Free Energy and Entropy of Activation for Phospholipid Flip-Flop in Planar Supported Lipid Bilayers

Abstract

Basic transition state theory is used to describe the activation thermodynamics for phospholipid flip-flop in planar-supported lipid bilayers (PSLBs) prepared by the Langmuir-Blodgett/Langmuir-Schaeffer method. The kinetics of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) flip-flop were determined as a function of temperature and lateral surface pressure using sum-frequency vibrational spectroscopy (SFVS). From the temperature and lateral pressure dependent DSPC flip-flop kinetics, a complete description of the activation thermodynamics for flip-flop in the gel state, including free energy of activation (DeltaG(++)), area of activation (Deltaa(++)), and entropy of activation (DeltaS(++)), was obtained. The free energy barrier for flip-flop of DSPC was determined to be DeltaG(++) = 105 +/- 2 kJ/mol at 40 degrees C at a deposition surface pressure of 30 mN/m. The free energy barrier was found to consist of large opposing entropic and enthalpic contributions. The influence of alkyl chain length on the activation thermodynamics of flip-flop was also investigated. Decreasing the alkyl chain length led to a decrease in DeltaG(++) due primarily to an increase in DeltaS(++). The values obtained here are compared to previous studies investigating flip-flop by vesicle based methods.

Phospholipid flip-flop modulated by transmembrane peptides WALP and melittin

“…This work expands upon our studies of the kinetics and thermodynamics of lipids in homgenous(Anglin et al, 2008) and binary lipid mixtures(Anglin and Conboy, 2008a) and a previous work, in which we demonstrated enhanced flip-flop in lipid bilayers containing the dimeric transmembrane peptide gramicidin A. (Anglin et al, 2007)…”

“…We have presented a complete description of the activation thermodynamics for DSPC flip-flop elsewhere, and details of the approach may be found in reference (Anglin et al, 2008). Briefly, by collecting both pressure and temperature dependent kinetics of lipid flip-flop, it is possible to accurately determine the complete set of thermodynamic parameters that govern the net free energy barrier (Δ G ‡ ).…”

1H NMR Shows Slow Phospholipid Flip-Flop in Gel and Fluid Bilayers

“…54,55 We therefore restrict the following discussion to supported bilayers prepared using LB/LS deposition onto uncushioned quartz substrates, for which extensive flip-flop data exist. 14,17 Below, we discuss three possible explanations for the differences in flip-flop rates in this system compared with vesicles: these include the phase state of the sample, the presence of bilayer curvature in vesicles, and the presence of topological bilayer defects such as edges and pores in SSBs.…”

“…11−13 Even less is known about flip-flop kinetics of lipids in the highly ordered gel state. 14−17 The frequent use of extrinsic probe molecules has undoubtedly contributed to the controversy surrounding spontaneous lipid translocation.…”

Lipid somersaults: Uncovering the mechanisms of protein-mediated lipid flipping

“…Techniques such as small-angle neutron scattering and sum-frequency vibrational spectroscopy that do not require lipids labeled with bulky reporter groups are promising but have yielded contradictory results in a few instances. For example, using sum-frequency vibrational spectroscopy, fast flip-flop rates (t 1/2 <10 min) were measured for DPPC and DMPC in supported fluid bilayers attached directly to silica [197–199]. In comparison, flip-flop was predictably slow in bilayers formed on polymer supports [200], suggesting that the roughness of the silica surface induces imperfections within the bilayer which promote fast flipping [201].…”