Psophocarpus tetragonolobus lectin (PTL I, psophocarpin B1, a storage protein with chymotrypsin inhibitory activity), is isolated from winged bean seeds and purified by affinity chromatography. The seed contains two lectins in which PTL I is the basic of the two. PTL I is a dimeric glycoprotein with specificity to GalNAc, with eluting sugar GalNAc. This lectin agglutinates trypsinized rabbit and human erythrocytes (type A and B) but not trypsinized human type O erythrocytes. PTL I recognize blood group A-substance derived oligosaccharides such as trisaccharide GalNAcÎ±1-3GalÎ²1-4Glc. 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 Psophocarpus tetragonolobus Lectin (PTL/PTA I). Colloidal gold labeled lectins can be viewed via electron microscopy.