Abstract
The structural and thermotropic properties of alpha-hydroxy fatty acid (HFA) and non-hydroxy fatty acid (NFA) ceramides (CER) have been studied using differential scanning calorimetry (DSC) and X-ray diffraction techniques. The DSC of anhydrous HFA-CER shows a single, sharp reversible transition at 95.6 degrees C (delta H = 15.3 kcal/mol). At intermediate hydrations HFA-CER exhibited more complex behavior but at maximum hydration only a single reversible transition is observed at 80.0 degrees C (delta H = 8.5 kcal/mol). X-ray diffraction of hydrated (74% water) HFA-CER at 20 degrees C shows a lamellar structure with a bilayer periodicity d = 60.7 Angstrum; a single wide angle reflection at 4.2 Angstrum is characteristic of hexagonal chain packing. Above the main transition temperature at 91 degrees C, a hexagonal (HII) phase is observed. In contrast, DSC of anhydrous NFA-CER demonstrates two thermal transitions at 81.3 degrees C (delta H = 6.8 kcal/mol) and 85.9 degrees C (delta H = 3.5 kcal/mol). With increasing hydration, both transitions shift towards lower temperatures; at maximum hydration, on heating, the endothermic transitions occur at 72.7 degrees C (delta H = 9.8 kcal/mol) and 81.1 degrees C (delta H = 4.0 kcal/mol). On cooling, there is hysteresis of both transitions. X-ray diffraction of NFA-CER (80% water) at 20 degrees C shows a well-ordered lamellar structure with a bilayer periodicity d = 58.6 Angstrum and three wide-angle reflections at 4.6 Angstrum, 4.2 Angstrum, and 3.8 Angstrum. At 77 degrees C (between the two transitions), again a lamellar structure exists with reduced bilayer periodicity d = 53.1 Angstrum and four wide-angle reflections at 4.6 Angstrum, 4.2 Angstrum, and 3.8 Angstrum are observed. Above the second transition, only a single low angle reflection at 30.0 Angstrum is observed; a diffuse reflection at 4.6 Angstrum is indicative of a melted chain phase. Thus, HFA-CER exhibits a simple phase behavior involving the reversible conversion of a gel phase to a hexagonal phase (L beta-->HII). However, NFA-CER shows a more complex polymorphic phase behavior involving two gel phases.
Highlights
The structural and thermotropic properties of ahydroxy fatty acid (HFA) and non-hydroxy fatty acid (NFA) ceramides (CER) have been studied using differential scanning calorimetry(DSC)and X-raydiffraction techniques
Ceramide itself is synthesized in the endoplasmic reticulum and transported to the Golgi apparatus where it is converted to cerebroside, ganglioside, or sphingomyelin [9]
Ceramide acts as a precursor for cerebroside, ganglioside, and sphingomyelin, very low levels of free ceramide are found in membranes
Summary
The structural and thermotropic properties of ahydroxy fatty acid (HFA) and non-hydroxy fatty acid (NFA) ceramides (CER) have been studied using differential scanning calorimetry(DSC)and X-raydiffraction techniques. The DSC of anhydrous HFA-CER shows a single, sharp reversible transition at 95.6'C (AH = 15.3 kcal/mol). At intermediate hydrations HFA-CER exhibited more complex behavior but at maximum hydration only a single reversible transition is observed at 8O.O'C (AH = 8.5 kcal/mol). X-ray diffraction of hydrated (74% water) HFA-CER at 20°C shows a lamellar structure with a bilayer periodicity d = 60.7 A; a single wide angle reflection at 4.2 A is characteristic of hexagonal chain packing. X-ray diffraction of NFA-CER (80% water) at 20% shows a well-ordered lamellar structure with a 1 bilayer eriodicity d = 58.6 A and three wide-angle reflections at 4.6 4.2 k,and 3.8 A. Supplementary key words sphingolipids cell signaling second messengers stratum corneum X-ray diffraction scanning calorimetry bilayers phase transitions the exception of sphingomyelin, sphingolipids are usually minor components of membranes. A role for the generated ceramide in mediating some of the activities of these extracellular signals (e.g., tumor necrosis factor-a (TNFa ) , y-interferon or 1-a, 25-dihydroxyvitamin Ds) was demonstrated with the use of water-soluble, cell-permeable ceramide analogues [11, 13, 18, 19].These studies have established a potential signaling pathway involving sphingomyelin hydrolysis with the generation of a puta-
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