Biochemical features and functional activity of the endocytic compartment in the liver cell

When many ligands, polypeptidic hormones, growth factors, metabolic carriers, plasma glycoproteins, etc., bind to cell-surface receptors, ligand-receptor complexes are internalized by a process called receptor-mediated endocytosis towards the endocytic compartment. The endocytic compartment is an extensive network of anastomosing vesiculo-tubular membranes that differs biochemical and functionally from other intracellular organelles. Endosome fractions were prepared and antibodies raised against endosome membrane proteins. In addition to a detailed biochemical study of proteins and glycoproteins the antibodies were used to immunolocalize the endocytic structures in the hepatic cell. These studies aided to demonstrate the involvement of endocytic compartment not only in the sorting of proteins to specific domains of the plasma membrane but in the identification of "resident" endosome components.