Subcellular membrane topology and turnover of a rat hepatic binding protein specific for asialoglycoproteins

Abstract

Examination of the topological distribution of the rat liver binding protein specific for desialylated serum glycoproteins has revealed a subcellular distribution wherein this receptor is located largely, if not entirely, on the luminal membrane surface of the Golgi complex and smooth microsomes. In contrast, the receptor protein has been identified on the external, or cytosolic, surface of the lysosomal membranes. Recovery of the purified binding protein from whole rat livers established an average half-life survival time of approximately 88 h. Subsequently, injection in vivo of the readily catabolized ligand, asialo-orosomucoid, was found to be without effect upon the turnover rate of the receptor purified from isolated plasma membranes. These observations are interpreted as suggesting the existence of a recycling mechanism wherein the receptor is spared destruction in the lysosomes and remains available for subsequent reinsertion into the hepatocyte plasma membrane as part of a continuing process for the clearance of galactose-terminated ligands from the circulation.