TY - JOUR
T1 - Acyl Chain Order and Lateral Domain Formation in Mixed Phosphatidylcholine-Sphingomyelin Multilamellar and Unilamellar Vesicles
AU - Lentz, Barry R.
AU - Hoechli, Mathias
AU - Barenholz, Yecheskael
PY - 1981/11
Y1 - 1981/11
N2 - The phase behavior of mixtures of dimyristoylphosphatidylcholine (DMPC) with V-palmitoylsphingosinephosphorylcholine (C16SPH) has been investigated in both small unilamellar and large multilamellar vesicles. The steady-state fluorescence polarization of 1,6-diphenyl-1,3,5- hexatriene (DPH) has been used to detect temperature-induced structural changes in these membranes. In addition, electron microscopy has revealed vastly different fracture-face morphologies for large multilamellar vesicles “jet-frozen” from different temperatures. These data have been iriterpreted in terms of proposed phase diagrams for this lipid mixture. The shapes of the proposed phase diagrams have led us to conclude that phosphatidylcholine and sphingomyelin species of similar acyl chain length mix freely in both highly curved and uncurved bilayers, except at temperatures at which both lipids are in low-temperature, ordered phases. In addition, the similarity of these phase diagrams to phase diagrams for analogous mixtures of pure phosphatidylcholines suggested that sphingomyelin and phosphatidylcholine species might substitute for each other in supporting the lamellar phase necessary to cell membrane structure. Finally, the anisotropy of DPH fluorescence was found to be essentially invariant with sphingomyelin content at temperatures just above and below the solid-liquid phase separation in small unilamellar vesicles. This demonstrates that the sphingomyelin backbone, per se, does not order the membrane bilayer. These results are discussed in terms of the possible role of sphingomyelin in controlling acyl chain order withiri mammalian cell membranes.
AB - The phase behavior of mixtures of dimyristoylphosphatidylcholine (DMPC) with V-palmitoylsphingosinephosphorylcholine (C16SPH) has been investigated in both small unilamellar and large multilamellar vesicles. The steady-state fluorescence polarization of 1,6-diphenyl-1,3,5- hexatriene (DPH) has been used to detect temperature-induced structural changes in these membranes. In addition, electron microscopy has revealed vastly different fracture-face morphologies for large multilamellar vesicles “jet-frozen” from different temperatures. These data have been iriterpreted in terms of proposed phase diagrams for this lipid mixture. The shapes of the proposed phase diagrams have led us to conclude that phosphatidylcholine and sphingomyelin species of similar acyl chain length mix freely in both highly curved and uncurved bilayers, except at temperatures at which both lipids are in low-temperature, ordered phases. In addition, the similarity of these phase diagrams to phase diagrams for analogous mixtures of pure phosphatidylcholines suggested that sphingomyelin and phosphatidylcholine species might substitute for each other in supporting the lamellar phase necessary to cell membrane structure. Finally, the anisotropy of DPH fluorescence was found to be essentially invariant with sphingomyelin content at temperatures just above and below the solid-liquid phase separation in small unilamellar vesicles. This demonstrates that the sphingomyelin backbone, per se, does not order the membrane bilayer. These results are discussed in terms of the possible role of sphingomyelin in controlling acyl chain order withiri mammalian cell membranes.
UR - http://www.scopus.com/inward/record.url?scp=0019887624&partnerID=8YFLogxK
U2 - 10.1021/bi00527a010
DO - 10.1021/bi00527a010
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C2 - 7317355
AN - SCOPUS:0019887624
SN - 0006-2960
VL - 20
SP - 6803
EP - 6809
JO - Biochemistry
JF - Biochemistry
IS - 24
ER -