Oxford Instruments Cryomagnet Spectromag 4000 acquired in 2007
Iron-sulfur clusters (ISC) were present in the most ancient organisms and have adapted to aerobic life. They constitute one of the most widespread and important class of proteins, being involved in numerous essential biological processes: electron transfer in respiratory chain, iron and superoxide sensing, and a large panel of enzymatic functions such as hydrolysis of substrates, bond formations (DNA synthesis, RNA modification, biotin synthesis, ...) to mention only a few
[7-8]. They are constituted by assemblies of iron and sulfide ions anchored to protein cysteinate residues
. Although various nuclearities have been found, the [2Fe-2S] and [4Fe-4S] clusters are the most commonly encountered. They can exist in several oxidation states but again the [2Fe-2S]+/2+ and [4Fe-4S]+/2+ are the most common. In a simple (maybe simplistic) view the [2Fe-2S]+ cluster can be described as a pair of strongly antiferromagnetically coupled Fe2+–Fe3+ ions bridged by two sulfide S2– ions, that possesses an overall spin S = 1/2 and is EPR active. Its oxidized form [2Fe-2S]2+ involves a strongly antiferromagnetically coupled pair of ferric ions Fe3+–Fe3+ with a resulting overall spin S = 0. It is EPR silent as the cluster [4Fe-4S]2+. Indeed in the latter, the four iron ions assembly can be viewed as an antiferromagnetically coupled dimer of the above Fe2+–Fe3+ pairs, thus leading to an overall spin S = 0. One-electron reduction to the [4Fe-4S]+ state that is composed of one ferric and three ferrous ions restores an overall spin S = 1/2 and the associated EPR spectrum. As a consequence of these diverse electronic states, every one of these clusters exhibits a distinct Mössbauer signature that is used to identify protein active sites and to monitor their functional changes
Biogenesis of iron-sulfur proteins and dysfunction
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