Metalloglycoprotein, containing Ca, Mg, Mn, and Zn and the carbohydrates galactose, glucosamine, mannose, and fucose. It agglutinates erythrocytes of blood group A1. Has a high preference for GalNAc over Gal. Homotetramer. Subunit II may arise from subunit I by proteolytic cleavage at the C-terminal end. Belongs to the leguminous lectin family.