Authors: Nikita V Ivanisenko Sergei A Dzuba
Publish Date: 2013/01/22
Volume: 44, Issue: 8, Pages: 883-891
Abstract
Electron spin echo ESE spectroscopy a pulsed version of electron paramagnetic resonance EPR was applied to spinlabeled stearic acids in phospholipid bilayers hydrated in the presence of sucrose and sorbitol which are known for their cryoprotective action on biological membranes The phospholipids were 12dipalmitoylsnglycero3phosphocholine DPPC and 1palmitoyl2oleoylsnglycero3phosphocholine POPC Stearic acids were labeled by nitroxide 44dimethyloxazolidine1oxyl DOXYL attached rigidly at either the 5th or 16th specific carbon positions ESE detects fast stochastic smallangle restricted molecular rotations stochastic molecular librations with correlation times on the nanosecond timescale These motions are believed to have the same nature as the anharmonic motions of hydrogen atoms in biological substances detected by neutron scattering and Mössbauer spectroscopy which become active above 200 K To ensure that the echo decays indeed originate from fast stochastic molecular librations a threepulse stimulated spin echo was employed It was found that the presence of sucrose or sorbitol suppresses the observed molecular motions The observed effect was nearly the same for both label positions indicating that the motions are similarly suppressed near the bilayer surface and in the bilayer interior This finding suggests nonspecific interactions of sugars with bilayer surface which are likely to influence only the bulk physical properties of hydrated membranes The results obtained show the usefulness of spinecho EPR of spin labels when applied to investigate the molecular mechanisms of action of cryoprotective agents on biological systemsWe are grateful to NP Isaev for his assistance with the experiments Our work was supported by the Russian Foundation for Basic Research grant no 120300192 and the Ministry of Education and Science of the Russian Federation contract no 11519111006
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