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 GalNAcα1-3Galβ1-4Glc.
Cy3 can be used to visualize the binding pattern of Psophocarpus tetragonolobus Lectin (PTL/PTA I) 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.