Isolation and characterization of a receptor lectin specific for galactose/N-acetylgalactosamine from macrophages

Rat-peritoneal macrophages are shown to be able to take up glycoproteins terminated by galactose as well as those by mannose and/or N-acetylglucosamine. A lectin responsible for the uptake of galactose-terminated glycoproteins was isolated by affinity chromatography on a column of Sepharose 4B-asialoorosomucoid. The macrophage lectin isolated shared many properties in common with the well-established hepatic lectin specific for galactose/N-acetylgalactosamine. Thus, the lectin bound to asialoglycoproteins specifically, and the binding was inhibited by galactose and N-acetylgalactosamine. The lectin had a single major component of mol. wt. 42,000 as well as two minor components of 60,000 and 65,000, and required calcium for binding. In addition, the macrophage lectin was immunologically crossreactive with the hepatic lectin. Despite these similarities, however, the macrophage lectin was differentiated from the hepatic lectin in molecular size, relative preponderance of minor components, and titration profile with the antibodies raised against the hepatic galactose/N-acetylgalactosamine-specific lectin.