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.
Alkaline phosphatase (AP) is conjugated to Psophocarpus tetragonolobus Lectin (PTL/PTA I) to show the binding of PTL/PTA I in many applications including Western blotting and ELISA. Alkaline phosphatase is a large protein (140 kDa) that catalyzes the hydrolysis of phosphate groups from a substrate resulting in a colored or fluorescent product. The optimal enzymatic activity of this protein is between pH 8 and 10, and its reaction rate remains linear, improving sensitivity over time.