One Atom Makes All the Difference

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Science  18 Nov 2011:
Vol. 334, Issue 6058, pp. 914-915
DOI: 10.1126/science.1215283

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More than 100 years ago, Martin Beijerinck showed that pure cultures of the Azobacter bacterium could fix atmospheric nitrogen (N2). The enzymes responsible, the nitrogenases, break down the very strong triple bond in N2 to form ammonia (NH3); at least four types of nitrogenases have been isolated from Azobacter and other bacteria (1). It has long been hoped that molecular understanding of the nitrogenase enzymatic mechanism may lead to an enzymatic process to replace the high-pressure, high-temperature Haber process used commercially to convert nitrogen to ammonia. Yet despite intensive research, it remains unclear how nitrogenases efficiently catalyze the energy-intensive conversion of nitrogen to ammonia under ambient conditions. Two papers in this issue, by Lancaster et al. on page 974 (2) and by Spatzal et al. on page 940 (3), resolve a key structural detail that should help to elucidate the mechanism of the most widely studied type of nitrogenase, the molybdenum (Mo)–dependent nitrogenase.