Proteins ferredoxins

Redox Fe-S proteins High-potential iron protein Ferredoxin Viral coat proteins f Tomato bushy stunt virus protein I Southern bean mosaic virus protein Tobacco mosaic virus protein... 

Mossbauer studies of the electron transport protein ferredoxin n from Desulfovibrio gigas have shown that the reduced Fe3S4 cluster contains one trapped valence Fe3+ site and one delocalized Fe2+-Fe3+ pair. The two Fe of the delocalized pair are indistinguishable, and the pair has a dimer spin S12 = 9/2, suggesting ferromagnetic coupling. 

Polynuclear Fe-M-S Complexes from "spontaneous self assembly" reactions. Synthetic analog clusters for the Fe2S2 and Fe4S4 centers in the Fe/S proteins (ferredoxins) have been obtained by procedures that are based on the concept of "spontaneous self assembly". The latter (30) assumes that the cores of the Fe/S centers are thermodynamically stable units that should be accessible fiom appropriate reagents even in the absence of a protein environment. 

Ferredoxins, iron-sulfur proteins ferredoxin + le —> ferrodoxin,ed -0.36... 

The multinuclear tetrahedral iron clusters have the potential for additional formal oxidation states. Because not all of these states have been found in proteins or model compounds, it is possible that some oxidation states may be unstable. For a given Fe S protein only one redox couple is used the other possible states appear to be excluded by restrictions of the protein structure. This selection rule is illustrated with two 4Fe 4S low-molecular-weight electron transfer proteins ferredoxin and high-potential iron protein (HiPIP). The 4Fe 4S clusters in both proteins were shown by X-ray crystallography to be virtually identical. However, the redox potential and oxidation states for the two proteins are vastly... 

However, in contrast to the cyclic flow of electrons in purple bacteria, some electrons flow from the reaction center to an iron-sulfur protein, ferredoxin, which then passes electrons via ferredoxin NAD reductase to NAD+, producing NADH. The electrons taken from the reaction center to reduce NAD+ are replaced by the oxidation of H2S to elemental S, then to SOf, in the reaction that defines the green sulfur bacteria. This oxidation of H2S by bacteria is chemically analogous to the oxidation of H20 by oxygenic plants. 

Figure 1. The Nitrogenase Reaction. The electron transfer proteins ferredoxin (Fd) and flavodoxin (Fid) serve to couple the nitrogenase reaction to metabolically generated reducing equivalents. Ammonia synthesis requires 8 electrons 6 for the reduction of dinitrogen and 2 for the coupled, obligatory synthesis of H2. These reactions are catalyzed by the terminal component in the complex, the MoFe-protein. The electrons are transferred to the MoFe-protein from the Fe-protein in a process coupled to the hydrolysis of 2ATP/electron (Howard and Rees, 1994,1996).

Fe Fe2+, Fe3+ 1-2 mg Proline hydroxylase, diphosphoribonucleo-side dehydrogenase, peroxidases Component of hemoglobin and all other heme proteins component of iron-sulfur proteins (ferredoxins)... 

Monooxygenase reactions catalyze the introduction of only one of the two oxygen atoms from molecular oxygen to form a hydroxyl or keto group in the substrate. The other oxygen atom ends up in water. Both the substrate and the NADPH act as proton and electron donors. Monooxygenase reactions occur in the ER membrane and involve iron-sulfur proteins, ferredoxin, and cytochrome P450-... 

The electron from P reduces the iron-containing protein, ferredoxin (Table 5-3), through a series of five intermediates. Electron transfer to the first component, which is a Chi a, is rapid (about 2 x 10-12 s) the next... 

Three bound Fe-S centres have been proposed to be the next acceptors (see Refs. 29, 48 and 49 for reviews), on the basis of optical and EPR spectroscopy and Mdssbauer studies. The stable, one-electron acceptor of PS I is a soluble Fe-S protein, ferredoxin (Fd) [50], of molecular weight of 10 kDa and = -440 mV. So, PS I transfers electrons against an apparent electrochemical gradient of ca. 0.9 V. 

Brought to the stroma side by the succession of photosystems, one now finds a number of electrons carried by the proteins ferredoxin and flavo-doxin. Furthermore, protons (positively charged hydrogen ions) have been separated and moved across the thylakoid membrane (thereby creating an gradient from lumen to stroma). This makes room for two types of recombination processes on the stroma side. One is the "normal" reaction in plants and most bacteria ... 

Redox-active proteins ferredoxin, cytochromes, and others... 

Redox proteins are relatively small molecules. In biological systems they are membrane associated, mobile (soluble) or associated with other proteins. Their molecular structure ensures specific interactions with other proteins or enzymes. In a simplified way this situation is mimicked when electrodes are chemically modified to substitute one of the reaction partners of biological redox pairs. The major classes of soluble redox active proteins are heme proteins, ferredoxins, flavoproteins and copper proteins (Table 2.1). In most cases they do not catalyze specific chemical reactions themselves, but function as biological (natural) electron carriers to or between enzymes catalyzing specific transformations. Also some proteins which are naturally not involved in redox processes but carry redox active sites (e.g., hemoglobin and myoglobin) show reversible electron exchange at proper functionalized electrodes. 

The membrane-bound iron-sulfiir centers were discovered by Dick Malkin and Alan Bearden in 1971 in spinach chloroplasts using EPR spectroscopy. Since the EPR spectrum was found to resemble that of the iron-sulfur protein ferredoxin and since the soluble ferredoxin had already been removed from the chloroplast sample used in the measurement, the substance represented by the newly found EPR spectrum was initially called membrane-bound ferredoxin. And since the iron-sulfur center was also found to be photo-reducible at cryogenic temperature, it was therefore suggested that it was the primary electron acceptor of photosystem I. 

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