Changes in lipid and apolipoprotein composition of pig lipoproteins facilitated by rabbit lipid transfer protein.

A lipid transfer protein has been purified from the lipoprotein-free fraction of rabbit plasma. Rabbit lipid transfer protein, which was purified 600-700-fold with a 4% recovery, has an apparent Mr of 68 000 and facilitates the transfer of isotopically labelled cholesteryl ester, triacylglycerol and phosphatidylcholine between low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Rabbit lipid transfer protein, which appears to be very similar to the cholesteryl ester exchange protein previously purified from human plasma, was incubated with pig plasma at 37 degrees C for up to 6 h. Analysis of very-low-density lipoprotein (VLDL, d less than 1.006 g/ml), LDL (d 1.019-1.063 g/ml) and HDL (d 1.090-1.21 g/ml) after incubation showed that lipid transfer protein had a marked effect on the composition of the lipoprotein classes. The VLDL became enriched with cholesteryl ester and depleted of triacylglycerol. The LDL and HDL became enriched with triacylglycerol. In addition to these changes in lipid composition there were also changes in apolipoprotein composition. The most prominent change in apolipoprotein distribution was a marked increase in the apolipoprotein E content of LDL which was observed only after incubation in the presence of lipid transfer protein.