Fe cycle

Seefeldt and Dean7 describe the nitrogenase enzyme s so-called Fe cycle in the following steps ... 

Ewers WE (1983) Chemical factors in the deposition and diagenesis of banded iron-formation. In Iron Formations Facts and Problems. Trendall AF, Morris RC (eds) Elsevier, Amsterdam, p 491-512 Fantle MS, DePaolo DJ (2002) The isotopic composition of continental iron and implications for the global Fe cycle. EOS Trans Am Geophys Union 83 V22B-1234... 

The reductive portions of the N, S, and Fe cycles are driven by chemical energy fixed in organic substances during photosynthesis. The chemolithotrophic reoxidation of N, S, and Fe is, in turn, linked to the conversion of CO2, into cell material, again involving the cycling of C, H, and O. This is shown in Figure 7.10. 

The Westinghouse cycle has many advantages widely reported and discussed in the literature. However, it is known that the Westinghouse cycle is hampered by the low water solubility of SO2 and challenges presented by the acidity of the SO2 electrolytic oxidation process [15]. To date, many efforts have been made to improve the efficiency of the electrolytic process for oxidation of SO2. Prior work has involved the use of a depolarized electrolyzer as well as addition of a third process step - examples include S-I, S-Br and S-Fe cycles given below ... 

The role of ectoenzymes in Fe cycling is not known presently, but we have some evidence of Fe(III) reduction in phytoplankton cultures, and Fe(III) complexes are reduced by plasmamembrane reductases. Hydrogen peroxide can oxidize Fe(II) (Waite and Morel, 1984) and probably reduce Fe(III) in light, thus implying that the biota may promote this reaction through the activity of their extracellular enzymes. 

Beard, D.L., Johnson, C.M., Von Damm, K.L. and Poulson, R.L., 2003. Iron isotope constraints on Fe cycling and mass balance in oxygenated Earth oceans. Geology, 31 629-632. 

Pulsed radiolysis studies indicate that the reaction proceeds via two sequential steps, both first order in 02 , in which O2 is alternately oxidized to O2 or reduced to H2O2 by the Fe ion. Thus, the Fe cycles between the III and II states. Fe SOD takes up a proton upon reduction throughout the pH range of activity, and chemical precedent as well as NMR studies (Miller et indicate that the proton is taken up by coordinated OH in the oxidized state to... 

A distorted tetrahedral environment of sulfur ligands was found for rubredoxin, which contains [IFe-OS] and is an intermediate electron carrier in the co-hydroxylation of fatty acids in Pseudomonas oleovorans. Fe cycles between the Fe(II) and Fe(Ill) states with E°= + 20 mV vs. NHE in the protein... 

Ambrosini E, Ferrante S, Schauer T, Ferrigno G, Molteni F, and Pedrocchi A, An automatic identification procedure to promote the use of FES-cycling training for hemiparetic patients. Journal of Healthcare Engineering, vol. 5 3, pp 275-292,2014. 

If pyrite and calcite form during diagenesis according to reaction (5.61), O2 generates. However decompositions of pyrite and calcite by weathering cause lower atmospheric O2 concentration. Above reaction implies that atmospheric O2 concentration depends not only on O2 cycle but also on S, Ca and Fe cycles. Sr incorporates into carbonate. Therefore, O2 concentration also depends on Sr cycle. 

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