Characterization of a mannose and N-acetylglucosamine-specific lectin present in rat hepatocytes

We have isolated and characterized a Man/GlcNAc-specific lectin from rat liver. The specificity of this lectin resembles that of the previously reported Man/GlcNAc-specific receptor activity present on the surface of hepatic reticuloendothelial cells when tested with simple sugars, but can be distinguished from the latter by utilizing characterized glycopeptides and glycoproteins. The lectin isolated from liver originates predominantly from hepatocytes rather than reticuloendothelial cells. It is found in microsomes upon subcellular fractionation and is not expressed on the surface of isolated hepatocytes. In addition, specific antisera to the lectin do not prevent endocytosis by hepatic reticuloendothelial cells. The lectin can be solubilized by treatment of whole liver or isolated hepatocyte homogenates with buffers containing 0.2 M NaCl in the absence of any detergent, indicating that it may be either a soluble protein or a peripheral membrane protein. Based on the physical properties, oligosaccharide specificity, and subcellular location, this lectin does not appear to be the same as the Man/GlcNAc-specific activity which mediates endocytosis by hepatic reticuloendothelial cells and presumably has a different function.