I have been thinking about some alternative CO₂ fixation pathways. As almost all of them include ferredoxin reduction I started to wonder where does the ferredoxin comes from. I could not find any of the pathway in databases (ecocyc,kegg). Does any of you know if the biochemical pathway and the genes involved in synthesis are known?


  • $\begingroup$ Wikipedia:"ferredoxin". Ferredoxins are proteins containing FeS centres. $\endgroup$ – Alan Boyd Feb 25 '14 at 18:19
  • $\begingroup$ Yes, that is the definition of them. But in which biochemical pathway are they produced... $\endgroup$ – MartinK Feb 25 '14 at 18:21
  • $\begingroup$ They are proteins: encoded by genes, synthesised by ribosomes. $\endgroup$ – Alan Boyd Feb 25 '14 at 18:49
  • $\begingroup$ I do understand that! But I am interested with which genes are they encoded! $\endgroup$ – MartinK Feb 25 '14 at 19:01
  • $\begingroup$ plantphysiol.org/content/134/1/255.full is a link to the full text of a paper about the ferredoxins of Arabidopsis. That should get you started: if you are interested in ferredoxins from some other species you could obtain the sequences of the A. thaliana proteins and use those to search in other genomes. $\endgroup$ – Alan Boyd Feb 25 '14 at 19:13

Ferredoxins and variants such as fladidoxins and rubredoxins are simply electron carrying protein that need to be regenerated, like the more energetic NADPH.
The key thing to remember is that redox balance is key. You cannot have electron pair accumulate so there has to be a terminal acceptor. In the case of aerobic resipration it is oxygen, in the case of iron or sulfur dissimilation it is iron(III) or sulfate, in the case of fermentation it is a small highly oxidised carbon (e.g. methanol, ethanol, butanediol, formate, acetate, propionate, lactate, succinate, fumarate). Carbon fixation requires electron pairs, which come from somewhere. The mechanism of how the carbon dioxide is assimilated can be via the Calvin cycle (plants and cyanobacteria), the Wood-Ljungdahl pathway or from the 3-hydroxypropionic cycle Prof. Fuchs described in Chloroflexi and Sulfolobus. In all three electrons come from somewhere (generally water, carbon monoxide and sulfur respectively).
The reason why there are both ferredoxins and NADPH is a tad harder to explain, but has to do with redox control and the fact that not always ferredoxin is regenerated by a NADPH reductase (also: NADH = catabolic, NADPH anabolic), but could be a fumarate reductase or similar.

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  • $\begingroup$ Thanks for your answer - Could you add resources and references? $\endgroup$ – AliceD Jun 6 '16 at 18:44

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