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Figure 4.
Fig. 4. The binding of ascorbate. The structures have
been obtained on crystals soaked with ascorbic acid and
different inhibitors. Electron density maps as described for
Fig. 2. Water molecules are shown as red spheres. The refined
structures are shown, including ascorbate, water molecules,
sulfate ions, glycerol, inhibitors, and active site residues.
Hydrogen bonds involved in ascorbate recognition are shown as
dotted lines. a, soak with ascorbate, the glycerol molecule
comes from the cryoprotectant. b, ascorbate and
gluco-hydroximolactam. The ascorbate competes with the sulfate
ion that has both partial occupancies of 0.6 for the ascorbate
and 0.4 for the sulfate. c, ascorbate bound to the 2-F-glucosyl
enzyme. The water molecule that is activated by the ascorbate
for an attack on the C-1 carbon of the glucose is indicated by a
pink arrow.
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