Biosynthesis of plasma lipoproteins by rat liver ribosomes.

Rat liver ribosomes in uifro incorporated labeled amino acids into proteins which showed the immunological behavior of the plasma lipoproteins. The presence of carrier lipoprotein or carrier lipid was required for the isolation and ultracentrifugal purification of immunologically reactive, labeled low and high density lipoproteins. The identity of the lipoproteins was further characterized by solubility criteria and a peptide-mapping technique. A high correlation between the peptide labeling patterns of ribosome-labeled and slice-labeled preparations was found. It is suggested that rat liver ribosomes in uifro are capable of synthesizing the protein moieties of the plasma lipoproteins. These apoproteins are then capable of binding lipid. Rat liver mitochondria and rat kidney ribosomes in vifro were also capable of incorporating radioactive amino acids into lipoproteins, but these proteins were immunologically different from the plasma lipoproteins.