A structural transition in egg lecithin-cholesterol bilayers at 12 °C |
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Authors: | R.P. Rand W.A. Pangborn |
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Affiliation: | Department of Biological Sciences, Brock University, St. Catharines Canada |
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Abstract: | The thermal coefficient of expansion of egg lecithin bilayer thickness, αd1, was measured as a function of its cholesterol content up to mole ratio lecithin/cholesterol of 1:1, and over the temperature range 0–40 °C. At all cholesterol contents αd1 changes abruptly at approximately 12 °C indicating a structural transition at this temperature. Above 12 °C, αd1 decreases monotonically from −2·10−3 for pure egg lecithin to −1·10–3 at mole ratio 1:1. Below 12 °C αd1 is walways higher than above 12 °C and shows a sharp, anomalously high value of −6·10−3 at the mole ratio 2:1. The results have been interpreted as the movement of cholesterol into the bilayer or the formation of lecithin-cholesterol “complexes” at temperatures below 12 °C. Similar studies with phosphatidylinositol containing cholesterol showed no structural transition and lysolecithin containing cholesterol behaved differently giving two lamellar phases in equilibrium. |
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