GSL I is a family of glycoproteins with molecular weights of approximately 114 kDa. There are two types of subunits, termed “A” and “B”, with slightly different molecular weights. These subunits combine to form tetrameric structures, resulting in five isolectins. The “A”-rich lectin preferentially agglutinates blood group A erythrocytes and thus appears to be specific for α-N-acetylgalactosamine residues, while the “B”-rich lectin preferentially agglutinates blood group B cells and is specific for α-galactose residues. Our GSL I is a mixture of the five isolectins. GSL I has been reported to bind several glycoproteins including laminin.