Apoproteins of human serum high density lipoproteins. Isolation and characterization of the peptides of Sephadex fraction V from normal subjects and patients with abeta-lipoproteinemia.

1. Sephadex fraction V, obtained from human serum high density lipoprotein apoprotein (HDL apoprotein) of normal subjects and of patients with abetalipoproteinemia, was resolved by DEAE-cellulose ion exchange column chromatography into several fractions which were defined in terms of amino acid composition, NH2- and COOH-terminsls, sialic acid content, immunologic and electrophoretic properties, and in vitro activation of purified lipoprotein lipase from rat adipose tissue. 2. Fraction V of HDL apoprotein of both normal and abetalipoproteinemic subjects was found to contain polypeptides corresponding to apolipoproteins C-I, C-II, C-III-1, and C-III-2, which had been described previously in very low-density lipoproteins (VLDL). The content of apo C-III-1 in abetalipoproteinemia-HDL was very low, whereas the percentage, by weight, of apo C-I was about twice as high as that in the normal subjects studied. Furthermore, both normal and abetalipoproteinemia-HDL apoprotein contained a previously unreported peptide which had a molecular weight of about 7 000 and electrophoretic, chemical, and immunological properties distinct from those of the known C apolipoproteins. Of all of the peptides comprising fraction V, only apo C-II activated a purified preparation of rat adipose tissue lipoprotein lipase. This was the case for both normal and abetalipoproteinemic subjects.