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Laxman Mainali, Marija Raguz, William O'Brien, Witold Subczynski; Domain Structure of Reconstituted Cortical and Nuclear Human Lens Lipid Membranes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5746.
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© ARVO (1962-2015); The Authors (2016-present)
To study the organization and properties of human lens lipid membranes made from total lipids extracted from the cortical and nuclear regions of the human eye lenses. This research is important for studying intact human lens membranes and for elucidating the effect of membrane proteins on the lateral organization of the lipid bilayer portion of the membranes.
Using electron paramagnetic resonance (EPR) spectroscopy and lipid spin labels, membrane properties including profiles of the phospholipid alkyl-chain order, fluidity, oxygen transport parameter, and hydrophobicity were investigated. This method provided a unique opportunity to discriminate between coexisting lipid domains.
Cortical and nuclear lens lipid membranes contain two distinct lipid environments: the bulk phospholipid-cholesterol domain and the cholesterol bilayer domain (CBD). The alkyl chains of phospholipids were strongly ordered at all depths. However, profiles of the membrane fluidity, which depend on the rotational motion of spin labels and explicitly contain time (expressed as the spin-lattice relaxation rate), showed relatively high fluidity of alkyl chains close to the membrane center. Profiles of the oxygen transport parameter and hydrophobicity were a rectangular shape with an abrupt change between the C9 and C10 positions, which is approximately where the steroid ring structure of cholesterol reaches into the membrane. The amount of CBD was greater in nuclear membranes than in cortical membranes.
The crucial role in determining fiber cell membrane properties is played by an extremely high, saturating cholesterol content. EPR techniques are useful in studying membrane domains.
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