Some characteristics of a high molecular weight lipid-protein aggregate and its possible role in intracellular fatty acid metabolism.

Several physical aspects of a high molecular weight lipid-protein aggregate separated by gel chromatography from chick and rat liver cytosol and its possible role in intracellular fatty acid metabolism were investigated. Electron microscopic examination of the high molecular weight lipid-protein aggregate indicated spherical particles with a diameter range of 200-600 A. This structure is consistent with a microemulsion particle of triglyceride encapsulated by phospholipid and protein. Uptake of fatty acids by microsomes occurred from the same lipid-protein aggregate, and the triglycerides synthesized in microsomes also became associated with these particles in the cytosol. The lipid-protein aggregate prepared by different homogenization methods showed identical ratios of components, but these ratios changed following incubation. These findings lend support to the concept that this aggregate plays a physiological role in intracellular lipid metabolism, and may be identifiable with previously reported subcellular fatty acid and triglyceride pools.