European Biophysics Journal

, Volume 41, Issue 2, pp 147–159 | Cite as

Phases and domains in sphingomyelin–cholesterol membranes: structure and properties using EPR spin-labeling methods

  • Laxman Mainali
  • Marija Raguz
  • Witold K. Subczynski
Original Paper


EPR spin-labeling methods were used to investigate the order and fluidity of alkyl chains, the hydrophobicity of the membrane interior, and the order and motion of cholesterol molecules in coexisting phases and domains, or in a single phase of fluid-phase cholesterol/egg-sphingomyelin (Chol/ESM) membranes with a Chol/ESM mixing ratio from 0 to 3. A complete set of profiles for these properties was obtained for the liquid-disordered (ld) phase without cholesterol, for the liquid-ordered (lo) phase for the entire region of cholesterol solubility in this phase (from 33 to 66 mol%), and for the lo-phase domain that coexists with the cholesterol bilayer domain (CBD). Alkyl chains in the lo phase are more ordered than in the ld pure ESM membrane. However, fluidity in the membrane center is greater. Also, the profile of hydrophobicity changed from a bell to a rectangular shape. These differences are enhanced when the cholesterol content of the lo phase is increased from 33 to 66 mol%, with clear brake-points between the C9 and C10 positions (approximately where the steroid-ring structure of cholesterol reaches into the membrane). The organization and motion of cholesterol molecules in the CBD are similar to those in the lo-phase domain that coexists with the CBD.


Membrane domain Cholesterol Liquid-ordered phase Spin-labeling EPR Sphingomyelin 


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Copyright information

© European Biophysical Societies' Association 2011

Authors and Affiliations

  • Laxman Mainali
    • 1
  • Marija Raguz
    • 1
    • 2
  • Witold K. Subczynski
    • 1
  1. 1.Department of BiophysicsMedical College of WisconsinMilwaukeeUSA
  2. 2.Department of Medical Physics and Biophysics, School of MedicineUniversity of SplitSplitCroatia

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