This chapter describes the use of a nonspecific lipid transfer protein to vary the cholesterol-to-phospholipid (Ch/PL) ratio of membranes. The method is illustrated with synaptosomes and synaptic plasma membranes, where loss of sodium-dependent γ-aminobutyric acid uptake is correlated with decreased Ch/PL ratio in the membrane. The method consists of incubating the membranes with the transfer protein in the presence of lipid vesicles containing either cholesterol and phosphatidylcholine (PC) or PC alone, resulting in net transfer of cholesterol to the membranes or net removal of cholesterol from the membranes, respectively. The nonspecific lipid transfer protein is purified from beef liver. The transfer protein is prepared without the heat treatment and octylagarose column chromatography steps. This shortened procedure increases the yield of transfer activity. Assay of nonspecific lipid transfer activity is based on measurement of transfer of radiolabeled cholesterol to heat-treated beef heart mitochondria. A trace of radiolabeled triolein is included in the liposomes as a nontransferable marker. © 1983, Elsevier Inc. All rights reserved.
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