Glucosylceramides of oat root plasma membranes--physicochemical behaviour in natural and in model systems

Glucosylceramides from oat root plasma membranes have been characterized using HPLC-particle beam-mass spectrometry, differential scanning calorimetry, low angle X-ray diffraction and surface balance technique. 24:1-OH was dominating fatty acid (90%) together with 24:0-OH and 22:1-OH. The sphingosine base was sphingadienine isomers and the monosaccharide alpha and beta glucose. Differential scanning calorimetry of an aqueous dispersion of glucosylceramide revealed during heating an endothermic gel-liquid crystalline transition with double peaks at 47 degrees and 51 degrees C, the lowest known for naturally occurring glucosylceramides. A cooling scan after the endothermic gel-liquid transition showed one exotherm at 15 degrees C and if this was followed by another heating scan a large exotherm appeared with a peak at 18 degrees C. During the second heating the matrix was hydrated and the exotherm at 18 degrees C reflects then the transition between the supercooled metastable gel phase and the corresponding hydrated form. The calorimetric data indicate a lamellar phase which during the cooling scan appeared as an supercooled liquid crystalline phase. Low angle X-ray diffraction confirmed these calorimetric data. The surface pressure-area-curves of pure oat glucosylceramides were more expanded than those of bovine origin. Mixtures of oat glucosylceramides and phosphatidylcholine species similar to those present in oat root plasma membranes showed molecular miscibility but no interaction.