GSL I is a family of glycoproteins with molecular weights of ~114kD. 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.