Copyright © by Biophysical Society. Final full-text version of the paper available at: http://www.biophysj.org/cgi/content/abstract/88/5/3368
The effects on dielaidoylphosphatidylethanolamine (DEPE) bilayers of ceramides containing different N-acyl
chains have been studied by differential scanning calorimetry small angle x-ray diffraction and 31P-NMR spectroscopy.
N-palmitoyl (Cer16), N-hexanoyl (Cer6), and N-acetyl (Cer2) sphingosines have been used. Both the gel-fluid and the lamellarinverted
hexagonal transitions of DEPE have been examined in the presence of the various ceramides in the 0-25 mol %
concentration range. Pure hydrated ceramides exhibit cooperative endothermic order-disorder transitions at 93 C (Cer16), 60 C
(Cer6), and 54 C (Cer2). In DEPE bilayers, Cer16 does not mix with the phospholipid in the gel phase, giving rise to highmelting
ceramide-rich domains. Cer16 favors the lamellar-hexagonal transition of DEPE, decreasing the transition temperature.
Cer2, on the other hand, is soluble in the gel phase of DEPE, decreasing the gel-fluid and increasing the lamellar-hexagonal
transition temperatures, thus effectively stabilizing the lamellar fluid phase. In addition, Cer2 was peculiar in that no equilibrium
could be reached for the Cer2-DEPE mixture above 60 C, the lamellar-hexagonal transition shifting with time to temperatures
beyond the instrumental range. The properties of Cer6 are intermediate between those of the other two, this ceramide
decreasing both the gel-fluid and lamellar-hexagonal transition temperatures. Temperature-composition diagrams have been
constructed for the mixtures of DEPE with each of the three ceramides. The different behavior of the long- and short-chain
ceramides can be rationalized in terms of their different molecular geometries, Cer16 favoring negative curvature in the
monolayers, thus inverted phases, and the opposite being true of the micelle-forming Cer2. These differences may be at the
origin of the different physiological effects that are sometimes observed for the long- and short-chain ceramides.
This work was supported in part by grants from Ministerio de Educación y
Ciencia (BCM 2002-00784) and Universidad del País Vasco (UPV
00042.310/13552). J. Sot was a predoctoral student supported by the
Basque government.
Peer reviewed