PHYSICAL STUDIES OF MYELIN .I. THERMAL ANALYSIS

1. 1. Myelin isolated from ox brain white matter and the lipids extracted from this material have been examined by thermal analysis techniques including differential thermal analysis and differential scanning calorimetry. The results provide information about the organisation of lipids and water in the myelin structure. 2. 2. On drying myelin a crystallisation and precipitation of the lipid and the cholesterol takes place. Endothermic transitions associated with the lipid and cholesterol can then be observed. 3. 3. The total lipid extract in water does not show a detectable endothermic transition but the cholesterol-free lipid does. In the absence of cholesterol, part of the myelin lipid is crystalline at body temperature. 4. 4. With wet myelin no thermal transitions are detectable. In this case the lipids and cholesterol appear to be organised into a single phase. The presence and organisation of the cholesterol in the membrane appear to prevent the lipids from crystallising. 5. 5. To maintain the organisation of the lipid in the myelin there appears to be a critical amount of water required. This water is unfreezable at 0° and may correspond to bound" water. © 1968."