Medical College of Wisconsin
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Characterization of lipid domains in reconstituted porcine lens membranes using EPR spin-labeling approaches. Biochim Biophys Acta 2008 Apr;1778(4):1079-90



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The physical properties of membranes derived from the total lipid extract of porcine lenses before and after the addition of cholesterol were investigated using EPR spin-labeling methods. Conventional EPR spectra and saturation-recovery curves indicate that the spin labels detect a single homogenous environment in membranes before the addition of cholesterol. After the addition of cholesterol (when cholesterol-to-phospholipid mole to mole ratio of 1.55-1.80 was achieved), two domains were detected by the discrimination by oxygen transport method using a cholesterol analogue spin label. The domains were assigned to a bulk phospholipid-cholesterol bilayer made of the total lipid mixture and to a cholesterol crystalline domain. Because the phospholipid analogue spin labels cannot partition into the pure cholesterol crystalline domain, they monitor properties of the phospholipid-cholesterol domain outside the pure cholesterol crystalline domain. Profiles of the order parameter, hydrophobicity, and oxygen transport parameter are identical within experimental error in this domain when measured in the absence and presence of a cholesterol crystalline domain. This indicates that both domains, the phospholipid-cholesterol bilayer and the pure cholesterol crystalline domain, can be treated as independent, weakly interacting membrane regions. The upper limit of the oxygen permeability coefficient across the cholesterol crystalline domain at 35 degrees C had a calculated value of 42.5 cm/s, indicating that the cholesterol crystalline domain can significantly reduce oxygen transport to the lens center. This work was undertaken to better elucidate the major factors that determine membrane resistance to oxygen transport across the lens lipid membrane, with special attention paid to the cholesterol crystalline domain.

Author List

Raguz M, Widomska J, Dillon J, Gaillard ER, Subczynski WK


Witold K. Subczynski PhD Professor in the Biophysics department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Biological Transport
Electron Spin Resonance Spectroscopy
Hydrophobic and Hydrophilic Interactions
Lens, Crystalline
Membrane Microdomains
Spin Labels
Sus scrofa