The Associating System of Small Subunits in ApoLDL

Abstract

There is controversy about the size and composition of the protein moiety from human low density lipoprotein (LDL, density range 1.019-1.063 g/ml). Bradley et al. (1978) reported results from the partial sequence of CNBr-peptides of apoLDL indicating that the molecular weight was 30,000. Huang and Lee (1979), using a preparation of apoLDL extracted with ether-ethanol, detected polypeptides with molecular weights from 69,000 to 136,000. However, Steele and Reynolds (1979) found that apoLDL delipidated with sodium dodecyl sulfate (SDS) was made of a single component with molecular weight above 200,000 and postulated that proteolysis caused the presence of small components observed upon aging. On the other hand, neither Bradley et al. (1978) nor Huang and Lee (1979) were able to detect the production of new N-terminal amino acids in their preparations. Goldstein and Chapman (1979) examined the competition of peptides, obtained by trypsin digestion of LDL, for the binding sites in antibodies prepared against LDL, indicating that repetition of antigenic sites on the peptides is suggestive of recurrence of similar subunits in apoLDL.