Biophysics Department, Faculty of Science, Cairo University, Giza, Egypt

Abstract: The mechanism of cholesterol exchange has been investigated by following the transfer of radiolabeled cholesterol from negatively charged, unilamellar donor vesicles to neutral acceptor vesicles. Donor and acceptor vesicles were incubated together and were stable to fusion over the course of the experiment. At intervals, donor and acceptor vesicles were separated by passage through a column of DEAE-Sepharose. Ion exchange chromatography was used for rapid separation of donor and acceptor (present in 10-fold molar excess) vesicles. The kinetics of [14C] cholesterol transfer between unilamellar vesicles was described and analyzed in the presence of sucrose buffer; 10% FCS (fetal calf serum) and 50% FCS. The process is first order kinetics. This means that acceleration of the off-rate must be due to donor-acceptor interactions at short distances. It was found that the presence of serum in the medium greatly diminished rather than increased the total transfer of radiolabelled cholesterol from donor vesicles to the acceptor vesicles.

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