title: A calorimetric study of binary mixtures of dihydrosphingomyelin and sterols, sphingomyelin, or phosphatidylcholine.
abstract: The thermotropic properties of binary mixtures of D-erythro-n-palmitoyl-dihydrosphingomyelin (16:0-DHSM), D-erythro-n-palmitoyl-sphingomyelin (16:0-SM), cholesterol, lathosterol, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) were studied by differential scanning calorimetry. Addition of sterol to 16:0-DHSM and 16:0-SM bilayers resulted in a progressive decrease in both the T(m) and the enthalpy of the main transition. The sterol-induced broad components in 16:0-DHSM endotherms had markedly lower enthalpies than those induced in 16:0-SM. Pretransitions recorded in 16:0-DHSM and 16:0-SM membranes responded differently to low concentrations of cholesterol. The presence of 5 mol % cholesterol increased the pretransition temperature in 16:0-SM bilayers, whereas it decreased the temperature in 16:0-DHSM membranes. Lathosterol behaved in general as cholesterol with regard to its effects on the thermotropic behavior of both sphingolipids, but it appeared to form more stable sterol-rich domains, as seen from the higher T(m) of the broad component, in comparison to cholesterol. Thermograms recorded on binary mixtures of 16:0-SM:16:0-DHSM and DPPC:16:0-DHSM showed that 16:0-SM mixed nearly ideally with 16:0-DHSM, whereas DPPC mixing was less ideal in a 16:0-DHSM membrane. In conclusion, we observed that 16:0-DHSM interactions with sterols differed from that seen with 16:0-SM, and that 16:0-DHSM mixed better with 16:0-SM than DPPC, which indicates that DHSM could function as a membrane organizer within laterally condensed domains.
authors.affiliation: Department of Biochemistry and Pharmacy, Abo Akademi University, PO Box 66, FIN 20521 Turku, Finland. thomas.nyholm@abo.fi
authors.forename: Thomas K M
authors.initials: TK
authors.lastname: Nyholm
authors.forename: Matts
authors.initials: M
authors.lastname: Nylund
authors.forename: J Peter
authors.initials: JP
authors.lastname: Slotte
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D002152:Calorimetry, Differential Scanning / Q000379:methods*; D002784:Cholesterol / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008968:Molecular Conformation; D010713:Phosphatidylcholines / Q000737:chemistry*; D012996:Solutions; D013109:Sphingomyelins / Q000737:chemistry*; D013261:Sterols / Q000737:chemistry*; D013696:Temperature
chemical_list: C091181:4,5-dihydrosphingomyelin; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D012996:Solutions; D013109:Sphingomyelins; D013261:Sterols; D015060:1,2-Dipalmitoylphosphatidylcholine; C001521:lathosterol; D002784:Cholesterol