Calorimetric Determination of Phospholipid- Melittin Interactions

The effect of melittin incorporated into the phospholipid bilayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at mole fractions up to 3.75 mol% have been investigated. The study reveals a considerable influence of melittin on the phase transition profile and volumetric properties of the DPPC bilayer. The temperature dependence of the coefficient of expansion, , and the volume fluctuations of DPPC – melittin bilayer membranes in their different transition phases were determined by using pressure perturbation calorimetry (PPC), a relatively new and efficient technique, and differential scanning calorimetry (DSC). The experiments were carried out in the temperature range from 10 to 85 °C. Incorporating melittin up to 1.25 mol% into the lipid bilayer abolishes the pretransition. Remarkably, there is no shift in the transition temperature up to 2.5 mol% melittin, while more than one shoulder is observed at the low-temperature side of the DSC peak for 3.75 mol%, and a slight shift in melting temperature,Tm to 32C. This could be linked to the lytic property of melittin at these high peptide concentrations.