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

We measured the transbilayer diffusion of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in large unilamellar vesicles, in both the gel (L β') and fluid (L α) phases. The choline resonance of headgroup-protiated DPPC exchanged into the outer leaflet of headgroup-deuterated DPPC-d13 vesicles was monitored using 1H NMR spectroscopy, coupled with the addition of a paramagnetic shift reagent. This allowed us to distinguish between the inner and outer bilayer leaflet of DPPC, to determine the flip-flop rate as a function of temperature. Flip-flop of fluid-phase DPPC exhibited Arrhenius kinetics, from which we determined an activation energy of 122 kJ mol –1. In gel-phase DPPC vesicles, flip-flop was not observed over the course of 250 h. Here, our findings are in contrast to previous studies of solid-supported bilayers, where the reported DPPC translocation rates are at least several orders of magnitude faster than those in vesicles at corresponding temperatures. Finally, we reconcile these differences by proposing a defect-mediated acceleration of lipid translocation in supported bilayers, where long-lived, submicron-sized holes resulting from incomplete surface coverage are the sites of rapid transbilayer movement.
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [1] ;  [4] ;  [5] ; ORCiD logo [1]
  1. Univ. of Graz (Austria). Inst. of Molecular Biosciences, Biophysics Division; BioTechMed-Graz (Austria)
  2. Univ. of Tennessee, Knoxville, TN (United States). Bredesen Center, Dept. of Physics and Astronomy; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Joint Inst. for Biological Sciences, Biology and Soft Matter Division
  3. Univ. of South Florida, Tampa, FL (United States). Dept. of Physics
  4. Stony Brook Univ., NY (United States). Dept. of Biochemistry and Cell Biology
  5. Univ. of Tennessee, Knoxville, TN (United States). Bredesen Center, Dept. of Physics and Astronomy; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biology and Soft Matter Division; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Shull Wollan Center-A Joint Inst. for Neutron Sciences; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy
Publication Date:
Grant/Contract Number:
AC05-00OR22725; 7394
Type:
Published Article
Journal Name:
Langmuir
Additional Journal Information:
Journal Volume: 33; Journal Issue: 15; Journal ID: ISSN 0743-7463
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
Sponsoring Org:
Austrian Science Fund (FWF); National Science Foundation (NSF); USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES
OSTI Identifier:
1342412
Alternate Identifier(s):
OSTI ID: 1352553; OSTI ID: 1362240