Apoproteins in association with intralipid incubations in rat and human plasma

Intralipid was incubated with rat and human plasma and examined for changes in lipid and apoprotein composition. Upon incubation in rat plasma, Intralipid acquired an apoprotein complement similar to that found in chylomicrons following plasma incubation or in chylomicrons after alimentary lipemia. Since the apoproteins of lipoproteins probably govern their metabolism, these results suggest that Intralipid and chylomicrons undergo similar metabolic fates. This pattern is characterized by a predominance of Apo E (the arginine-rich apoprotein) and Apo C. Incubation of Intralipid with human plasma showed the uptake of Apo A-I and Apo A-IV as well. Density fractionation of the plasma into separate lipoprotein classes facilitated identification of high density lipoprotein as the major apoprotein donor to the Intralipid. When rat lipoprotein-free plasma (δ>1.21) was incubated with Intralipid, a different apoprotein pattern appeared in the particles of S_f>400 depending on whether the entire Intralipid preparation or only the S_f>400 fraction alone was incubated. The difference consisted of a virtual total absence of the arginine-rich protein on the S_f>400 particles in whole Intralipid incubations. Density fractionation of the S_f<400 particles of Intralipid and recombination of these fractions with the S_f>400 fraction before incubation revealed the major inhibitory fraction to be δ<1.006 (S_f 20–400).