Iron-sulfur proteins functions

Pereira MM, Carita JN, Teixeira M. 1999. Membrane-bound electron transfer chain of the ther-mohalophilic bacterium Rhodothermus marinus Characterization of the iron- sulfur centers from the dehydrogenases and investigation of the high-potential iron- sulfur protein function by in vitro reconstitution of the respiratory chain. Biochemistry 38 1276. 

Capozzi F, Ciurli S, Luchinat C (1998) Coordination Sphere Versus Protein Environment as Determinants of Electronic and Functional Properties of Iron-Sulfur Proteins 90 127-160... 

A preliminaiy characterization of a new iron—sulfur protein isolated from Desulfovibrio vulgaris Hildenborough was reported in 1989 124). The protein contained approximately 6 iron and 6 inorganic sulfur atoms per molecule. The FPR spectrum of the dithionite reduced protein exhibited an S = signal similar to what was found for synthetic compounds with a [6Fe-6S] core (prismane core). No other FPR signals were reported at this time, and based on the observed similarity it was suggested that this peculiar iron-sulfur protein contained a [6Fe-6S] cluster. Because it had no known function, the pro-... 

APPLICATION OF EPR SPECTROSCOPY TO THE STRUCTURAL AND FUNCTIONAL STUDY OF IRON-SULFUR PROTEINS... 

The many redox reactions that take place within a cell make use of metalloproteins with a wide range of electron transfer potentials. To name just a few of their functions, these proteins play key roles in respiration, photosynthesis, and nitrogen fixation. Some of them simply shuttle electrons to or from enzymes that require electron transfer as part of their catalytic activity. In many other cases, a complex enzyme may incorporate its own electron transfer centers. There are three general categories of transition metal redox centers cytochromes, blue copper proteins, and iron-sulfur proteins. 

Although also iron-sulfur proteins, the rubredoxins do not generate H2S on acidification since in this case the thiol groups are contributed by cysteinyl residues in the polypeptide chain. The function of clostridial rubredoxin is as yet unknown in Pseudomonas sp. a similar protein catalyzes the co-hydroxylation of alkanes, a reaction requiring molecular O2. 

There is some evidence that the iron-sulfur protein, FhuF, participates in the mobilization of iron from hydroxamate siderophores in E. coli (Muller et ah, 1998 Hantke, K. unpublished observations). However, a reductase activity of FhuF has not been demonstrated. Many siderophore-iron reductases have been shown to be active in vitro and some have been purified. The characterization of these reductases has revealed them to be flavin reductases which obtain the electrons for flavin reduction from NAD(P)H, and whose main functions are in areas other than reduction of ferric iron (e.g. flavin reductase Fre, sulfite reductase). To date, no specialized siderophore-iron reductases have been identified. It has been suggested that the reduced flavins from flavin oxidoreductases are the electron donors for ferric iron reduction (Fontecave et ah, 1994). Recently it has been shown, after a fruitless search for a reducing enzyme, that reduction of Co3+ in cobalamin is achieved by reduced flavin. Also in this case it was suggested that cobalamins and corrinoids are reduced in vivo by flavins which may be generated by the flavin... 

The reaction-center proteins for Photosystems I and II are labeled I and II, respectively. Key Z, the watersplitting enzyme which contains Mn P680 and Qu the primary donor and acceptor species in the reaction-center protein of Photosystem II Qi and Qt, probably plastoquinone molecules PQ, 6-8 plastoquinone molecules that mediate electron and proton transfer across the membrane from outside to inside Fe-S (an iron-sulfur protein), cytochrome f, and PC (plastocyanin), electron carrier proteins between Photosystems II and I P700 and Au the primary donor and acceptor species of the Photosystem I reaction-center protein At, Fe-S a and FeSB, membrane-bound secondary acceptors which are probably Fe-S centers Fd, soluble ferredoxin Fe-S protein and fp, is the flavoprotein that functions as the enzyme that carries out the reduction of NADP+ to NADPH. 

Application of EPR Spectroscopy to the Structural and Functional Study of Iron-Sulfur Proteins Bruno Guigliarelli and Patrick Bertrand... 

Most mechanisms which control biological functions, such as cell respiration and photosynthesis (already discussed in Chapter 5, Section 3.1), are based on redox processes. In particular, as shown again in Figure 1, it is evident that, based on their physiological redox potentials, in photosynthesis a chain of electron carriers (e.g. iron-sulfur proteins, cytochromes and blue copper proteins) provides a means of electron transport which is triggered by the absorption of light. 

Kaut A, Lange H, Diekert K, et al. 2000. Isalp is a component of the mitochondrial machinery for maturation of cellular iron-sulfur proteins and reqnires conserved cysteine residues for function. J Biol Chem 275 15955-61. 

A class of iron-sulfur proteins lacking acid-labile sulfur, but similar in function to the ferredoxins. The iron center is coordinated by four sulfur-containing hgands, usually from cysteinyl residues. Where known, these proteins function as electron carriers. 

The recent progress in the area of biological functions and molecular properties of iron-sulfur proteins has been phenomenal, and comprehensive summaries of these proteins have appeared in many reviews (2,3,4,5) and books (6,7,8). In this paper, the properties of some of the well understood iron-sulfur proteins will be briefly described. An effort will be made then to relate these properties to their possible participation in degradation reactions on organic chemicals, and particularly on pesticide chemicals. 

Adrenodoxin. Adrenodoxin is the only iron-sulfur protein which has been isolated from mammals. This protein from mitochondria of bovine adrenal cortex was purified almost simultaneously by Kimura and Suzuki (32) and Omura et al. (33). It has a molecular weight of 12,638 (34) and the oxidized form of the protein shows maximal absorbances at 415 and 453 nm. Adrenodoxin acts as an electron carrier protein in the enzyme system required for steroid hydroxylation in adrenal mitochondria. In this system, electron transfer is involved with three proteins cytochrome P. gQ, adrenodoxin and a flavoprotein. Reduced NADP gives an electron to Tne flavoprotein which passes the electron to adrenodoxin. Finally, reduced adrenodoxin transfers the electron to cytochrome Pas shown in Fig. 3. The mechanism of cytochrome P cq interaction with steroid, oxygen and adrenodoxin in mixed-function oxidase of adrenal cortex mitochondria has been reviewed by Estabrook et al. (35). 

Putidaredoxin. Cushman et al. (36) isolated a low molecular iron-sulfur protein from camphor-grown Pseudomonas putida. This protein, putidaredoxin, is similar to the plant type ferredoxins with two irons attached to two acid-labile sulfur atoms (37). It has a molecular weight of 12,000 and shows absorption maxima at 327, 425 and 455 nm. Putidaredoxin functions as an electron transfer component of a methylene hydroxylase system involved in camphor hydroxylation by P. putida. This enzyme system consists of putidaredoxin, flavoprotein and cytochrome P.cQ (38). The electron transport from flavoprotein to cytochrome P.cq is Smilar to that of the mammalian mixed-function oxidase, but requires NADH as a primary electron donor as shown in Fig. 4. In this bacterial mixed-function oxidase system, reduced putidaredoxin donates an electron to substrate-bound cytochrome P. g, and the reduced cytochrome P. g binds to molecular oxygen. One oxygen atom is then used for substrate oxidation, and the other one is reduced to water (39, 40). 

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