Flip-Flop of Phospholipids in Vesicles: Kinetic Analysis with Time-Resolved Small-Angle Neutron Scattering

Abstract

We applied a time-resolved small-angle neutron scattering technique to vesicle systems to determine interparticle transfer and flip-flop of phospholipids. Measurements were performed for large unilamellar vesicles, consisting of dimyristoylphosphatidylcholine (DMPC), 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), or 1-palmitoyl-2-oleoylphosphatidic acid (POPA), which differ either in their acyl chains or headgroup. POPC, which is analogous to naturally occurring phosphatidylcholines, exhibited no transbilayer transfer and very slow interbilayer migration. POPC on the inner leaflet of vesicles did not flop even when phospholipase D converted all POPC molecules on the outer leaflet into POPA, which was shown to exhibit fast flip-flop. From these results, together with the observation that the flip-flop of DMPC was entirely inhibited in the presence of cholesterol, it is deduced that the flip-flop of phosphatidylcholines does not take place spontaneously in cellular plasma membranes rich in cholesterol and that it requires enzymatic activities of energy-dependent and/or -independent flippases/floppases.

pH-dependent promotion of phospholipid flip-flop by the KcsA potassium channel

“…Cholesterol has been reported to reduce the flip-flop rate of phospholipids [25,27]. The presence of cholesterol increases the acyl chain packing order and thereby inhibits solute permeation [28].…”

Mechanism for Remodeling of the Acyl Chain Composition of Cardiolipin Catalyzed by Saccharomyces cerevisiae Tafazzin

“…Preparation of Liposomes-Liposomes (large unilamellar vesicles) made of an acyl donor and acceptor mixture (PC/MLCL, PC/dilyso-CL (DLCL), or LPC/DLCL at a 9:1 molar ratio) were prepared by the extrusion method (46,47). Stock solutions of an acyl donor and acceptor in a methanol/chloroform (1:3, v/v) solution were mixed in the required proportion.…”

“…9A, taking PC(18:1-18:1)/sn-2Ј-MLCL(18:1-18:1/18:1-OH) liposomes (9:1 molar ratio) as an example. The concentrations of PCs in liposomal preparations were determined using an enzyme assay kit for choline (Wako, Osaka, Japan) (47).…”

Exposure of phosphatidylserine on the cell surface

“…79 Once established, it takes days to disrupt the asymmetrical distribution of phospholipids because spontaneous translocation across the bilayer is extremely low. 80,81 In this regard, a scramblase(s) is essential for quick PtdSer exposure during apoptosis. Figure 4 Structure of Xkr8, and its caspase-cleavage site.…”