Cholesterol ester exchange between human plasma high and low density lipoproteins mediated by a plasma protein factor

Although unesterified cholesterol and phospholipids exchange freely, a protein factor from the d greater than 1.25 g/ml plasma fraction was found to be necessary for cholesterol esters to transfer from HDL to LDL. This transfer was reversible, time-dependent and a function of the concentration of the d greater than 1.25 fraction, but independent of lecithin : cholesterol acyltransferase reaction. The transfer represented an equilibration of molecules, but no net mass transfer of cholesterol esters could be demonstrated from HDL to LDL.