Figure 11-13a

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Human carbonic anhydrase. The Zn2+ ion (cyan sphere) is shown tetrahedrally liganded to three invariant His sidechains (N blue, C green). Note that the bicarbonate ion product, which is shown in ball-and-stick form, forms the fourth ligand with the Zn2+. The bicarbonate ion is in a hydrogen-bonded network involving Thr 199 and Glu 106, as can be highlighted by clicking alternately on the "Hide H-bonds" and "Show H-bonds" buttons. [Based on the X-ray structure by K. K. Kannan, Bhabha Atomic Research Center, Bombay, India, PDBid 1HCB]