Micellar formation of spin-labeled fatty acyl derivatives of lipophilic muramyl dipeptides and their incorporation into liposomal membranes.
A lipophilic muramyl dipeptide (MDP) with a nitroxide moiety in its acyl chain (SL-MDP) and its N-methyl derivative (SL-methyl MDP) were synthesized. The SL-MDPs formed micelles (cmc, 0.1-0.3 mM). The ESR spectra of the SL-MDPs in phosphatidylcholine (PC) liposomes at 25 degrees C consisted of an anisotropic signal and three sharp lines, indicating that both SL-MDPs partitioned between membranes and aqueous phase. The amounts of the SL-MDPs in membranes depended on the phospholipid species and the cholesterol (Chol) content, but no appreciable difference was observed between SL-MDPs. The SL-MDPs partitioned well at 25 degrees C into egg yolk PC liposomes but not into pure dipalmitoylphosphatidylcholine (DPPC), suggesting that the incorporation may be related to the membrane fluidity. Chol enhanced the incorporation into both phospholipids. The mobilities of the SL-MDPs in the membranes were less than that of the corresponding spin-labeled fatty acid. Comparison of the mobilities among SL-MDPs, spin-labeled ganglioside and spin-labeled galactosylceramide showed that the hydrophilicity of the polar group may influence the immobilization of their acyl chains.
D000119:Acetylmuramyl-Alanyl-Isoglutamine / Q000031:analogs & derivatives*; D002784:Cholesterol; D004578:Electron Spin Resonance Spectroscopy; D008081:Liposomes; D008823:Micelles; D008954:Models, Biological; D010713:Phosphatidylcholines; D013113:Spin Labels / Q000138:chemical synthesis*
D008081:Liposomes; D008823:Micelles; D010713:Phosphatidylcholines; D013113:Spin Labels; D000119:Acetylmuramyl-Alanyl-Isoglutamine; D002784:Cholesterol