Clostridial ferredoxin isolation

Monomeric ferredoxins have been isolated and characterized from three methano-sarcinaceae [124-127] and one methanococcal species [128,129]. The methanosarcinal ferredoxins have primary sequences similar to clostridial 2x[4Fe-4S] ferredoxins but differ in the configuration of their [Fe-S] centers. Although the ferredoxins isolated from M. barkeri MS and M. barkeri Fusaro both have molecular masses of approximately 6 kDa they contain a [3Fe-3S] cluster and 2x[4Fe—4S] clusters, respectively. The ferredoxin from Methanosarcina thermophila has a molecular mass of only 4.9 kDa and contains either a [3Fe-3S] or a [4Fe-4S] center. These ferredoxins appear to be involved in electron transport from pyruvate dehydrogenase and from CODH [125,130]. A ferredoxin purified from Methanococcus thermolithotrophicus has 2x[4Fe—4S] centers, a molecular mass of 7.3 kDa and also appears to accept electrons from CODH [128,129]. 

The name ferredoxin was first proposed for a non haem iron-redox-protein (hence its name) isolated from Clostridium pasteurianum and presumably involved in the hydrogen gas evolution from pyruvate by this bacterium (254). The smallest of the known iron-sulfur proteins, 6,000 dalton, the clostridial ferredoxins are, however, the most complex in terms of the iron and inorganic sulfur content 8Fe 8S. They are single chain polypeptides of about 55 residues of which eight are cysteines (Fig. 18). 

The isolation of the clostridial ferredoxin is remarkably simple (Table III). This is a very elegant isolation devised by Mortenson (48) and based on the fact that the protein is very small and soluble in acetone, whereas most soluble proteins will be precipitated. It is an extremely... 

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