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.
Cy5, when bound to Bauhinia purpurea Lectin (BPL/BPA), can show the binding pattern of this lectin in cellular imaging and flow cytometry. The excitation wavelength required for Cy5 to fluoresce is high enough to avoid overlap with most other fluorochromes, making it useful for dual-labeling experiments. Because of this high excitation, there is typically less background from autofluorescence of biological specimens.