Interaction of transferrin with rat alveolar macrophages.
Binding of rat transferrin to isolated alveolar macrophages was investigated in the 0.125 nM to 2 microM range. Computer analysis of the data revealed two classes of binding sites, a small number (< 1000 exposed/cell) having high affinity (dissociation constant (Kd), 3.4 nM) and a large number (approximately 4 x 10(6)/cell) having low affinity (Kd 48 microM). Measurements with a monoclonal antibody to the rat transferrin (rTf) receptor yielded values in the same range as the high-affinity sites derived from studies of ligand binding. Binding to the low-affinity sites at pH 5.8 was nearly one order of magnitude stronger than that at pH 7.3. Bovine lactoferrin (12 microM), cationized bovine serum albumin (14 microM), L-arginine (50 mM), and L-lysine (50 mM) did not compete against rTf binding to the low-affinity sites. Removal of an average of 2.6 x 10(8) sialyl residues from each cell did not affect binding. Heparan sulphate proteoglycan purified from alveolar macrophages bound strongly to immobilized rTf, thus raising the possibility that the low-affinity interaction of transferrin with these cells may be mediated, at least in part, by this glycosaminoglycan.
Janicka
M
M
Department of Pathology, McMaster University Health Sciences Centre, Hamilton, ON, Canada.
Regoeczi
E
E
Bolyos
M
M
Hu
W L
WL
D000818:Animals; D001059:Apoproteins / Q000378:metabolism; D001665:Binding Sites; D002417:Cattle; D005290:Ferric Compounds / Q000378:metabolism; D006497:Heparan Sulfate / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D016676:Macrophages, Alveolar / Q000378:metabolism*; D019158:N-Acetylneuraminic Acid; D051381:Rats; D011990:Receptors, Transferrin / Q000378:metabolism*; D012794:Sialic Acids / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism*
D001059:Apoproteins; D005290:Ferric Compounds; D006497:Heparan Sulfate; D019158:N-Acetylneuraminic Acid; D011990:Receptors, Transferrin; D012794:Sialic Acids; D014168:Transferrin