Iron-Sulfur Flavoproteins

Hans and co-workers showed that enzymes isolated from Acidaminococcus fermentans consists of a homodimeric component A (72, 2 x 11 kDa) and a heterodimeric component D (a, 50 kDa P, 45 kDa). Each component contains one [4Fe-4S] cluster, and component D contains one molecule of FMN and varying amounts ( 0.1) of riboflavin. The components were characterized by combination of Mossbauer, optical and EPR spectroscopy. The oxygen-sensitive 

Hans and co-workers also examined the enzyme from the related organism Clostridium symbiosum. Here, the heterodimer component D (a, 54 kDa P, 42 kDa) contains two [4Fe-4S] clusters, one molecule of FMN and varying amounts ( 0.2) of riboflavin. Mdssbauer spectroscopy revealed the symmetric cube-type structures of the two [4Fe-4S] clusters, while EPR showed that the clusters were resistant to reduction. A narrow signal atg = 2.004 was assigned to a rather stable flavin radical. The authors concluded that the substoichiometric amount of riboflavin found to date in all 2-hydroxyacyl-CoA dehydratases appears to be unnecessary for activity but nevertheless represents a characteristic feature of this class of enzymes. 

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Lim, L.W., et al. Three-dimensional structure of the iron-sulfur flavoprotein trimethylamine dehydrogenase at 2.4 A resolution. J. Biol. Chem. 261 15140-15146, 1986. 

An iron sulfur-flavoprotein that transfers electrons directly to the dioxygenase, as in phthalate dioxygenase (class I)... 

I, 2-diol and NAD. This multiprotein complex contains an iron-sulfur flavoprotein, an iron-sulfur oxygenase, and ferredoxin. See also Phthalate Dioxygenase... 

Benzoate 1,2-dioxygenase [EC 1.14.12.10], also called benzoate hydroxylase, catalyzes the reaction of benzoate with dioxygen and NADH to generate catechol, carbon dioxide, and NAD+. This is a multiprotein system which contains a reductase which is an iron-sulfur flavoprotein (FAD) and an iron-sulfur oxygenase. 

Glutamate synthase (NADPH) [EC 1.4.1.13], an iron-sulfur flavoprotein, catalyzes the reaction of L-glutamine with a-ketoglutarate (or, 2-oxoglutarate) and NADPH to produce NADP+ and two glutamate molecules. Ammonia can act as the nitrogen donor substrate instead of L-glutamine, albeit weaker. 

It should be noted that non-heme oxygenases can also degrade aromatics such as biphenyls and naphthalene (Scheme 7.23). A naphthalene dioxygenase consists of a catalytic oxygenase component with a mononuclear iron site, an iron-sulfur flavoprotein reductase and an iron-sulfur ferredoxin transferring electrons from... 

Massey, V. Iron-sulfur flavoprotein hydroxylases. In The iron-sulfur proteins (Lovenberg, W. ed.) Vol. 1, pp. 301-360, New York, Academic Press 1973... 

The CO dehydrogenase of the carboxidotrophic bacterium Oligotropha carboxidovorans is a molybdenum-containing iron-sulfur flavoprotein that catalyzes the oxidation of CO to CO2, generating a proton gradient across the cytoplasmic membrane (19, 20). 

X A new flavoprotein, containing iron and labile sulfide, has been discovered in the mitochondrial inner membrane independently by Ruzicka and Beinert (4SS) and Hatefi et al. (436). The protein contains acid-extractable FAD, and 4 g-atoms of iron and 4 moles of labile sulfide per mole of flavin. The molecular properties and the enzymic function of this iron-sulfur flavoprotein are not clear. 

A distinct electron transfer flavoprotein (ETF) is the single-electron acceptor for a variety of flavoprotein dehydrogenases, including acyl CoA, glutaryl CoA, sarcosine, and dimethylglycine dehydrogenases. It then transfers the electrons to ETF-ubiquinone reductase, the iron-sulfur flavoprotein that reduces ubiquinone in the mitochondrial electron transport chain. 

Trimethylamine dehydrogenase is an iron-sulfur flavoprotein found in the methylotrophic bacterium Methylophilus methylotrophus W3A1. It catalyzes the oxidative N-demethylation of trimethylamine by water with formation of dimethylamine and formaldehyde (Steenkamp and Mallinson, 1976). The protein is a symmetrical dimer consisting of 166kDa subunits (Kasprzak et al., 1983 Lim et al., 1982). Each subunit contains one 4Fe-4S center and one FMN cofactor. The latter is bound covalently through the 6... 

Gassner, G. T., Ludwig, M. L., Gatti, D. L., Correll, C. C., and Ballou, D. P., 1995, Stracture and mechanism of the iron-sulfur flavoprotein phthalate dioxygenase reductase. FASEB J. 9 1411nl418. 

Lim, L. W., Mathews, F. S., and Steenkamp, D. J., 1982, Crystallographic study of the iron-sulfur flavoprotein trimethylamine dehydrogenase from the bacterium W3A1. J. Mol. Biol. 162 8699876. 

Dobbek, H., Gremer, L., Meyer, O., and Huber, R., 1999, Crystal structure and mechanism of CO dehydrogenase, a molybdo iron-sulfur flavoprotein containing S-selanylcysteine, Proc. Nad. Acad. Sci. (USA) 96 8884118889. 

Heering, H.A., Weiner, J.H., and Armstrong, F.A. (1997) Direct detection and measurement of electron relays in a multicentered enzyme voltammetry of electrode-surface films of E. coli fumarate reductase, an iron-sulfur flavoprotein. Journal of the American Chemical Society, 119,11628-11638. 

In anaerobic archaea, ferredoxin functions as an intermediate electron acceptor of a variety of key steps in the central metabolic pathways involved in saccharolytic and peptide fermentation, and reduced ferredoxin thus formed donates its reducing equivalent to ferredoxiniNADP" oxidoreductase and hydrogenase. - In aerobic and thermoacidophilic archaea, the reoxidation steps of reduced zinc-containing ferredoxin are poorly characterized. The soluble fraction of Sulfolobus sp. strain 7 also contains an NADPH ferredoxin oxidoreductase activity, but this enzyme has not been purified and characterized. The following section describes the purification and partial characterization of a red iron-sulfur flavoprotein with a weak ferredoxin-reoxidizing activity fi om Sulfolobus sp. strain 7. ... 

Purification of Red Iron-Sulfur Flavoprotein. The red iron-sulfur flavoproteinis eluted from the DEAE-Sephacel column shortly after (or sometimes together with) the cognate 2-oxoacid ferredoxin oxidoreductase activity, as described above. The red-colored fractions are combined and made to 1 A/ ammonium sulfate solution by addition of solid ammonium sulfate at 4°, with stirring. 

Miscellaneous Iron-Sulfur Flavoproteins. 5.5.1 Alkene monooxygenase. Nocardia corallina B-276 possesses a multi-component enzyme, alkene monooxygenase, that catalyses the stereoselective epoxygenation of alkenes to give predominantly the R enantiomer. 

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