title: Lipid flip-flop in binary membranes composed of phosphatidylserine and phosphatidylcholine.
abstract: The kinetics and thermodynamics of lipid flip-flop in bilayers composed of 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) were studied using sum-frequency vibrational spectroscopy. The kinetics of DSPC and DPPS flip-flop were examined as a function of temperature and bilayer composition. The rate of DSPC flip-flop did not exhibit any significant dependence on bilayer composition while the rate of DPPS flip-flop was inversely dependent on the mole fraction of DPPS. The transition-state thermodynamics for DSPC and DPPS lipids in these mixed bilayers were determined in order to identify the energetic impact of the phosphatidylserine headgroup on lipid flip-flop. The thermodynamics for the DSPC component remained statistically identical to bilayers composed entirely of DSPC. The activation energy for the DPPS component showed a linear correlation with the mole fraction of DPPS for all bilayer compositions. The enthalpy and entropy for DPPS flip-flop did not increase linearly with the fraction of DPPS but did directly correlate with the molecular area. The DPPS component also exhibited enthalpy-entropy compensation which suggests that lipid hydration may play a significant role in membrane dynamics.
authors.affiliation: Department of Chemistry, University of Utah , 315 South 1400 East, Salt Lake City, Utah 84112, United States.
authors.forename: Krystal L
authors.initials: KL
authors.lastname: Brown
authors.forename: John C
authors.initials: JC
authors.lastname: Conboy
mesh_terms: D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D010718:Phosphatidylserines / Q000737:chemistry*; D013057:Spectrum Analysis; D013816:Thermodynamics; D014732:Vibration
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; C038694:dipalmitoylphosphatidylserine; C010942:1,2-distearoyllecithin