Evidence for condensed lipid/cholesterol complexes in lipid membranes

COLL 69

Maria Ratajczak, mkratajczak@gmail.com1, Shelli L Frey, sfrey@uchicago.edu2, Eva Y. Chi, evachi@fenjing.com2, Canay Ege, canayege@midway.uchicago.edu3, Jaroslaw Majewski, jarek@lanl.gov4, Kristian Kjaer, kristian.kjaer@nbi.ku.dk5, Theodore Steck, t-steck@uchicago.edu6, Yvonne Lange, Yvonne_Lange@rush.edu7, and Ka Yee C. Lee, kayeelee@uchicago.edu2. (1) Department of Physics, The Institute for Biophysical Dynamics and The James Franck Institute, The University of Chicago, Chicago, IL 60637, (2) Department of Chemistry, The Institute for Biophysical Dynamics and The James Franck Institute, The University of Chicago, 929 E. 57th St., CIS-ESB31, Chicago, IL 60637, (3) Department of Chemistry, The Insitute for Biophysical Dynamics and The James Franck Institute, The University of Chicago, CIS-ESB31, 929 E. 57th Street, Chicago, IL 60637, (4) LANSCE-12, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87544, (5) Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark, (6) Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, (7) Department of Pathology, Rush University Medical Center, Chicago, IL 60612
Certain binary mixtures of phospholipids and cholesterol exhibit phase diagrams with two immiscibility regions with a sharp cusp in between. The cusp has been suggested to represent the stoichiometry of phospholipid/cholesterol complexes, and cholesterol is thought to exist in two states: a bound, low activity state, and an unbound, high activity state. To better understand the interaction between phospholipids and cholesterol, we have studied the effect of a possible displacing agent, hexadecanol, on the behavior of the binary mixture. Our cholesterol desorption assays indicate that hexadenanol can displace cholesterol from its association with phospholipids, thereby activating it. Phospholipid/cholesterol/hexadecanol systems in which a fraction of cholesterol is replaced by the alcohol have phase diagrams that mimic those of binary systems with the same apparent molar stoichiometry. X-ray data show a broad Bragg peak in these binary systems, indicating that order in these complexes extend over only several molecular dimensions.
 

Biological Surface Chemistry
8:30 AM-11:50 AM, Monday, March 26, 2007 McCormick Place South -- Room S404A, Level 4, Oral

Division of Colloid & Surface Chemistry

The 233rd ACS National Meeting, Chicago, IL, March 25-29, 2007