Differential uptake of D-galactosyl- and D-glucosyl-neoglycoproteins by isolated rat hepatocytes.

Bovine serum albumin was modified with 2-imino-2-methoxyethyl 1-thioglycopyranosides of galactose and glucose (Gal-AI-BSA, Glc-AI-BSA, respectively). Both types of neoglycoproteins were taken up by isolated rat hepatocytes. Gal-AI-BSA and Glc-AI-BSA inhibited the uptake of each other, and also inhibited the uptake of asialo-orosomucoid as expected from the results obtained with rabbit liver membranes (Stowell, C. P., and Lee, Y. C. (1978) J. Biol. Chem. 253, 6107-6110). Gal-neoglycoproteins of bovine serum albumin containing other linking groups between the galactose moiety and protein were found to be as effective in inhibition of the uptake of asialo-orosomucoid as Gal-AI-BSA, indicating that the method of carbohydrate attachment had little influence on endocytosis of galactose-terminated neoglycoproteins. In contrast, comparable Glc-neoglycoproteins (other than Glc-AI-BSA) were weak inhibitors. It thus appears that the positively charged amidino group present in Glc-AI-BSA contributes to the uptake of this neoglycoprotein by rat hepatocytes.