Phosphatidyl choline interaction with bovine serum albumin: effect of the physical state of the lipid on protein-lipid complex formation.

Radioactively labeled [¹⁴C]phosphatidyl choline dispersed on Celite was equilibrated with bovine serum albumin solutions buffered at pH 8.0. Phosphatidyl choline was rapidly solubilized in the presence of serum albumin, and formed stable protein-lipid complexes which were isolated by gel-filtration through a Sepharose 4B column. Under similar conditions, equilibration of the protein with phosphatidyl choline liposome dispersions in buffer did not result in complex formation. The altered physical state of phosphatidyl choline on the weakly adsorbing Celite surface appears to be essential for binding by native bovine serum albumin. This work reports the first observation of phosphatidyl choline binding to native serum albumin in bulk phase and suggests the possibility of exposing monodisperse lipids, under controlled conditions, to proteins having lipid binding properties.