Canadian Journal of Pure & Applied Sciences

Abstract: The effect of melittin at mole fractions of up to 3.75mol%, on the dynamic and mechanical properties of 1,2-dipalmitoylsn- glycero-3-phosphatidylcholine (DPPC) was investigated using ultrasound velocimetry and densitometry. The isothermal compressibility and volume fluctuations of DPPC – melittin bilayer membrane in their different transition phases were determined. At the melting temperature, Tm, a general increase in velocity number [u] as compared to the pure lipid was noticed. However, at 3.75 mol%, melittin displays the broadest peak and lowest value of [u] compared to the other melittin concentrations, which could be linked to the lytic property of melittin at high peptide concentrations. The melittin concentration effects on the partial specific volume, ?o and the adiabatic compressibility coefficient of the lipid, ?S lipid of the DPPC bilayer reveals a slight shift of the main transition to lower temperature and a continuous decrease in ?o with concentration increase above the Tm (except between 1 and 1.25%), as well as a decrease in ?S lipid with decrease in melittin concentration. Again, the isothermal compressibility peak at the main transition drops drastically upon addition of melittin at concentrations as low as 1 mol% and then increases with increase in melittin concentration. At all melittin concentrations, ?T lipid is greater than ?S lipid in the gel-fluid region by ? 20%. The maximum value of the relative volume fluctuations of 12 % is reached for DPPC at the main transition, and is strongly dampened upon addition of melittin. Only a slight decrease in the calculated relative volume fluctuations with melittin concentration is observed between concentrations 0 and 1.0 mol%.