Ferredoxins Subject

The second class of iron-containing proteins which have been well-studied by Mossbauer spectroscopy, and by other resonance techniques, are the iron-sulfur proteins. These molecules are also known by the name, ferredoxins. Iron-sulfur proteins in several varieties serve as electron-transport agents for processes in plants, bacteria, and mammals. Perhaps the most-studied physiological process involving the iron-sulfur proteins is the study of their role in photosynthesis. This subject has been extensively reviewed by Arnon 126,135), Hind and Olson 127), Hall and... 

Although electron transfer as such is not considered as catalysis, most enzymatic redox reactions require the presence of electron-transfer proteins for fast and efficiently directed electron transfer to the active sites. The ferredoxins, azurins, and cytochromes are most well known in this respect. Variations of over 15 A in distance may occur, and as a consequence, the electron-transfer rate may vary over 10 orders of magnitude [35], Exciting developments are ongoing in this field, and are highly relevant for the bioinorganic catalytic subject. 

The past four years have witnessed major changes in concepts of anaerobic fermentative metabolism and photosynthesis, due mainly to recognition of the key role of ferredoxin. Ferredoxin is a non-heme iron protein, containing no flavin, which carries the most energetic electrons in metabolism. The cellular function and chemistry of ferredoxin are described in this chapter. This is not intended to be an all-inclusive review of the literature pertaining to ferredoxin. Certain aspects of the subject are discussed in the earlier articles of Mortenson (71), Valentine (106), and... 

Malstrom and Neilands (68). The recent reviews of San Pietro and Black (86) and Arnon (6) are more specifically concerned with ferredoxin in photosynthesis. Also pertinent to the general subject of ferredoxin are the symposia on photosynthesis in higher plants (Photosynthetic Mechanisms of Green Plants (82)) and on the role of non-heme iron proteins in energy conversion (San Pietro (55)). 

Another mechanism of light-dependent enzyme activation has been proposed in which a membrane-bound dithiol-containing factor (light-effect mediator or LEM) reduced by the photosynthetic electron transport system reductively activates regulated enzymes in the chloroplast [28]. Certain facets of this mechanism may be identical to the ferredoxin/thioredoxin system while other aspects are still the subject of debate [18,33],... 

The LEFE also indicated that Cp2 contained a 4Fe4S cluster. This effect measures the shift in g values of an epr center when subjected to a strong electric field. A shift will occur only if the charge distribution around the center is nonsymmetrical as in four-iron clusters (Peisach et al., 1977). The LEFE with Cp2 was equivalent to that of 4Fe4S ferredoxins and nearly ten times greater than that of 2Fe2S ferredoxins (Orme-Johnson et al., 1977). 

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