The dissociation in vitro of the α- and β-lipoprotein components of human and rat very low density lipoproteins

Heparin precipitates of human and rat serum lipoproteins, dissolved, dialyzed, and analyzed by paper electrophoresis, were found to migrate as β-lipoproteins. The pre-β-lipoproteins disappeared. Using specific anti-human β- and α-lipoprotein sera it was shown that the heparin precipitate of human very low density lipoproteins (VLDL) contained β-lipoproteins, whereas the supernatant contained α-lipoproteins. This indicates that these components are dissociated by the heparin precipitation procedure. Following partial delipidation of the heparin precipitate, a procedure which exposes the antigenic site of the α-lipoprotein of the VLDL, it can be demonstrated that the α-lipoprotein component is completely removed by the heparin precipitation procedure. Partially delipidated rat VLDL showed four immuno-reactive components when reacted against rabbit anti-rat VLDL serum, but only one, corresponding to the β-lipoprotein, when reacted with rabbit antiserum to heparin precipitate.Chemical analysis of the lipid components of the heparin precipitate and supernatant of human and rat VLDL reveals that over 90% of the triglycerides are precipitated by the heparin and that the supernatant fraction contains lipoproteins having a phospholipid to protein ratio higher than any of the other lipoproteins.Upon reincubation of the dissolved and dialyzed human serum heparin precipitate and its supernatant a pre-β band reappeared on paper electrophoresis. The recombined pre-β-lipoprotein was isolated and found to react with anti-β-, but not with anti-α-lipoprotein serum. This is a characteristic of native pre-β-lipoproteins. Evidence has also been obtained that the high density lipoproteins combine only with the β-lipoproteins originally present in the VLDL.