Biophysical Studies of Metalloenzymes

Northwestern University, Evanston IL

Investigators

Abstract

Intellectual Merit Biological nitrogen fixation - the reduction of N2 to yield two moles of ammonia (NH3/ NH4+) that are available as plant nutrient - is catalyzed by the metalloenzyme, nitrogenase. The agronomic, economic, and social significance of nitrogenase can be appreciated by recognizing that the lives of about two-thirds of today's human population depend on plant growth, which relies on biologically fixed nitrogen generated by nitrogenase. The other third depends on nitrogen fixation by the industrial Haber-Bosch process, but this process is a significant component in the world's energy usage, demanding approximately 1 percent of human energy consumption. Whether the biological process can be more effectively exploited for human benefit remains an urgent question, and thus it is imperative that an understanding be achieved of the means by which organisms manage to activate and cleave N2 at ambient temperature and pressure. This project is addressing these questions through the use of electron-nuclear double resonance (ENDOR) and electron spin-echo envelope modulation (ESEEM) spectroscopies to characterize catalytic intermediates that form during the process of nitrogen fixation by nitrogenase. ENDOR/ESEEM studies uniquely provide information about the electronic properties of the substrate-binding/reduction active site, and supply detailed structural information regarding metal-bound substrates, intermediates, and products. No other technique offers this information. Broader Impact The outreach program associated with this project can be viewed (roughly) as a pyramid. At the apex are intellectual/scientific contributions to the discipline itself, and to the research community. Supporting these intellectual endeavors are contributions to the training of post doctoral scholars and graduate students, not only for this project but throughout the country and the world. The foundation level involves the encouragement of undergraduates and even high-school students, especially of women and underrepresented minorities, to participate in the scientific enterprise.