Editing Nitrogen fixation (section)

=== Evolution of nitrogenase ===
Nitrogenase is thought to have evolved sometime between 1.5-2.2 billion years ago (Ga),<ref>{{Cite journal |last1=Garcia |first1=Amanda K. |last2=McShea |first2=Hanon |last3=Kolaczkowski |first3=Bryan |last4=Kaçar |first4=Betül |date=May 2020 |title=Reconstructing the evolutionary history of nitrogenases: Evidence for ancestral molybdenum-cofactor utilization |journal=Geobiology |language=en |volume=18 |issue=3 |pages=394–411 |doi=10.1111/gbi.12381 |issn=1472-4677 |pmc=7216921 |pmid=32065506|bibcode=2020Gbio...18..394G }}</ref><ref>{{Cite journal |last1=Boyd |first1=E. S. |last2=Anbar |first2=A. D. |last3=Miller |first3=S. |last4=Hamilton |first4=T. L. |last5=Lavin |first5=M. |last6=Peters |first6=J. W. |date=May 2011 |title=A late methanogen origin for molybdenum-dependent nitrogenase |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1472-4669.2011.00278.x |journal=Geobiology |language=en |volume=9 |issue=3 |pages=221–232 |doi=10.1111/j.1472-4669.2011.00278.x |pmid=21504537 |bibcode=2011Gbio....9..221B |issn=1472-4677}}</ref> although some isotopic support showing nitrogenase evolution as early as around 3.2 Ga.<ref>{{Cite journal |last1=Stüeken |first1=Eva E. |last2=Buick |first2=Roger |last3=Guy |first3=Bradley M. |last4=Koehler |first4=Matthew C. |date=April 2015 |title=Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr |url=https://www.nature.com/articles/nature14180 |journal=Nature |language=en |volume=520 |issue=7549 |pages=666–669 |doi=10.1038/nature14180 |pmid=25686600 |bibcode=2015Natur.520..666S |issn=0028-0836}}</ref> Nitrogenase appears to have evolved from [[maturase]]-like proteins, although the function of the preceding protein is currently unknown.<ref>{{Cite journal |last1=Garcia |first1=Amanda K |last2=Kolaczkowski |first2=Bryan |last3=Kaçar |first3=Betül |date=2022-03-02 |editor-last=Archibald |editor-first=John |title=Reconstruction of Nitrogenase Predecessors Suggests Origin from Maturase-Like Proteins |journal=Genome Biology and Evolution |language=en |volume=14 |issue=3 |doi=10.1093/gbe/evac031 |issn=1759-6653 |pmc=8890362 |pmid=35179578}}</ref>

Nitrogenase has three different forms (''Nif, Anf, and Vnf'') that correspond with the metal found in the active site of the protein (molybdenum, iron, and vanadium respectively).<ref>{{Cite journal |last=Eady |first=Robert R. |date=1996-01-01 |title=Structure−Function Relationships of Alternative Nitrogenases |url=https://pubs.acs.org/doi/10.1021/cr950057h |journal=Chemical Reviews |language=en |volume=96 |issue=7 |pages=3013–3030 |doi=10.1021/cr950057h |pmid=11848850 |issn=0009-2665}}</ref> Marine metal abundances over Earth's geologic timeline are thought to have driven the relative abundance of which form of nitrogenase was most common.<ref>{{Cite journal |last1=Anbar |first1=A. D. |last2=Knoll |first2=A. H. |date=2002-08-16 |title=Proterozoic Ocean Chemistry and Evolution: A Bioinorganic Bridge? |url=https://www.science.org/doi/10.1126/science.1069651 |journal=Science |language=en |volume=297 |issue=5584 |pages=1137–1142 |doi=10.1126/science.1069651 |pmid=12183619 |bibcode=2002Sci...297.1137A |issn=0036-8075}}</ref> Currently, there is no conclusive agreement on which form of nitrogenase arose first.