Membrane Fluidity and Lipid Composition
The fluidity of a fluid is the reciprocal of its viscosity which in turn is a measure of the resistance of the fluid to movement within it 1, 2. The unit of viscosity is the Poise (P) and, measured by the motion of various physical probes, membranes at ambient temperatures seem to be far more viscous or far less fluid than ordinary liquids which are of the order of 10−2 poise or a centipoise (cP). The viscosity of red blood cell membranes was found to vary from 2.0 to 6.0 P with increasing cholesterol/phospholipid ratios 3. Fluid lecithin phospholipid membranes have viscosities around 1 P at temperatures of 30° 4, which is approximately the viscosity of light oil 5.
KeywordsCholesterol Enthalpy Serine Choline Deuterium
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