Affinity purified Ulex europaeus agglutinin (UEA II) is isolated from gorse seeds and separated from crude extract. This lectin is a glycoprotein that consists of four 24,000 Da monomer subunits that require Ca2+ for binding to its ligands through carbohydrate recognition domain. It is specific for di-N-acetylchitobiose, an oligomer of GlcNAc. The monosaccharide GlcNAc is not an inhibitor of the lectin activity. UEA II has no mitogenic activity and agglutinates type O erythrocytes with greater interest than type A3 erythrocytes. Addition of EDTA eliminates agglutinating activity. Agglutinating activity can be recovered with the addition of calcium.UEA II is a potent inhibitor of the lectin complement pathway following endothelial oxidative stress. The molecular mechanism of UEA II-induced inhibition of the lectin complement pathway appears to be through competition for a common binding site on the endothelial cell and not at the level of mannose-binding lectin (MBL) inhibition. See other UEA II conjugates.Cy5, when bound to Ulex europaeus Lectin (UEA II), 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.