Antibodies to hepatic endosomes. Identification of two endosome antigens

Endosome fractions were prepared from rat liver homogenates, and antibodies were raised in rabbits against the integral membrane proteins. Immunofluorescent studies showed that these antibodies identified primarily intracellular structures in liver sections, isolated hepatocytes and HepG-2 cells. Immunoelectron microscopy using protein A-gold confirmed that endocytic multivesicular structures, especially those located at the biliary pole of the hepatocyte, were labeled. Biochemical analysis showed that approximately 12 endosome antigens were present. A major 43 kDa glycosylated antigen corresponded to the asialoglycoprotein receptor subunit. A further antigen identified in endosomes was a 115 kDa polypeptide pI 4.3 previously identified as a major calmodulin-binding protein. The antigens identified in rat liver endosomes were different to those previously shown by other studies to be present in the Golgi apparatus and lysosomes.