Figure 4: The oxyanion binding site in H. influenzae ASADH. Each of the oxyanion substrates and inhibitors interacts with the same protein ligands, Arg103 and Lys246, and is bound within attacking distance of the covalent acyl-enzyme intermediate. In the substrate structures with either phosphate or arsenate a second oxyanion molecule is bound to Ser100, Lys242, and Lys246 (figure adapted from reference [28]).