Maclura pomifera agglutinin or lectin (MPA/MPL) is tetrameric plant protein isolated from Osage orange. MPA has a molecular weight of about 44 kDa and consists of four subunits. There appear to be two different chains in combinations giving rise to five isolectins. The carbohydrate specificity of either type of subunit appears to be the same, preferring α-linked N-acetylgalactosamine structures. It has an isoelectric point between pH 4.8 and pH 5.3, and blood group specificity towards A, B, and O (-SA). This lectin has a high affinity for tumor-associated T-antigen disaccharide (Gal beta 1,3GalNAc alpha) and many O-linked glycopeptide structures. The structure of Gal beta 1,3GalNAc alpha occurs on the surface of tumor cells as a mucin-associated antigenic marker, termed as T-antigen. It is also the central element in O-linked glycopeptide structures on other mammalian glycoproteins.