Iron-sulfur clusters catalytic activity

Two [Fe] hydrogenase structures have so far been determined from C. pasteurianum (Cp) (Peters et al. 1998) and D. desulfuricans (Dd) (Nicolet et al. 1999). They have in common a large domain, which contains the catalytic site and three [4Fe-4S] iron sulfur clusters. The catalytic site and the closest (proximal) cluster are deeply buried inside the protein between two domains (or lobes), with access to a third, ferredoxin-like, domain that contains the two remaining (medial and distal) clusters. By contrast with [NiFe] hydrogenases the proximal [4Fe-4S] cluster is directly bridged to the bin-uclear active site by a cysteic thiolate (Fig. 6.12). 

Activation of an M-CO bond for nucleophilic substitution in anion radical metallo-complexes appears to be quite a general effect (Kaim 1987 Mao et al. 1989,1992 Shut et al. 1995 Klein et al. 1996). Such activation seems to be the basis of metal-cluster catalytic activity. The iron-sulfur cluster (Bu4N)2Fe4S4(SPh)4 deserves to be mentioned here. The cluster is considered as a ferredoxin model (Inoue Nagata 1986) it catalyzes an electron transfer from //-butyl lithium or phenyl lithium to 5-phenyl thiobenzoate or phenylbenzoate (Inoue Nagata 1986). 

Biological Iron-Sulfur Clusters with Catalytic Activity... 

The discovery of the different dinuclear or cuboidal-type biological iron-sulfur clusters is associated with their natural occurrence in two oxidation states. They can all function as one-electron transferring agents. This redox function has been well established in many studies over a period of almost five decades [1-5], However, electron transfer is generally not considered to be a catalytic activity. It is typically a stoichiometric transfer between two complex redox proteins. Mechanistically, it is probably best described as outer sphere or not involving the breaking and making of covalent bonds other than those related to hydrons. 

Aconitase was the first protein to be identified as containing a catalytic iron-sulfur cluster [24-26]. It was also readily established that the redox properties of the [4Fe-4S](2+ 1+) cluster do not play a role of significance in biological functioning the 1 + oxidation state has some 30% of the activity of the 2+ state [25], Since then several other enzymes have been identified or proposed to be nonredox iron-sulfur catalysts. They are listed in Table 2. It appears that all are involved in stereospecific hydration reactions. However, these proteins are considerably less well characterized than aconitase. In particular, no crystal structural information is available yet. Therefore, later we summarize structural and mechanistic information on aconitase, noting that many of the basic principles are expected to be relevant to the other enzymes of Table 2. 

Denke, E., Merbitz-Zahradnik, T., Hatzfeld, O. M., Snyder, C. H., Link, T. A., and Trumpower, B. L., 1998, Alteration of the midpoint potential and catalytic activity of the rieske iron-sulfur protein by changes of amino acids forming hydrogen bonds to the iron-sulfur cluster, J. Biol. Chem. 273 9085n9093. 

Iron sulfur clusters appear in a great many proteins as both electron-transport and enzymatic sites see Iron-Sulfur Proteins), for this reason there has been great interest for 30 years in the development and nnderstanding of iron-snlfur model complexes. Both stmctnre and properties of synthetic analogs of 1-, 2-, 3-, and 4-iron protein active sites have been stndied extensively. This article will address the stmctnral and chemical properties, synthesis, and catalytic activity of these synthetic analogs, as compared to the native protein-bound iron-sulfur cores. 

This volume begins with a discussion of iron sulfur clusters, a familiar topic to bioinorganic chemists and one that has not lost its appeal. Although long known for their role in biological electron transfer, they have recently been shown also to possess catalytic activity through subsite specific chemistry, wherein one of the iron atoms in the cube catalyzes chemical transformation at its particular corner. To reproduce such disymmetry in an... 

The presence of an Fe-S cluster in pi was soon obvious from the UV-visible spectrum which showed a broad band at 420nm and a shoulder at 330nm (Figure 10-2). Metal and sulfur analyses confirmed the presence of roughly equal amounts of iron and sulfide [42]. Lability of the iron explained why it was lost during purification and why pure recombinant pi protein contained substoichiometric amounts of iron, with the catalytic activity of the different preparations closely following their iron... 

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