Figure 23-20

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X-ray structure of murine adenosine deaminase in complex with its transition state analog 6-hydroxy-1,6-dihydropurine ribonucleoside (HDPR). The polypeptide is drawn in ribbon form colored according to its secondary structure (helices cyan, β strands magenta, and loops orange) and initially viewed approximately down the axis of the enzyme's α/β barrel from the N-terminal ends of its β strands. The HDPR is shown in stick form with C green, N blue, and O red. The enzyme-bound Zn2+ ion, which is coordinated by HDPR's 6-hydroxyl group, is represented by a silver sphere. Click the "Show Active Site Residues" button to view the amino acid side chains (with C gray, N blue, and O red) that interact with the HDPR molecule. [Based on an X-ray structure by Florante Quiocho, Baylor College of Medicine. PDBid 2ADA.]