A Calorimetric Study of the Thermotropic Behavior of Aqueous Dispersions of Natural and Synthetic Sphingomyelins

Y. Barenholz, J. Suurkuusk, D. Mountcastle, T. E. Thompson, R. L. Biltonen

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Abstract

A recently developed differential scanning calorimeter has been used to characterize the thermotropic behavior of aqueous dispersions of liposomes containing sphingomyelin. Liposomes derived from sheep brain sphingomyelin exhibit a broad gel-liquid crystalline phase transition in the temperature range of 20-45 °C. The transition is characterized by maxima in the heat capacity function at 31.2 and 37.1 °C and a total enthalpy change of 7.2 ± 0.4 kcal/mol. Beef brain sphingomyelin liposomes behave similarly but exhibit heat capacity maxima at 30, 32, and 38 °C and a total enthalpy change of 6.9 kcal/mol. The thermotropic behavior of four pure synthetic sphingomyelins is reminiscent of multilamellar lecithin liposomes in that a single, sharp, main transition is observed. Results obtained for liposomes containing mixtures of different sphingomyelins are complex. A colyophilized mixture of N-palmitoylsphingosinephosphorylcholine, N-stearoylsphingosinephosphorylcholine, and N-lignocerylsphingosinephosphorylcholine in a 1:1:1 mol ratio exhibits a single transition with a Tm below that observed for the individual components. On the other hand a 1:1 mixture of N-stearoylsphingosinephosphorylcholine and 1-palmitoyl-2-oleylphosphatidylcholine exhibits three maxima in the heat capacity function. It is clear from these results that the thermotropic behavior of sphingomyelin-containing liposomes is a complex function of the exact composition. Furthermore, it appears that the behavior of the liposomes derived from natural sphingomyelins cannot be explained in terms of phase separation of theindividual components.

Original languageEnglish
Pages (from-to)2441-2447
Number of pages7
JournalBiochemistry
Volume15
Issue number11
DOIs
StatePublished - 1 Jun 1976
Externally publishedYes

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