Fritz Haber 1868 1934 1918 Nobel prize synthesized

Fritz Haber 1868 - 1934 • 1918 Nobel prize “synthesized ammonia from its elements”

Annual Global N-fixation Data from various sources, compiled by DF Bezdicek & AC Kennedy, in Microorganisms in Action (eds. JM Lynch & JE Hobbie). Blackwell Scientific 1998.

Do not include taxa that fix N 2 Include taxa that fix N 2 Raymond et al 2004 Mol. Biol. Evol. 21: 541 -554 Possess homologs to Nif. H and Nif D but not known to fix N 2

Nitrogenase enzyme complex

Nitrogenase enzyme complex Mo. Fe protein • Dinitrogenase • Tetramer of two different dimers 2 2 heterodimer • = Nif. D, = Nif. K • Contains – Two Mo. Fe. S centers (active site for N 2 reduction) – Four Fe 4 S 4 centers • Combines N 2 and H+ to reduce N 2 to NH 3

Nitrogenase enzyme complex Mo. Fe protein NH 3 N 2 Fe protein 65 Å e- 190 Å From: Catalina Achim http: //www. chem. cmu. edu/groups/achim/research/magneto. html

Nitrogenase enzyme complex Fe protein • Dinitrogenase reductase • Dimer of two identical subunits 2 dimer • = Nif. H • Contains single Fe 4 S 4 center • Accepts reducing power (electrons) and reduces Mo. Fe protein (dinitrogenase)

Nitrogenase enzyme complex Mo. Fe protein NH 3 N 2 Fe protein 65 Å e- 190 Å From: Catalina Achim http: //www. chem. cmu. edu/groups/achim/research/magneto. html

Versatility of nitrogenase complex

Vesicles are the site of N 2 -fixation in Frankia. Nitrogenase reduces nitrogen using electrons and ATP from compounds donated by the plant (succinate is only one possibility). The product ammonia is most likely excreted from the vesicle where plant enzymes (GS) convert it to organic nitrogen (glutamine). (D. Benson)

Nitrogenase enzyme complex 2 ATP Ferredoxinoxidized Ferredoxinreduced Fered. eee- Feox. 2 ADP Mo. Feox. e- Mo. Fered. 2 Pi ee- 2 NH 3, H 2 N 2, 8 H+

Nitrogenase enzyme complex Mo. Fe protein NH 3 N 2 Fe protein 65 Å e- 190 Å From: Catalina Achim http: //www. chem. cmu. edu/groups/achim/research/magneto. html

Tree of Nif. H and Nif. D homologs Groups I - III possess functional nitrogenases Raymond et al 2004 Mol. Biol. Evol. 21: 541 -554

Two proposed nif gene vs. spp. trees (a) Last common ancestor (LCA) hypothesis (b) Methanogen origin hypothesis