Accumulation of a nondegradable mannose ligand within rabbit alveolar macrophages. Receptor reutilization is independent of ligand degradation

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Abstract
Synthetic neoglycoproteins were made by reacting 5-(azidocarbonyl)pentyl 1-thio-.alpha.-D-mannopyranoside with poly(L-lysine) and poly(D-lysine). The 125I-Man90-poly-D-Lys and 125I-Man104-poly-L-Lys were tightly bound at 2.degree. C by the mannose receptor of the rabbit lung macrophage (Kd = 0.66 .+-. 0.18 and 0.59 .+-. 0.26 nM, respectively). Under saturating conditions in the cold, the macrophage bound 98,200 .+-. 7000 and 84,200 .+-. 10,500 ligand molecules per cell for the D- and L-polylysine derivatives, respectively. The cell-surface-bound ligands were dissociable by EDTA and mannose at 2.degree. C. At 37.degree. C, the macrophages internalized both 125I-Man90-poly-D-Lys and 125I-Man104-poly-L-Lys efficiently. Although the internalized 125I-Man104-poly-L-Lys was degraded quickly by the macrophage to small radiolabeled peptide, the internalized 125I-Man90-H-poly-D-Lys apparently could not be degraded or exocytosed. The amount of 125I-Man90-poly-D-Lys which accumulated within the cell was 7-fold higher than the combined amount of surface and intracellular mannose receptors, strongly indicating reutilization of the receptors independent of degradation of the ligand.