Effect of temperature and plasma on the exchange of apolipoproteins and phospholipids between rat plasma very low and high density lipoproteins.

The effect of temperature and plasma on the exchange of apoprotein C and phospholipids between VLDL and HDL was studied using 125I-labeled and 32P-labeled VLDL. Temperature affected the exchange of apoproteins and phospholipids similarly, and both were enhanced by increasing the temperature of incubation to 20 degrees C and higher. The exchange of apoC was almost complete within 5 minutes of incubation and was not influenced by the addition of plasma to the incubation mixture. The exchange of phospholipids occurred much more slowly and was enhanced 5- to 10-fold in the presence of plasma. These results indicate that the exchange of both phospholipids and apoC is dependent on the temperature of the incubation, but that they exchange independently, at least in part. It is suggested that the exchange of apoC occurs through dissociation of the apoprotein from the lipoprotein surface to the water phase, whereas the exchange of phospholipids is mediated mainly by a carrier molecule present in plasma and absent in lipoproteins.