Amaranthus caudatus lectin or agglutinin (ACL/ACA) is isolated from tassel flower seeds. This lectin is present in seeds only and not in stems or in leaves.

Amaranthus caudatus Lectin (ACL) is a homo-dimer composed of two 35 kDa subunits. Isoelectric focusing of the lectin resolves it into four bands with isoelectric points between pH 6.7 and pH 7.7. Unlike most lectins, it binds best in mildly acidic conditions. ACL also does not appear to require divalent cations for activity.

This lectin preferentially binds to oligosaccharides containing Gal-beta-3GalNAc, with an eluting sugar of desialyzed fetuin. ACL tolerates sialic acid substitution at the 3 position of galactose in the « T » antigen. It does not have specificity for blood groups but does have a higher affinity for type O erythrocytes over B and A.