| Abstract: | The nature of the hepatic receptors that bind glycoproteins through fucose at the non-reducing termini of oligosaccharides in glycoproteins has been examined by three different approaches. First, the clearance from blood of intravenously injected glycoproteins was examined in mice with the aid of neoglycoproteins of bovine serum albumin (BSA). The clearance of fucosyl-BSA was rapid and was not strongly inhibited by glycoproteins that inhibit clearance mediated by the galactose or the mannose/N-acetylglucosamine receptors of liver. The clearance of Fuc alpha 1,3(Gal beta 1,4)GlcNAc-BSA (where Fuc is fucose) was inhibited weakly by either Fuc-BSA or Gal beta 1,4GlcNAc-BSA but strongly by a mixture of the two neoglycoproteins, suggesting that its clearance was mediated by hepatic galactose receptors as well as by a fucose-binding receptor. Second, the binding of neoglycoproteins to a membrane fraction of mouse liver was examined. Fuc-BSA binding to membranes was Ca2+ dependent but was not inhibited by glycoproteins that would inhibit the galactose or the mannose/N-acetylglucosamine receptors. In addition, the binding of Fuc-BSA and Gal beta 1,4GlcNAc-BSA differed as a function of pH, in accord with binding of Fuc-BSA through fucose-specific hepatic receptors. Finally, the binding of neoglycoproteins to the pure galactose lectin from rat liver was examined. Neither Fuc-BSA nor Fuc alpha 1,2Gal beta 1,4GlcNAc-BSA bound the galactose lectin, although Fuc alpha 1,3(Gal beta-1,4) GlcNAc-BSA bound avidly. Taken together, these studies suggest that a fucose-binding receptor that differs from the galactose and the mannose/N-acetylglucosamine receptors may exist in rat and mouse liver. |
