Nitrogenase Cofactor Centers On Carbon

A carbon atom sits in the middle of the iron-molybdenum cofactor in nitrogenase, the microbial enzyme that turns dinitrogen into ammonia, according to two reports in Science (DOI: 10.1126/science.1206445 and 10.1126/science.1214025). Understanding the components of nitrogenase and how it works may lead to better ways to make ammonia than the energy-intensive Haber-Bosch process. Crystal structures of nitrogenase first appeared in 1992, and research on the enzyme has shown that it uses an iron-sulfur cluster to transfer electrons to the Fe-Mo cofactor, where ammonia is likely produced. The cofactor incorporates one Mo, seven Fe, and nine S atoms surrounding a central atom believed to be C, N, or O, although the exact identity of the central atom remained unknown. Now, two groups, each with scientists from the U.S. and Germany, have used X-ray crystallography, spectroscopic techniques, and computational analysis to conclusively identify the central atom as carbon. The determination will be key to understanding the nitrogenase mechanism as well as how the cluster is biosynthesized, the authors say.