Core extrusion

Core extrusion studies—removal of the iron-sulfur cluster intact from the enzyme surroundings—have been carried out and the iron-cluster types in proteins identified through the process shown in equation 6.10.18 DMS0/H20 is the protein unfolding solvent for this process. By this method, Fe-protein and MoFe-protein metal-sulfur clusters have been removed from the holoenzyme for separate analysis by many instrumental techniques. 

Some of the earlier approaches to the characterization of iron-sulfur clusters have proved to be inadequate in the presence of mixtures of clusters and, particularly, three-iron clusters. Thus the technique of core extrusion has worked well for [2Fe-2S] and [4Fe-4S] cores, but led to confusing results for aconitase and Fdl from A vinelandii as [2Fe-2S] cores were extruded. 

Since 1980, newer physical techniques such as Mdssbauer spectroscopy, X-ray absorption spectroscopy and iron-sulfur-core extrusion have been used to address the question of the structure of FeS-X. The initial Mossbauer spectroscopic study by (EH) Evans, Rush, Johnson and (MC W) Evans2o indicated... 

The most important reactions of synthetic Fe-S clusters are electron transfer and ligand substitution. The latter reaction forms the basis of the core extrusion method (66), useful for identifying certain clusters present in proteins, and allows the introduction of diverse chemical environments around the Fe-S cluster. We begin our consideration of subsite properties by summarizing the environments thus far achieved synthetically in [4Fe-4S] clusters. 

Iron-proteins can themselves participate in thiolate substitution reactions. There are indeed two types of this kind of process, namely active center core extrusion and protein reconstitution. Both are related to displacement of the Fe-S core between the protein and an appropriate organic thiol ... 

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