Receptor-Mediated Endocytosis of Mannose-Terminated Glycoproteins in Hepatocytes

The parenchymal cells of the liver contain more than 90% of the total hepatic binding capacity for glycoproteins terminating in mannose or N-acetylglucosamine [1, 2]. It was thought that all of this binding capacity was intracellular; mannose-specific uptake of glycoproteins by hepatocytes was suspected [3, 4], but it was not definitely shown to occur until recently [5]. In order to obtain detailed evidence for the receptor-mediated endocytosis of mannose-terminated proteins in hepatocytes, we used a glycoprotein ligand with a high molecular weight: yeast invertase. It contains about 50% mannose by weight in several large polymannose chains which are attached to the peptide via two N-acetylglucosamine residues [6, 7].