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Investigates the functions of iron-sulfur cluster regulator (IscR) on the expression of Escherichia coli (E. coli) genes. Role of transcription reactions for IscR in repression of the IscR promoter; Importance of Fe-S cluster for IscR function; Purification of IscR from E. coli B strain.

Examines the involvement of Jac1, a mitochondrial J-type chaperone, in the biogenesis of Fe/S clusters in Saccharomyces cerevisiae. Jac1 of the mitochondrial matrix; Importance of the J domain of Jac1 for its function; Genetic interactions among JAC1, SSQ1, NFU1 and ISU genes; Defective JAC1 mutant cells in Fe/S enzyme activities.

Presents an overview of the rapidly developing field of sulfur biochemistry. Role of sulfur in biological systems; Occurrence of sulfur in inorganic systems; Iron-sulfur cluster synthesis and disassembly; Iron-sulfur clusters as participants in reactions; Role of the sulfane carrying IscS protein in organic systems.

This review traces the history of understanding of the CuA site in cytochrome c oxidase (COX) form the beginnings, when few believed that there was any significant Cu in COX, to the verification of three atoms Cu/monomer and to the final identification of the site as a dinuclear, Cys-bridged average valence Cu1.5+... Cu1.5+ structure through spectroscopy, recombinant DNA techniques, and crystallography. The critical steps forward in understanding the nature of the CuA site are recounted and the present state (as of the end of 1996) of our knowledge of the molecular and electronic structure is discussed in some detail. The contributions made through the years by the development of methodology and concepts for solving the enigma of CuA are emphasized and impediments, often rooted in contemporary preconceptions and attitudes rather than solid data, are mentioned, which discouraged the exploitation of early valuable clues. Finally, analogies in construction principles of polynuclear Cu-S and Fe-S proteins are pointed out. [ABSTRACT FROM AUTHOR]

The sulfur-reducing bacterium Spirillum 5175 was investigated with regard to membrane constituents that might be part of the sulfur oxidoreductase which converts elemental sulfur to hydrogen sulfide. Regardless of the electron acceptor used for cultivation of the bacteria, i.e. elemental sulfur, fumarate, or nitrate (Sp. 5175S,F,N). the qualitative pattern of cytochromes and Fe-S proteins did not change significantly, as documented by ultraviolet/ visible and electron paramagnetic resonance spectroscopy of oxidized (as isolated) and reduced (dithionite) samples. With elemental sulfur the prominent cytochrome exhibited absorption maxima at 553, 522.5 and 426 nm in the reduced state. In fumarate-grown cells two prominent cytochromes were found with maxima at 561, 551, 530, 521 and 430 nm. Two b-type cytochromes with Em at –198 mV and —20 mV vs the standard hydrogen electrode were identified in the membrane fraction of Sp. 5175F. A yellow pigment was extracted and identified as a flexirubin-type pigment. Although present in large quantities, it seemed not to be involved in the reduction of elemental sulfur. Menaquinone, MK 6 (Mr 580) was the prominent quinone identified in Sp. 5175. Characterization of a second quinone was not attempted because of its much lower concentration. The membrane constituents of Sp. 5175 were solubilized by a variety of detergents and detergent mixtures. A colorimetric procedure with photochemically reduced phenosafranin as the electron donor and cysteamine trisulfide (RS-S-SR, R = —CH2CH2NH2) as the electron acceptor was used to detect sulfur oxidoreductase activity. Three membrane proteins of Sp. 5175 were purified: (1) an [NiFe] hydrogenase, homogeneous by SDS/ polyacrylamide gel electrophoresis, with electron paramagnetic resonance signals as isolated at gx,y,z = 2.01, 2.16, 2.33 (100 K), and a strong signal at g = 2.02 below 20 K; (2) a cytochrome b, Fe-S-dependent fumarate reductase, and (3) a protein apparently linked to the sulfur oxidoreductase activity. In contrast to fumarate reductase, no type cytochrome was present in the fractions exhibiting sulfur oxidoreductase activity. The presence of Fe-S centers was demonstrated by electron paramagnetic resonance spectroscopy at 10 K. It is not clear whether the c-type cytochrome in the same fractions is part of the sulfur-reducing apparatus of Sp. 5175. [ABSTRACT FROM AUTHOR]

An increasing number of iron-sulfur (Fe-S) proteins are found in which the Fe-S cluster is not involved in net electron transfer, as it is in the majority of Fe-S proteins. Most of the former are (de)hydratases, of which the most extensively studied is aconitase. Approaches are described and discussed by which the Fe-S cluster of this enzyme could be brought into states of different structure, ligation, oxidation and isotope composition. The species, so obtained, provided the basis for spectroscopic and chemical investigations. Results from studies by protein chemistry, EPR, Mössbauer, ¹H, ²H and 57Fe electron-nuclear double resonance spectroscopy are described. Conclusions, which bear on the electronic structure of the Fe-S cluster, enzyme-substrate interaction and the enzymatic mechanism, were derived from a synopsis of the recent work described here and of previous contributions from several laboratories. These conclusions are discussed and summarized in a final section. [ABSTRACT FROM AUTHOR]

Extensively or completely activated preparations of beef heart succinate dehydrogenase have been investigated by electron paramagnetic resonance (EPR) techniques at 6 to 97 K. Reductive titrations with dithionite and rapid kinetic studies were performed with various types of soluble and membrane-bound preparations of the enzyme. The following components were detected and their behavior analyzed: a free radical, presumably arising from the covalently bound flavin on reduction, two iron-sulfur centers of the ferredoxin type, the signals of which appear on reduction, and a high-potential iron-sulfur component, detectable in the oxidized state. The high-potential component was only detected in complex II and inner-membrane preparations. This component and one of the ferredoxin­type centers were present in amounts close to stoichiometric with the flavin and were reduced by substrate. The other ferredoxin­type center was present in amounts between 0.1 and 0.5 times that of the flavin and was reduced only by dithionite. Of the components reduced by succinate, however, only a fraction (up to 50% of the high-potential iron-sulfur center and 40-60% of the ferredoxin­type iron-sulfur center) was reduced within the turnover time of the enzymes, in complex II not more than about 10% of the flavin appeared in the semiquinone form at any time. Soluble, purified preparations behaved similarly except that the high-potential component was nearly or completely absent and extensive accumulation of the free radical occurred (up to 70 to 80% of the flavin) in titration and kinetic experiments. No significant difference was observed between the rates of semiquinone formation and the reduction of the ferredoxin­type or high-potential centers by the substrate. Also no qualitative differences in the properties studied in this work became apparent between preparations containing 4 or 8 iron atoms, respectively. [ABSTRACT FROM AUTHOR]