 and 11 with Ala caused a remarkable effect in the blue shift and that at position 2, in the leakage ability of the peptide.

Toxic peptides from hornet venom, mastoparan and mastoparan-B were synthesized using the solid phase peptide synthesis method and investigated the interaction of them with phospholipid bilayer, antibacterial activity, and hemolytic activity. Both toxic peptides could induce dye release at a low concentration in neutral liposome. The binding affinity of mastoparan-B for neutral liposome was smaller than that for acidic one. Mastoparan and mastoparan-B had strong antibacterial activity for gram-positive bacteria, but weak or potent activity for gram-negative ones, respectively. Mastoparan and mastoparan-B lysed erythrocyte very little up to 5 μM.