Ferredoxin

Ferredoxins (from Latin ferrum: iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. They contain iron and sulfur atoms organized as iron–sulfur clusters. These biomolecules accept or discharge electrons, with the effect of a change in the oxidation state of the iron atoms between +2 and +3, letting them act as electron transfer agents in biological redox reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic bacterium Clostridium pasteurianum. Other bioinorganic electron transport systems include rubredoxins, cytochromes, blue copper proteins, and the structurally related Rieske proteins. Another redox protein, isolated from spinach chloroplasts, was termed "chloroplast ferredoxin". The chloroplast ferredoxin is involved in both cyclic and non-cyclic photophosphorylation reactions of photosynthesis. In non-cyclic photophosphorylation, ferredoxin is the last electron acceptor thus reducing the enzyme NADP + reductase. It accepts electrons produced from sunlight-excited chlorophyll and transfers them to the enzyme ferredoxin: NADP + oxidoreductase . Ferredoxins can be classified according to the nature of their iron–sulfur clusters and by sequence similarity.

Ferredoxins (from Latin ferrum: iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. They contain iron and sulfur atoms organized as iron–sulfur clusters. These biomolecules accept or discharge electrons, with the effect of a change in the oxidation state of the iron atoms between +2 and +3, letting them act as electron transfer agents in biological redox reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic bacterium Clostridium pasteurianum. Other bioinorganic electron transport systems include rubredoxins, cytochromes, blue copper proteins, and the structurally related Rieske proteins. Another redox protein, isolated from spinach chloroplasts, was termed "chloroplast ferredoxin". The chloroplast ferredoxin is involved in both cyclic and non-cyclic photophosphorylation reactions of photosynthesis. In non-cyclic photophosphorylation, ferredoxin is the last electron acceptor thus reducing the enzyme NADP + reductase. It accepts electrons produced from sunlight-excited chlorophyll and transfers them to the enzyme ferredoxin: NADP + oxidoreductase . Ferredoxins can be classified according to the nature of their iron–sulfur clusters and by sequence similarity. Ferredoxins are one of the most reducing biological electron carriers. They typically have a mid point potential of -420 mV. The reduction potential of a substance in the cell will differ from its midpoint potential depending on the concentrations of its reduced and oxidized forms. For a one electron reaction, the potential changes by around 60 mV for each power of ten change in the ratio of the concentration. For example, if the ferredoxin pool is around 95% reduced, the reduction potential will be around -500 mV. In comparison, other biological reactions mostly have less reducing potentials. For example, the primary biosynthetic reductant of the cell, NADPH, has a cellular redox potential of -370 mV ( = -320 mV). Depending on the sequence of the supporting protein, ferredoxins have reduction potential from around -500 mV to -340 mV. Organisms typically host multiple types of ferredoxins. + + + + + + + +

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