Stability of Phospholipid Binding in Human Serum Lipoproteins

¹ From the Radioisotope Service, Veterans Administration Hospital, Long Beach, and the Department of Physiological Chemistry, School of Medicine, University of California, Los Angeles, California

The specific activity of lipid phosphorus in both - and ß-lipoproteins obtained from labeled human serum by electrophoresis and ultracentrifugation was the same within experimental error. This remained true for 8 days after tracer administration. From this it is concluded that the exchange of phospholipids between lipoprotein ‘molecules’ must be rapid compared to the metabolic half-life of the phospholipid molecules. Such an exchange was demonstrated to occur even in vitro. These data support the view that lipoproteins may consist of protein and mixed lipid micelles held in loose ionic association.