Further Observations on the Attachment of Carbohydrate to Lipoproteins by Rat Liver Golgi Membranes 1

Abstract

Summary

After in vitro incubation of rat liver Golgi membranes with ¹⁴C-CMP-sialic acid, the membranes were extracted by treatment with 2 × 10^–4 M Tris, pH 8.6, and lipoproteins were isolated by ultracentrifugation. The distribution of labeled lipoprotein was found to be 42% in VLDL, 14% in LDL, and 44% in HDL after sequential isolation of each density fraction. The addition of unlabeled whole rat serum to the extracted Golgi resulted in a decrease in label recovered in VLDL which was attributed to exchange of sialopeptides between VLDL and HDL. However, the addition of serum doubled the amount of recovered labeled lipoprotein and the extra label was associated with HDL. The labeled peptides were similar to those normally found in HDL as judged by DEAE-cellulose chromatography of the apo-HDL peptides. These results suggest the presence of a precursor pool of apolipoproteins within Golgi vesicles.