Psophocarpus tetragonolobus lectin (PTL II, psophocarpin B1, a storage protein with chymotrypsin inhibitory activity), is isolated from winged bean seeds and purified by fractionation. The seed contains two lectins in which PTL II is the acidic of the two. This lectin agglutinates trypsinized and desialized erythrocytes of all three blood group types (A, B, and O). Nonpolar interactions play an important role in stabilization of the lectin-sugar complex. Projection of Î±1,3 linked Gal/GalNAc leads to steric hindrance and prevents the binding of blood group A and B reactive sugars.The unique specificity of PTL II makes it to be useful in isolation and characterization of terminally monofucosylated H-reactive oligosaccharides from those that are difucosylated or internally fucosylated.Cy3 can be used to visualize the binding pattern of Psophocarpus tetragonolobus Lectin (PTL/PTA II) in cellular imaging and flow cytometry. Cy3 is more photostable than many other fluorophores and can be seen with TRITC filter sets. It is commonly combined with green-fluorescent dyes for dual-labeling.