Sterol Carrier and Lipid Transfer Proteins

Abstract

Publisher Summary The discovery of the lipid exchange, transfer, or carrier proteins is a result of the findings that cells contained cytosolic factors that were required for microsomal synthesis of cholesterol or could accelerate the transfer or exchange of phospholipids between membrane preparations. Most of the lipid exchange transfer or carrier activities have been characterized as cytosolic factors. These activities might be concentrated in cell particulate fractions, such as microsomes, and might be released to varying extents by tissue homogenization and/or treatment of the “cytosolic” fraction. The phospholipid exchange and transfer activities have been determined by the exchange or transfer of labeled phospholipids between microsomes and mitochondria or liposomes. These more direct assays involving aspects of cholesterol metabolism suggest the possibility that there is greater biological specificity for sterol carrier protein 2 (SCP 2) than is implied by the term non-specific lipid transfer protein. Another protein with apparent biological specificity is fatty acid-binding protein (FABP). Three approaches have been employed to determine fatty acid-binding protein (FABP) activities: Sephadex G-50 chromatography of liver cytosol following addition of [14 C] oleate; use of hydrophobic Lipidex 1000 to separate FABP-bound from unbound fatty acids; and immunoprecipitation technique.