Structure of the ABO glycosyltransferase. Amino acid residues differing between blood group A and B-active transferases, respectively (Arg176Gly;Gly235Ser;Leu266Met;Gly268Ala) are shown with the single-letter code and their positions indicated. The 3-dimensional model was created with the DeepView Swiss Pdb Viewer version 3.7.