Epithelial Rat Liver Cells Have Cell Surface Receptors Recognizing a Phosphorylated Carbohydrate on Lysosomal Enzymes

Abstract

Receptor-mediated endocytosis of .alpha.-N-acetylglucosaminidase by cultured epithelial rat liver cells is inhibited by mannose, L-fucose and most effectively by mannose 6-phosphate. Endocytosis of .alpha.-N-acetylglucosaminidase is lost after treatment of the enzyme with alkaline phosphatase. Epithelial rat liver cells apparently possess cell surface receptors that recognize a phosphorylated carbohydrate on .alpha.-N-acetylglucosaminidase, as was previously reported for cell surface receptors of human skin fibroblasts. Inhibition of .alpha.-mannosidase endocytosis by epithelial rat liver cells in the presence of mannose 6-phosphate and loss of enzyme endocytosis after treatment with alkaline phosphatase suggest that this enzyme is recognized by the same receptor.