Narcissus pseudonarcissus (daffodil) lectin (NPL, NPA)

Daffodil lectin exists as a dimeric protein composed of two subunits of 13,000 daltons devoid of attached carbohydrate. Below pH 5.0 and above pH 9.0 NPL dissociates into monomers. This lectin has a specificity toward alpha linked mannose, preferring polymannose structures containing (a-1,6) linkages. Binding to mannose polymers can occur via internal mannose residues and is not dependent on structural integrity of a non-reducing end sugar. NPL also binds some galactomannans, and differs in other binding characteristics from a related lectin, Galanthus nivalis lectin. Unlike Con A, LCA and PSA, NPL does not bind glucose. 
Staining of the cytoplasmic membrane of cells with NPL after short-term acid treatment can indicate those cells undergoing apoptosis. Detection of apoptotic cells using NPL binding is a highly sensitive and reliable tool for studying cell death.