Bauhinia purpurea agglutinin or lectin (BPA/BPL) is a tetrameric lectin with a molecular weight of 195,000. Binding appears to be highest for glycoconjugates containing galactosyl (β-1,3)N-acetylgalactosamine structures but oligosaccharides with a terminal α-linked N-acetylgalactosamine can also bind. BPA is lactose-specific and elutes with the sugar lactose. It has specificity for blood groups A, B, O (-SA). Treatment of erythrocytes with neuraminidase or trypsin will increase the agglutination reaction, indicating that the receptor is masked by terminal carbohydrates.
Although binding specificity is similar to that of peanut agglutinin, tissue staining patterns of these two lectins are distinct. Makela's group 2 sugars, particularly N-acetyl-D-galactosamine, are potent inhibitors. The native protein appears to be stable in detergent solution.
Alkaline phosphatase (AP) is conjugated to Bauhinia purpurea Lectin (BPL/BPA) to show the binding of BPL/BPA 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.