Mastoparan B (MP-B)
, an umphiphilic a-helical peptide newly isolated,from the hornet Vespa basalis, was studied in comparison with mastoparan ( M P ) , in terms of interaction with the phospholipid bilayer and of' hemolytic and antimicrobial activity. The amphiphilic structure of MP-B has more hydrophilic amino acid residues in the hydrophilic surface than that of MP.
Although each peptide had a considerubly different effect on the interaction with lipid bilayers (e.g., lheir conformation in the presence of acidic and of neutral lipids and dye-release ability jrom the encapsiilated liposomes), on the whole the interaction mode was similar. MP-B caused a change in the shape of erythrocytes from normal discoid to a crenated ,form (named echinocytes) . M P exhibited strong activity against gram-positive bacteria but not against gramnegative ones. Contrary to this, MP-B showed both strong activity against gram-positive bacteria and potent activity against gram-negative bacteria. Whereas both peptides have almost the same residues on the hydrophobic side, the difference in the hydrophilic surface area on the molecules seems t o lead to the subtle change in its interaction with membranes, resulting in the alteration of biological activity.