Sterol release in mammalian cells. The role of a liposomal-free albumin-phospholipid complex.

Human serum albumin, the purity of which was confirmed by two-dimensional gel electrophoresis and high-pressure liquid chromatography, is able to bind dipalmitoyl phosphatidylcholine and the resulting albumin-phospholipid complex can cause marked sterol release from animal and human cells in tissue culture. The complex-induced sterol release was synergistic, exceeding by 4--5-fold the sum of sterol release in the presence of albumin and phospholipid individually. Isolation of the albumin-phospholipid complex by gel permeation chromatography yielded a liposomal-free fraction which caused full sterol release. No synergistic release of sterol occurred when cells were incubated with human serum albumin and dilinoleoyl phosphatidylcholine.