1QEZ:
reference: Sulfolobus acidocaldarius inorganic pyrophosphatase: structure, thermostability, and effect of metal ion in an archael pyrophosphatase., Leppanen VM, Nummelin H, Hansen T, Lahti R, Schafer G, Goldman A, Protein Sci 1999 Jun;8(6):1218-31. PMID: 10386872

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