Evolutionary considerations on the thermodynamics of nitrogen fixation.
An evolutionary explanation is sought for the fact that ATP is needed for N2 fixation in spite of the exergonicity of the process. After a survey of the state of knowledge about the thermodynamics of N2 fixation in fermenters, photosynthesizers and respirers it is suggested that nitrogenase, which still shows ATP-dependent hydrogenase activity, evolved from an ATP-requiring hydrogenase that lacked nitrogenase activity. The hydrogenase action in the Archaean, reducing, biosphere may have needed ATP to ensure expulsion of H2. Extant non-nitrogenase hydrogenases have lost the dependence on ATP. Because of its complexity, nitrogenase could not rid itself of the ATP dependence or of hydrogenase activity, both wasteful. Presumably all hydrogenases evoled from ferredoxin-like Fe-S proteins.
D001419:Bacteria / Q000235:genetics; D005075:Biological Evolution; D000458:Cyanobacteria / Q000235:genetics; D005288:Ferredoxins / Q000235:genetics; D008433:Mathematics; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000235:genetics; D010788:Photosynthesis; D010944:Plants / Q000235:genetics; D013816:Thermodynamics
D005288:Ferredoxins; D009591:Nitrogenase