Studies on the molecular packing of mixed dispersions of Triton X-100 and sphingomyelin and its dependence on temperature and cloud point

Cholesterol reverts Triton X‐100 preferential solubilization of sphingomyelin over phosphatidylcholine: A 31P‐NMR study

“…Previous reports have suggested that SM is solubilized by Triton X-100 more readily than PC [9,10,27], and that SM-Chol mixtures are particularly resistant to Triton X-100 solubilization [10,15,28,29]. However, most of these observations can be criticized [4] on the basis of two considerations, namely that: (i) no quantification of the individual lipid classes in the range of co-existence was carried out and/or (ii) quantification of the lipids solubilized under certain conditions was performed after physical separation of the mixed micellar and bilayer fractions, e.g.…”

“…Based on the available data regarding solubilization of different individual phospholipids and on the physical properties of bilayers made of lipid mixtures [9,15,16], we suggest that the resistance of SM towards solubilization is due to its interaction with cholesterol. The arguments in favour of a preferred association of sterols to SM over PC of natural origin have been reviewed recently [17].…”

“…2) [8,25], than for those formed of pure SM (ca. 0.5) [9,10], at room temperature. In the presence of Chol, R sol t was much higher (>4).…”

“…multilamellar liposomes (MLV), the NMR line shape associated with the phosphoryl group is inhomogeneously broadened, because the magnetic dipolar interactions are not fully averaged spatially [19,20]. Nonetheless the much smaller lipid-detergent mixed micelles (Stokes radius 30-40 Å) tumble at a rate sufficiently fast to equalize magnetically all the molecules, thus cancelling the heterogeneity, and yielding narrow NMR signals [9,21,22]. Under appropriate conditions, signals arising from SM and PC in mixed micelles can be resolved.…”

Principles of microdomain formation in biological membranes— Are there lipid liquid ordered domains in living cellular membranes?

“…Another possibility is that`resistant bilayers' are those made of sphingomyelin or other sphingolipids. This can be discarded since solubilization of bilayers made of egg SM requires less TR than solubilization of egg PC (52,54,55). Furthermore, other sphingolipids supposed to exist in rafts, such as gangliosides, actually facilitate bilayer solubilization by TR (53).…”