L-Fucose-terminated glycoconjugates are recognized by pinocytosis receptors on macrophages

¹²⁵I-Labeled L-fucose-albumin complex and rat preputial β-glucuronidase are rapidly cleared from plasma after intravenous infusion. L-Fucose-albumin retards the plasma clearance of β-glucuronidase whereas D-fucose-albumin is inactive. In vitro, ¹²⁵I-labeled L-fucose-albumin is taken up into rat or rabbit alveolar macrophages by receptor-mediated pinocytosis. Uptake (37°C) is time-dependent, is saturable with increasing ligand concentration (K(uptake) = 4.4 x 10^-8M), and requires Ca²⁺. ¹²⁵I-Labeled D-fucose-albumin is poorly taken up. Binding (4°C) is saturable and Ca²⁺ dependent. Binding and uptake are fully inhibited by yeast mannan. A series of neoglycoproteins, including L-fucose-albumin, were tested as inhibitors of uptake of ¹²⁵I-labeled β-glucuronidase into macrophages. The following order of potency was observed: L-Fuc= D-Man>GlcNAc nearly equal to D-Glc>D-Xyl >>>D-Gal=L-Ara=D-Fuc. L-Fucose-terminated oligosaccharides coupled to bovine serum albumin also block ¹²⁵I-labeled β-glucuronidase uptake into macrophages.