Griffonia simplicifolia lectin (GSL I) is affinity purified from a woody climbing shrub native to Africa. GSL I is composed of two types of subunits A and B that combine to form tetrameric structures, resulting in five isolectins. This lectin has affinity for terminal Î±-D-galactosyl residues and terminal N-acetyl-Î±-D-galactosaminyl residues. The A-rich lectin preferentially agglutinates blood group A erythrocytes and thus appears to be specific for Î±-N-acetylgalactosamine residues, while the B-rich lectin preferentially agglutinates blood group B cells and is specific for Î±-galactose residues. This lectin shows specificity for blood group B greater than blood group A1.GSL I has been reported to bind several glycoproteins including laminin. Since some Î±-D-galactosyl residues are expressed in endothelial cells of mouse tissues, GSL I can present a highly specific surface of glycosylation pattern in these cells.Colloidal gold can be used to visualize localization of specific saccharide moieties and examine the distribution of plasma membrane glycoproteins based on the binding pattern of Griffonia simplicifolia Lectin (GSL I). Colloidal gold labeled lectins can be viewed via electron microscopy.