Open Access1H NMR Shows Slow Phospholipid Flip-Flop in Gel and Fluid Bilayers
Author(s) -
Drew Marquardt,
Frederick A. Heberle,
Tatiana Miti,
Barbara Eicher,
Erwin London,
John Katsaras,
Georg Pabst
Publication year - 2017
Publication title -
langmuir
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.042
H-Index - 333
eISSN - 1520-5827
pISSN - 0743-7463
DOI - 10.1021/acs.langmuir.6b04485
Subject(s) - vesicle , chemistry , bilayer , phospholipid , arrhenius equation , lipid bilayer , deuterium nmr , kinetics , phase (matter) , crystallography , analytical chemistry (journal) , activation energy , arrhenius plot , diffusion , nuclear magnetic resonance spectroscopy , membrane , stereochemistry , chromatography , thermodynamics , organic chemistry , physics , quantum mechanics , biochemistry
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 1 H 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. 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. 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.