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Assimilatory nitrate reduction is the rate-limiting step in nitrogen acquisition in higher plants, algae, and fungi under many conditions and therefore plays a key role in global nitrogen cycling. On pages 1167-1179, Fischer et al. present the long-awaited high-resolution crystal structure of the nitrate-reducing molybdenum-containing fragment of eukaryotic nitrate reductase. The cover image shows a ribbon diagram of the nitrate reductase molybdenum-containing domain from the yeast Pichia angusta. Two crystal structures of this dimeric enzyme were determined at 1.7- and 2.6- resolution. Based on conformational changes and water molecules in the active site, the binding of nitrate, a penta-coordinated reaction intermediate, and product release were proposed. The magnifying glass highlights the active site, with the approaching nitrate ending up as reaction intermediate and displacing the molybdenum-coordinated hydroxyl group. Because yeast nitrate reductase is representative of the family of eukaryotic nitrate reductases, the structural model is of global relevance.
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