Differential scanning calorimetry of erythrocyte reconstituted membrane

The thermal properties of biomembranes examined by dífferential calorimetry mimic the properties of bílayers formed from their isolated lipids or from synthetic lipids. In this study we have analyzed, by differential scanning calorimetry (DSC), the thermal behaviour of lipids extracted from bovine erythrocyte and of their reconstítuted mixtures. Membrane lipids were extracted from blood samples of 11 cows and separated in the three components: cholesterol, phospholipids and glycolipids. Phospholipid and glycolipid classes were determined by thin layer chromatography. Lipids from erythrocyte membrane of different animals (at controlled diet), at a given time, were pooled together at a proportional amount like in the original membranes. DSC was performed on aqueous buffer dispersions (pH 7.4) of the average lipid components but, ín some cases, the sample contained lipids ísolated from one animal. Average phospholipid sample exhibited two phase transitions: the first at 24 - 26 °C and the second at about 38 °C. Some scans of phospholípids from one animal show only the first transítíon which occurs between 23.1 and 25.4 °C whereas the second phase transition, when occurring, is at very different temperatures (32.4 - 38.1 °C). For all average glycolipid samples one transition was observed at about 35 °C. Mixtures of cholesterol and phospholipids show only one broad transition. In these míxtures the transition temperature is close to that of the second transition of phospholipid samples. Some correlations between the transition temperatures and the amounts of different phospholipids in the samples have been tested but it seems important to consider the fatty acid composition of the studied míxtures to account for the different levels of saturated and unsaturated fatty acids.