Iron-sulfur proteins ligand

Iron Inorganic Coordination Chemistry Iron Proteins for Storage Transport their Synthetic Analogs Iron-Sulfur Proteins Ligand Field Theory Spectra Metal Ion Toxicity Metalloregulation. 

In this review we will deal with iron-sulfur proteins where the iron atoms are coordinated only by cysteine ligands and bridging sulfurs, as well as rubredoxin (Rd hereafter), which is the initial building block in all subsequent discussions. 

Formate dehydrogenases are a diverse group of enzymes found in both prokaryotes and eukaryotes, capable of converting formate to CO2. Formate dehydrogenases from anaerobic microorganisms are, in most cases, Mo- or W- containing iron-sulfur proteins and additionally flavin or hemes. Selenium cysteine is a Mo- ligand. 

Iron-sulfur proteins. In an iroinsulfiir protein, the metal center is surrounded by a group of sulfur donor atoms in a tetrahedral environment. Box 14-2 describes the roles that iron-sulfur proteins play in nitrogenase, and Figure 20-30 shows the structures about the metal in three different types of iron-sulfur redox centers. One type (Figure 20-30a l contains a single iron atom bound to four cysteine ligands. The electron transfer reactions at these centers... 

The remarkable range of redox potentials in the iron sulfur proteins, already noted, illustrates the principle that nature, having discovered a ligand system, attempts to extract from it the maximum utility. Certainly the outstanding problem awaiting solution in these proteins is an explanation for the relationship between structure and redox potential. Thus... 

There are two types of electron transport those involving flavoproteins and iron-sulfur proteins, and those requiring only flavoproteins. The X-ray crystal structure of the soluble cytochrome P450 from Pseudomonas putida grown on camphor (P-450-CAM) has been determined (Poulos et ah, 1985), as have several others. The haem group is deeply embedded in the hydrophobic interior of the protein, and the identity of the proximal haem iron ligand, based on earlier spectroscopic studies (Mason et ah, 1965) is confirmed as a specific cysteine residue. 

The state of knowledge on iron-sulfur proteins which contain non-heme iron bonded to sulfur ligands (cysteinyl residues from the protein and inorganic sulfur) has been reviewed by several authors258"264. With magnetic resonance techniques it has been possible to obtain detailed information on the nature of the active site in many of these proteins. The contributions from ENDOR have recently been summarized by Sands265 so that we shall only give an outline of the crucial points. 

Fe-S proteins contain four basic core structures, which have been characterized crystal-lographically both in model compounds (Rao and Holm, 2004) and in iron-sulfur proteins. These are (Figure 3.6), respectively, (A) rubredoxins found only in bacteria, in which the [Fe-S] cluster consists of a single Fe atom liganded to four Cys residues—the iron atom... 

A structural unit within iron-sulfur proteins, comprising two or more iron atoms and bridging sulfur atoms (also termed sulfide ligands or sulfido-bridges). These bridging sulfur atoms are acid-labile, generating H2S in the pres-... 

A mitochondrial respiratory chain iron-sulfur protein containing a [2Fe-2S] cluster with two coordinated cys-teinyl sulfur ligands and two coordinated histidyl imidazole ligands. The term is also apphed to similar proteins isolated from photosynthetic organisms and microorganisms that contain similarly coordinated [2Fe-2S] clusters. 

The prosthetic groups of iron-sulfur proteins fall into several classes (Lov-enberg, 1977 Spiro 1982). Rubredoxins bind single iron atoms with four cys-teinyl sulfur ligands they function as electron carriers in some bacterial systems. Rubredoxins generally have two such centers per molecule in the ferric state each iron center is EPR detectable. 

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