[Interaction of melittin with a model membrane in the presence of antibodies].

The method of fluorescence spectrofluorimetry has been applied to study the interaction of melittin at high and low ionic strength with the phosphatidylcholine model membrane in the presence of monospecific polyclonal and monoclonal antibodies against this peptide. The formation of antigen-antibody complex with the excess of the antigen is shown to decrease the leakage of calcein, a fluorescence dye. With the excess of antibodies the dye leakage is completely suppressed.

[Determination of melittin antigenic determinants in a model membrane].

Monospecific polyclonal antibodies labelled with colloid gold were obtained against melittin in different conformations (monomer, tetramer and complex with BSA). They were used for electron analysis of the position of antigenic determinants of melittin in DMPC model membrane. The antibodies reacted in cross-immunoassay in different titres with all antigenes and this evidences for the presence of common antigenic determinants in their structures.

[The effect of anions on the hemolytic activity of melittin].

Anions causing the melittin aggregation in the solution are shown to slow down the lytic process not preventing it completely. The equalization of the oncotic gradient through the erythrocytic membrane by the addition of polyethylene glycols of different molecular weight into the extracellular medium made it possible to establish the colloid-osmotic mechanism of hemolysis and to estimate the diameter of melittin pores. The diameter depends on the polypeptide concentration and makes up 20-30 A with its content of (6 divided by 12).

[Ionic selectivity of melittin-modified flat lipid bilayers].

It has been established in experiments with the bilayer lipid membranes (BLM) that at pH greater than 6.6 the melittin pores are cation-selective and at lower pH they are more selective by anions. The property of melittin pores is shown to be provided by the amino group of the N-terminal glycine residue.

[Interaction of melittin with model membranes: effect on the size and permeability of liposomes].

The influence of melittin, a monomer devoid of the phospholipase activity, on the size and permeability of liposomes from egg lecithin (PC), dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) has been investigated by the methods of fluorescence spectroscopy, quasi-elastic light scattering and freeze-fracture electron microscopy. While studying calcein release from liposomes under the influence of melittin it has been shown that binding of melittin with a bilayer is a fast process which depends on the concentration lipid: protein (Ri) ratio as well as on the phase state of the lipid. The lipids being in the liquid-crystalline forms (PC and DMPC) are characterized by a more rapid release of the dye-stuff from liposomes than DPPC vesicles being in gel state with the same Ri.