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Project 5 Prof. Oliver Einsle

Understanding Nitrogenase FeMo Cofactor

The element nitrogen is an essential constituent of all classes of biological macromolecules. In nature, the highly inert dinitrogen gas, N2, forms a natural sink for 99 % of all [N] cycling through the biosphere, so that nitrogen supply becomes a growth-limiting factor. Only a single enzymatic reaction is able to tap into the atmospheric reservoir, the one of the two-component metalloenzyme Nitrogenase.

In the Nitrogenase system, a 240 kDa component, the MoFe protein, contains two large and unique iron-sulfur clusters, the [8Fe:7S] P-cluster that serves as an electron transfer center, and FeMo cofactor, the active site of N2 reduction (Figure). FeMo cofactor is a heteronuclear metal site of composition [Mo:7Fe:9S:C]:homocitrate that is assembled ex situ and only inserted into apo-nitrogenase as a complete entity. The exact binding mode of substrate to the cluster, the site of binding, the electronic state of the individual metals and the overall reactivity of the center in the context of the enzyme are under heavy debate, but astounding progress was made in recent years.  

Nitrogenase has obvious relevance as the biological equivalent of the industrial Haber-Bosch process that today produces fertilizers that allow us to feed a major part of the world population, but at a cost of increasing nitrogen pollution. Harnessing the catalytic capacities of this enzyme thus holds the promise to move towards a new type of sustainable agriculture that is significantly more energy-efficient and environmentally friendly than current strategies.





Prof. Dr. Oliver Einsle

Institute of Biochemistry

Albertstr. 21

79104 Freiburg

Phone: +49 (0) 761 203-6058

Fax: +49 (0) 761 203-6161

email: einsle@bio.chemie.uni-freiburg.de



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