Evidence for the lipoprotein heterogeneity of human plasma high density lipoproteins isolated by three different procedures

Abstract Quantitative electroimmunoassays of apolipoproteins in ultracentrifugally isolated high density lipoproteins (HDL) of normolipidemic subjects showed that A‐I and A‐II are the major (80–85% of total HDL protein) and B, C‐III, E, D and F are the minor protein constituents of this density class. A comparison between the apolipoprotein composition of ultracentrifugally isolated HDL and heparin‐Mn ++ supernates showed no significant difference in the levels of A‐I and C‐III. However, the concentration of ApoE in the heparin‐Mn ++ supernates was almost twice as high as that in the ultracentrifugally isolated HDL; ApoB was only detectable in trace amounts in the heparin‐Mn ++ supernates. To establish whether these apolipoproteins are parts of a single macromolecular complex or form separate, discrete lipoprotein particles, the high density lipoproteins were isolated by three different procedures including ultracentrifugation, heparin‐Mn ++ precipitation and agarose column chromatography. The double diffusion analyses of each of these HDL preparations with antisera to A‐I, A‐II, ApoB, C‐III, ApoD, ApoE, and ApoF showed nonidentity reactions between each possible combination of these antisera. The only exception was a reaction of partial identity between antisera to A‐I and A‐II polypeptides indicating the occurrence of two types of lipoprotein particles, a major one (LP‐A) containing both polypeptides and a minor one (LP‐A‐I) containing A‐I as the sole protein constituent. These findings indicate that high density lipoproteins, regardless of the manner of isolation, do not consist of a single macromolecular complex, but represent a mixture of several, discrete lipoprotein families.