title: Partitioning of pyrene-labeled phospho- and sphingolipids between ordered and disordered bilayer domains.
abstract: Here we have studied how the length of the pyrene-labeled acyl chain (n) of a phosphatidylcholine, sphingomyelin, or galactosylceramide affects the partitioning of these lipids between 1), gel and fluid domains coexisting in bovine brain sphingomyelin (BB-SM) or BB-SM/spin-labeled phosphatidylcholine (PC) bilayers or 2), between liquid-disordered and liquid-ordered domains in BB-SM/spin-labeled PC/cholesterol bilayers. The partitioning behavior was deduced either from modeling of pyrene excimer/monomer ratio versus temperature plots, or from quenching of the pyrene monomer fluorescence by spin-labeled PC. New methods were developed to model excimer formation and pyrene lipid quenching in segregated bilayers. The main result is that partition to either gel or liquid-ordered domains increased significantly with increasing length of the labeled acyl chain, probably because the pyrene moiety attached to a long chain perturbs these ordered domains less. Differences in partitioning were also observed between phosphatidylcholine, sphingomyelin, and galactosylceramide, thus indicating that the lipid backbone and headgroup-specific properties are not severely masked by the pyrene moiety. We conclude that pyrene-labeled lipids could be valuable tools when monitoring domain formation in model and biological membranes as well as when assessing the role of membrane domains in lipid trafficking and sorting.
authors.affiliation: Institute of Biomedicine, Department of Biochemistry, University of Helsinki, Helsinki, Finland.
authors.forename: Mirkka
authors.initials: M
authors.lastname: Koivusalo
authors.forename: Joni
authors.initials: J
authors.lastname: Alvesalo
authors.forename: Jorma A
authors.initials: JA
authors.lastname: Virtanen
authors.forename: Pentti
authors.initials: P
authors.lastname: Somerharju
mesh_terms: D005470:Fluorometry / Q000379:methods; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D046911:Macromolecular Substances; D008560:Membrane Fluidity; D021962:Membrane Microdomains / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D044367:Phase Transition; D010743:Phospholipids / Q000737:chemistry*; D011721:Pyrenes; D013107:Sphingolipids / Q000737:chemistry*; D013194:Staining and Labeling; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D046911:Macromolecular Substances; D010743:Phospholipids; D011721:Pyrenes; D013107:Sphingolipids; C030984:pyrene