Interchange of apolipoproteins between chylomicrons and high density lipoproteins during alimentary lipemia in man.

Apolipoproteins of the "C" group in human blood plasma, which contain the activator of the lipoprotein lipase-substrate interaction, were found to be transferred specifically from serum to phospholipid-stabilized fat emulsion. Content and distribution of apoprotein activator were measured in healthy men in the postabsorptive state and 4 h after ingestion of meals containing 100 g fat. Content of activator protein in whole serum did not change after ingestion of the fat-rich meals but that contained in triglyceride-rich lipoproteins of density (d) <1.006 approximately doubled whereas that of high density lipoproteins fell by half. The increased activator content of triglyceride-rich lipoproteins was virtually confined to chylomicrons and its concentration in chylomicron apoprotein was substantially greater than that in very low density lipoproteins. This difference could be ascribed largely to a higher content of C apoproteins in chylomicron protein since both the concentration of C apoproteins and of apoprotein activator were directly proportional to particle diameter while the pattern of fast-migrating C apoproteins in polyacrylamide gels was similar among chylomicrons and subfractions of very low density lipoproteins. Apparent concentration of activator protein was much greater in the high density lipoprotein subfraction of d 1.063-1.125 than in the subfraction of d 1.125-1.21. In the subfraction of d 1.063-1.125, the concentration of activator protein and of fast-migrating C apoproteins in polyacrylamide gels decreased after the fat-rich meal. Concentration of phospholipids in this fraction increased gradually to a peak 43% above the basal value 6 h after the meal. The results obtained demonstrate that high density lipoproteins contribute certain functionally important polar constituents to chylomicrons during alimentary lipemia in man and suggest that they also receive surface constituents from chylomicrons during the course of their metabolism.