Influence of divalent cations on rat apolipoprotein transfer to synthetic lipoproteinlike lipid emulsions in vitro

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Abstract
Synthetic lipid emulsions of chylomicron (TG1) and low density lipoprotein (TG2) diameter, consisting of triacylglycerol and phosphatidylcholine, were incubated with rat serum, whole blood, plasma, and postheparin plasma in the presence or absence of divalent cations. The lipid and apoprotein composition of the reisolated Sf > 400 particles was examined by high temperature gas chromatography and sodium dodecyl sulfate – glycerol polyacrylamide gel electrophoresis, respectively. It was found that apoproteins C, E, H, and A-I were associated with TG1 after incubation with whole blood + EDTA, EDTA–plasma, or EDTA–postheparin plasma. Significant amounts of unidentified apoproteins with molecular weights greater than 45 000 were also associated with these particles. Apoprotein E, apoprotein A-I, and a 51 000 dalton apoprotein were associated with the Sf > 400 fraction of TG2 recovered after incubation under the same conditions. The apoprotein profiles were indistinguishable from those previously reported for the corresponding Sf > 400 fraction recovered after intravenous infusion of TG1 and TG2. In the presence of Ca2+ and Mg2+ either in serum or in plasma and postheparin plasma, two additional proteins were recovered in the Sf > 400 fractions of TG1 and TG2. These apoproteins were of molecular weight 28 000 and 48 000 and had not been previously reported as components of plasma lipoproteins.