THERMOTROPIC CHARACTERISTICS OF PHOSPHOLIPID MIXTURES FROM RBC MEMBRANE

The relationships between membrane function, their physical properties and fatty acid distribution, mainly of the phospholipid fraction received particular attention in these last years. The correlations have been frequently studied analyzing the membrane components and their fatty acids changed in vivo by modification of the diet. With this type of treatment we created a collection of different composition membrane samples from bovine erythrocytes. Aims of this research were: 1) the analysis of phospholipid mixtures extracted from the membranes, 2) the correlation of the composition to the thermotropic properties of the mixtures. Total lipids were extracted from red blood cell (RBC) membranes with chloroform/methanol and the complex lipid mixture was fractionated by column chromatography. The single phospholipid molecular species were resolved by HPTLC and quantitated by scanning densitometry. Fatty acid composition of the phospholipid mixtures was determined by means of gas liquid chromatography and buffered aqueous dispersions of the phospholipids were examined by differential scanning calorimetry. For each sample saturated (S) and unsaturated (U) fatty acid contents as well as unsaturation index (UI) were calculated. Phospholipid samples showed one or two phase transitions at temperatures between 17.7 and 40 °C. The first transition temperature ranged from 17.7 to 26.0 °C. UI and U/S resulted unrelated to the percent content of the different phospholipid molecular species (PC, PE, SM, PS + PI) as well as PC + SM, the predominant constituents of the RBC membrane outer monolayer. A significative linear correlation was found when the first transition temperature was plotted against UI (P< 0,05) and U/S (P< 0,01). The first transition temperature decreased with the increase of UI or of the ratio U/S.