"If we can understand the mechanism of nitrogenase, we may not only figure out why nature evolved it to be such a complex enzyme, but we might also uncover design principles for ammonia production in a more cost-effective and environmentally friendly fashion," stated Tezcan.Īlthough much is known about the structure of nitrogenase, until now, no one has been able to acquire atomic-resolution images of the enzyme while "turning over" or in the process of catalyzing atmospheric nitrogen into ammonia, largely due to technological limitations.Īlthough scientists can obtain atomic-resolution images of proteins using X-ray crystallography, this method requires the proteins to be fixed in place within a crystal - stationary in a sense - which means that it cannot capture nitrogenase in action. How does the enzyme catalyze nitrogen reduction at ambient temperatures and pressure whereas the industrial process requires such extreme conditions? The process also raises environmental concerns including leaching of nitrates into groundwater and higher emissions of the greenhouse gas nitrous oxide.Ī key question that drives biological nitrogen-fixation research is the contrast between nitrogenase and the Haber-Bosch process. An estimated 1-2% of all global energy production is consumed by the Haber-Bosch process. However, the Haber-Bosch process is very energy-intensive, requiring temperatures exceeding 400☌ and high pressures of hydrogen gas. The Haber-Bosch process has often been cited as the driving factor behind the world's population explosion over the past century, having "turned air into bread." Industrially produced ammonia is largely used for fertilizers, and its advent revolutionized agricultural practices in the first half of the 20 th century. Nitrogenase was the essentially the only source of fixed nitrogen in the biosphere until the advent of the Haber-Bosch process - the industrial procedure for converting atmospheric nitrogen to ammonia - more than a hundred years ago. However, most living organisms do not possess the nitrogenase enzyme and cannot metabolize atmospheric nitrogen into a bioprocessable form. All organisms require "fixed" sources of nitrogen for the biosynthesis of life's building blocks such as proteins and DNA. Understanding the significance of these cryoEM images requires understanding the tremendous global importance of nitrogen fixation. It opens the doors to fully understanding the mechanism of this enigmatic enzyme, which has preoccupied researchers for decades."
"To be able to obtain atomic-level-resolution pictures of an enzyme as dynamic and complex as nitrogenase in action is extremely exciting. "This is a very important advance in terms of biological nitrogen fixation as well as structural biology, in general," stated Tezcan. While Tezcan has long studied nitrogenase, Herzik provided the cryoEM expertise needed to carry out the research. This work was accomplished through a close partnership between the groups of Professor Akif Tezcan and Assistant Professor Mark Herzik, both in UC San Diego's Department of Chemistry and Biochemistry.
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