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Biophys J, February 2000, p. 866-873, Vol. 78, No. 2

Cholesterol Crystalline Polymorphism and the Solubility of Cholesterol in Phosphatidylserine

Richard M. Epand,* Diana Bach,dagger Nina Borochov,Dagger and Ellen Wachtel§

 *Department of Biochemistry, McMaster University, Hamilton, Ontario L8N 3Z5, Canada;  dagger Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel;  Dagger Center for Technological Education, Holon, Israel; and  §Chemical Services Unit, Weizmann Institute of Science, Rehovot, Israel

There is a marked hysteresis between the heating and cooling polymorphic phase transition of anhydrous cholesterol. At a scan rate of 0.05°C/min the difference in transition temperatures between heating and cooling scans is ~10°C. This phenomenon also occurs with mixtures of cholesterol with phosphatidylserine and can result in an underestimation of the amount of crystalline cholesterol in a sample that has not been cooled sufficiently. With 1-palmitoyl-2-oleoyl phosphatidylserine and 1-stearoyl-2-oleoyl phosphatidylserine the cholesterol crystallites form while the lipid remains in the Lalpha phase. Sonication of dimyristoyl phosphatidylserine with a 0.4 mol fraction cholesterol results in the loss of cholesterol crystallite diffraction, but only a partial loss of the polymorphic transition detected by calorimetry. We therefore conclude that the thermal history of the sample can have profound effects on the appearance of the polymorphic phase transition of cholesterol by differential scanning calorimetry. Depending on the morphology of the vesicles, diffraction methods may underevaluate the amount of cholesterol crystallites present.

Biophys J, February 2000, p. 866-873, Vol. 78, No. 2
© 2000 by the Biophysical Society   0006-3495/00/02/866/08  $2.00


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