Monovalent cation-induced fusion of acidic phospholipid vesicles

✍ Scribed by Kari K. Eklund

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 591 KB
• Volume: 52
• Category: Article
• ISSN: 0009-3084
• DOI: 10.1016/0009-3084(90)90115-8

✦ Synopsis

Fusion of small unilamellar vesicles (SUV) consisting of dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG) and phosphatidylglycerol (PG) from egg yolk, dipalmitoylphosphatidylserine (DPPS) and phosphatidylserine (PS) from bovine brain was studied as a function of monovalent cation concentration. Fusion was detected by measuring the changes in the excimer to monomer fluorescence intensity ratio (/E/U) of pyrene-labeled phospholipid analogues upon fusion of the pyrenelabeled and unlabeled vesicles. No fusion was observed for vesicles consisting of DMPC, PS from bovine brain or PG from egg yolk upon addition of NaC1 (up to 1 M). However, considerable fusion was evident for vesicles consisting of DMPG or DPPS upon addition of monovalent cations (300 mM to 1 M). Fusion kinetics were fast reaching a plateau after 5 min of addition of cations. The order of efficiency of different monovalent cations to induce the fusion of DMPG vesicles as judged by the changes of the IE/M ratio was Li+> Na+> K+> Cs ÷. DSC-scan of sonicated DMPG vesicles showed, in the absence of salt, a phase transition at 19.2°C with enthalpy of 1.1 kcal • mo1-1. After incubation in the presence of 600 mM NaC1 the DSC scan showed a narrow phase transition at 24.1°C with enthalpy of 6.9 kcal. mole -1 and a pronounced pretransition, both supporting that the fusion of the vesicles had occurred in the presence of NaCI. The results indicate that sonicated vesicles consisting of acidic phospholipids with fully saturated fatty acids fuse in the presence of monovalent cations, whereas those containing unsaturated fatty acids do not.