Abstract
A lectin in rat alveolar macrophage membranes with a high affinity for binding ligands containing L-fucose and N-acetyl-D-glucosamine has been isolated by affinity chromatography on Fuc-BSA-Sepharose (where Fuc is fucosyl and BSA is bovine serum albumin). The lectin was extracted from rat lung homogenates with Triton X-100, absorbed from the extract onto Fuc-BSA-Sepharose in the presence of Ca2+ and eluted by removal of Ca2+. After a second adsorption to and elution from Fuc-BSA-Sepharose, three protein species were detected electrophoretically in fractions that bind Fuc-BSA. One, which was the mannose/N-acetylglucosamine lectin (Mr = 32,000) found earlier in hepatocytes, was removed by adsorption on anti-lectin IgG-Sepharose. Another (Mr = 46,000) was removed by adsorption to Fuc-BSA-Sepharose and elution with galactose. The remaining lectin (Mr = 180,000) bound fucose and N-acetylglucosamine but not galactose. Binding was maximal between pH 6.5 and 9.0 and dependent on Ca2+. Immunocytological analysis with rabbit anti-lectin IgG and fluorescein-labeled goat anti-rabbit IgG revealed the lectin to be in rat alveolar macrophages and nonparenchymal cells of liver. Thus, the lectin appears to be present in macrophages and is likely involved in receptor-mediated endocytosis. It is distinctly different structurally from the hepatocyte lectin with a similar ligand-binding specificity.
Highlights
A lectin in rat alveolar macrophage membranweisth chain, which contains an asparaginyl-linked oligosaccharide a highaffinity for binding ligands containing L-fucosaend is on the external surface of the cell
We wish to report here the isolation and partial characterthe lectin appears to be present in macrophages ainsd ization of a lectin from rat alveolar macrophages that has a likely involved in receptor-mediated endocytosiIst. is M, = 180,000 and an oligosaccharidebinding specificity very distinctly different structurally from the hepatocyte similar to that of receptors on macrophages [15, 16]
The first to be affinity for Fuc-BSA’ anda molecular weight of about discovered in mammals has two types of polypeptide subunits 180,000,a value similar to thatfound by others for a lectin in (Mr= 42,000 and 48,000) ( l ), binds oligosaccha- alveolar macrophages [17], it was possible that this macrorides with nonreducing terminal galactose or N-acetylgalac- phage lectin may be present in nonparenchymal cells of tosamine [2], andis a transmembrane proteinof hepatocytes liver
Summary
We wish to report here the isolation and partial characterthe lectin appears to be present in macrophages ainsd ization of a lectin from rat alveolar macrophages that has a likely involved in receptor-mediated endocytosiIst. is M , = 180,000 and an oligosaccharidebinding specificity very distinctly different structurally from the hepatocyte similar to that of receptors on macrophages [15, 16]. The first to be affinity for Fuc-BSA’ anda molecular weight of about discovered in mammals has two types of polypeptide subunits 180,000,a value similar to thatfound by others for a lectin in (Mr= 42,000 and 48,000) ( l ) , binds oligosaccha- alveolar macrophages [17], it was possible that this macrorides with nonreducing terminal galactose or N-acetylgalac- phage lectin may be present in nonparenchymal cells of tosamine [2], andis a transmembrane proteinof hepatocytes liver. Tocytes [7].It has asmaller polypeptide subunit (Mr= 25,000), and binds N-acetylglucosamine and mannose [7]
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