This study was designed to identify a method for the measurement of human high density lipoprotein subfraction (HDL 2 and HDL 3) metabolism. Apolipoproteins A-I, A-II, and C, the major HDL apoproteins, were radioiodinated and incorporated individually into HDL 2 and HDL 3 in vitro. Using a double label technique, the turnover of apoA-I in HDL 2 and HDL 3 was measured simultaneously in a normal male. The apoprotein exchanged rapidly between the two subfractions evidenced by equilibration of their apoA-I specific activity. Radiolabeled apoA-II, incorporated into the subfractions, showed a similar exchange in vitro. Incubation of 131I-labeled very low density lipoproteins (VLDL) with HDL or its subfractions resulted in transfer of C proteins from VLDL to the HDL moiety. The extent of transfer was dependent on the HDL subfraction present; 50% of the VLDL apoC was transferred to HDL 3, while the transfer to total HDL and HDL 2 was 69% and 78%, respectively. ApoC also exchanged between HDL 2 and HDL 3, again showing a preference for the former and suggesting a primary metabolic relationship between VLDL and HDL 2. Overall, the study indicates that apoA-I, apoA-II, and the C proteins exist in equilibrium between HDL 2 and HDL 3. This phenomenon precludes their use as probes for HDL subfraction metabolism in humans.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of lipid research|
|State||Published - 1978|
ASJC Scopus subject areas
- Cell Biology