Iron-sulphur

Figure 8.39 shows some results of EXAFS following absorption by iron atoms in proteins with three prototype iron-sulphur active sites. In the example in Figure 8.39(a) application of a 0.9-3.5 A filter window before Fourier retransformation shows a single wave resulting... [Pg.331]

The presence of active sulphate-reducing bacteria usually results in graphitic corrosion and this has led to a useful method of diagnosing this cause of corrosion. The leaching out of iron from the graphitic residue which is responsible for the characteristic appearance of this type of corrosion leads to an enriched carbon, silicon and phosphorus content in the residue as compared with the original content of these elements in the cast iron. Sulphur is usually lost to some extent but when active sulphate-reducing bacteria are present, this loss is offset by the accumulation of ferrous sulphide in the residue with a consequent increase in the sulphur content of the residue out... [Pg.589]

In mitochondria (Fig. lb), the electron acceptor protein is also a flavoprotein termed NADPH-adrenodoxin reductase (MW 50 kDa) because it was discovered in the adrenal cortex and because it donates its electrons not directly to the P450 but to the smaller redox protein adrenodoxin (MW 12.5 kDa). The two iron-sulphur clusters of this protein serve as electron shuttle between the flavoprotein and the mitochondrial P450. [Pg.922]

Oxidation-reduction and substitution reactions of iron sulphur centres. F. Armstrong, Adv. Inorg. Bioinorg. Mech., 1982,1, 65-120 (167). [Pg.37]

Synthetic approaches to the active sites of iron-sulphur proteins. R. H. Holm, Acc. Chem. Res.,... [Pg.53]

Iron-sulphur proteins structural chemistry of their chromophores and related systems. R. Mason and J. A. Zubieta, Angew. Chem., Int. Ed. Engl., 1973,12, 390-399 (101). [Pg.55]

All the complexes consist of several subunits (Table 2) complex I has a flavin mononucleotide (FMN) prosthetic group and complex II a flavin adenine dinucleotide (FAD) prosthetic group. Complexes I, II, and III contain iron-sulphur (FeS) centers. These centers contain either two, three, or four Fe atoms linked to the sulphydryl groups of peptide cysteine residues and they also contain acid-labile sulphur atoms. Each center can accept or donate reversibly a single electron. [Pg.121]

Complex II contains four peptides, the two largest form succinate dehydrogenase, the largest has covalently boiuid flavin adenine dinucleotide (FAD) which reacts with succinate, and the other has three iron-sulphur centers. Smaller subunits anchor the two larger subunits to the membrane and form the UQ binding site. Ubiquinone is the electron acceptor but complex II does not pump protons (see below). [Pg.126]

The nuclear-encoded proteins are inserted into both inner and outer mitochondrial membranes, the intermembrane space, and the matrix and there are several different mechanisms involved. As mentioned above there is no apparent requirement for a presequence on proteins which insert specifically into the mitochondrial outer membrane. For proteins destined for the inner mitochondrial membrane, a stop-transfer mechanism is proposed. Thus some information in the peptide must stop the complete transfer of the protein into the mitochondrial matrix, enabling the protein to remain in the inner mitochondrial membrane. For some proteins in the intermembrane space (for example the Rieske iron-sulphur protein associated with the outer face of complex III), a particularly complicated import pathway... [Pg.140]

Moist diethyl sulphate was stored in an iron reservoir, which detonated after a little while. This accident was explained by the hydrolysis of the sulphate present that gives rise to the formation of sulphuric acid. By reacting with iron, sulphuric acid formed hydrogen that caused the overpressure responsible for the detonation. [Pg.348]

The feature of xanthine oxidase which is no doubt of the greatest chemical interest, is the presence of several non-protein components. Much effort has been expended in attempting to elucidate the respective roles of iron, flavin and molybdenum in the various enzyme catalysed reactions. Numerous studies of the iron constituent have been made of late (45, 46, 47, 48, 49, 50), it having been found to be of the iron-sulphur (51 a, 51 b) type. Neither iron (19) nor molybdenum (31) can be removed reversibly from the enzyme, though the FAD can be (52, see below). [Pg.115]

The role of the iron-sulphur system of xanthine oxidase in the catalytic reaction is somewhat problematical. Nevertheless, it is clear, both from rapid freezing EPR (53) and from stopped-flow measurements monitored optically at 450 nm (58, 63) (where both iron and flavin are measured), that iron is reduced and oxidized at catalytically significant rates. Perhaps the best interpretation is that it functions as a store for reducing equivalents within the enzyme when this is acting as an oxidase, though it may well represent the main site of electron egress in dehydrogenase reactions (52). [Pg.117]

A current overall picture of the reaction mechanism of xanthine oxidase, which differs substantially from one proposed earlier (87) is as follows. The enzyme is presumed to have two independent catalytic units, though this has not so far been proved rigorously. Reducing substrates are bound at molybdenum and reduce this from Mo(VI) both to Mo(V) and to Mo (IV). Reducing equivalents are then transferred by intramolecular reactions from molybdenum to iron-sulphur and also, either directly or via this, to flavin. Oxidizing substrates as a class, seem capable of reacting with all three types of centre in the enzyme. Thus, oxygen reacts predominantly with flavin, phenazine methosulphate... [Pg.138]

Cairns-Smith, as the leading proponent of the mineral theory, has also shown interest in both the hydrothermal biogenesis theory (Cairns-Smith, 1992) and the iron-sulphur hypothesis proposed by G. Wachtershauser (see Sect. 7.3). [Pg.184]

When the Fe2+/Fe3+ system is included, the thioester hypothesis, with its roots in sulphur chemistry, shows clear links with the iron-sulphur world of Wachtershauser s chemoautotrophic biogenesis model (see Sect. 7.3). [Pg.207]

Thermochemistry. Chen et al.168 combined the Kohn-Sham formalism with finite difference calculations of the reaction field potential. The effect of mobile ions into on the reaction field potential Poisson-Boltzman equation. The authors used the DFT(B88/P86)/SCRF method to study solvation energies, dipole moments of solvated molecules, and absolute pKa values for a variety of small organic molecules. The list of molecules studied with this approach was subsequently extended182. A simplified version, where the reaction field was calculated only at the end of the SCF cycle, was applied to study redox potentials of several iron-sulphur clusters181. [Pg.113]

Imlay, J.A. (2006) Iron-sulphur clusters and the problems with oxygen, Mol. Microbiol., 59, 1073-1082. [Pg.239]

Figure 15.6 The Wood-Ljungdahl pathway. One molecule of C02 (blue) is converted to formate and then reduced to a methyl group, which is then transferred to the corrinoid-iron-sulphur protein CFeSP. CFeSP transfers the methyl group to the A-cluster of the bifunctional CODH/ACS. The other molecule of C02 (red) is reduced to CO by the C-cluster of the CODH subunit. The CO is then transferred to the A-cluster through a long channel, some 70 A long, where with the methyl group and CoA it forms acetylCoA. (From Drennan et al., 2004. With kind permission of Springer Science and Business Media.)...

With an iron-sulphur protein as acceptor Acting on single donors with incorporation of molecular oxygen (oxygenases) 1.18 1.18.1 Acting on reduced ferredoxin as donor With NAD+ or NADP+ as acceptor... [Pg.475]

Johnson MK, Morningstar JE, Cecchini G, Ackrell BAC. 1985. Detection of a tetranuclear iron sulphur centre in fumarate reductase from Escherichia coli by EPR. Arch Microbiol 131 756-62. [Pg.125]

Fig. 1. Schematic representation of the four basic types of iron-sulphur clusters. The rubredoxin-type and the [2Fe-2S], [3Fe—4S] and [4Fe-4S] clusters are shown in (a) to (d), respectively. Reprint from Prog. Biophys. Mol. Biol., Vol. 70, H. Sticht and P. Rosch, The structure of iron-sulfur proteins , pp. 95-136, Copyright 1998, with permission from Elsevier Science.

As with some other enzymes involved in the generation of ATP in the mitochondria (e.g. oxoglutarate dehydrogenase), aconitase possesses an iron-sulphur complex in its... [Pg.349]

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