Fig. 5. (A) Stereoview of the final 1.7 Å, σA-weighted (Read, 1986) 2F_o – F_c electron density map contoured at 1.25 σ, superimposed on the active site region of the final estranged-G model. (B) Active site region of the enzyme. The C-N bond of the reduced Schiff base is shown in pink. Contacts between the 3′-phosphate and the amide protons of Gln42 and Thr140, and between the 5′-phosphate and the amide proton of Asp45 are not shown explicitly, for reasons of illustrative clarity. The positions of the C2′ protons, though not visible in experimental electron density maps, are inferred from the geometry of the heavy atom backbone. (C) Structural superimposition of the non-covalent complex (THF-Iodine1) onto the covalent estranged-G complex. The non-covalent complex is coloured similarly to (B) and the covalent complex (estranged-G) is dark grey.