Abstract: The secondary structures of melittin and its analogues in Tris buffer, containing 2 mo/L NaCl and 10% hexafluoroisopropanol(HFIP) were determined by CD method. The results showed that melittin and its analogues adopted random coil structures in Tris buffer. The α-helical content of melittin in the buffer containing 2 mol/L NaCl increased markedly, indicating the formation of aggregates, while the analogues did not show a unique conformation. No correlations between the aggregation and antimicrobial or hemolytic activities were found. The α-helical content of melittin and its analogues increased markedly in 10% HFIP, which was widely used to mimic the biomembrane environment in literature, indicating these peptides have an inherent helicity. By comparing the secondary structures and the antimicobial or hemolytic activities, it was found that membranes of bacteria might be a much stronger promoter of α-helical structures than those of erythrocytes and aqueous HFIP, and membranes of erythrocytes has a similar environment with aqueous HFIP.

Key words: Peptide, Melittin, Antimicrobial peptide, Fluorescence, Membrane