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Sulfur Clusters (sulfur + cluster)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

Fourier transform Raman spectroscopic study of pressure-induced ligand bond activation in a molybdenum,sulfur cluster,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2002
Ian S. Butler
Fourier transform Raman spectra of the prototype, triangular, transition metal,sulfur cluster anion [Mo3(S2)6S]2, were recorded at pressures up to 60 kbar with the aid of a diamond-anvil cell (DAC). The pressure dependences (,,/,p) of the Raman bands indicate a structural change at around 10,15 kbar. The SS stretching mode for the bridging disulfide ligands exhibits a slightly negative ,,/,p value (,0.08), suggesting that SS bonds are weakened, i.e. activated, at high pressures. This pressure-induced activity parallels the observed nucleophilic substitution reactivity of the S2 groups in this molybdenum cluster anion. In view of this, a preliminary investigation of the reaction between [Mo3(S2)6S]2, and CN, was undertaken in the solid state in the DAC under high pressure. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Adenosyl Radical: Reagent and Catalyst in Enzyme Reactions

CHEMBIOCHEM, Issue 5 2010
E. Neil G. Marsh Prof.
Abstract Adenosine is undoubtedly an ancient biological molecule that is a component of many enzyme cofactors: ATP, FADH, NAD(P)H, and coenzyme A, to name but a few, and, of course, of RNA. Here we present an overview of the role of adenosine in its most reactive form: as an organic radical formed either by homolytic cleavage of adenosylcobalamin (coenzyme B12, AdoCbl) or by single-electron reduction of S -adenosylmethionine (AdoMet) complexed to an iron,sulfur cluster. Although many of the enzymes we discuss are newly discovered, adenosine's role as a radical cofactor most likely arose very early in evolution, before the advent of photosynthesis and the production of molecular oxygen, which rapidly inactivates many radical enzymes. AdoCbl-dependent enzymes appear to be confined to a rather narrow repertoire of rearrangement reactions involving 1,2-hydrogen atom migrations; nevertheless, mechanistic insights gained from studying these enzymes have proved extremely valuable in understanding how enzymes generate and control highly reactive free radical intermediates. In contrast, there has been a recent explosion in the number of radical-AdoMet enzymes discovered that catalyze a remarkably wide range of chemically challenging reactions; here there is much still to learn about their mechanisms. Although all the radical-AdoMet enzymes so far characterized come from anaerobically growing microbes and are very oxygen sensitive, there is tantalizing evidence that some of these enzymes might be active in aerobic organisms including humans. [source]

Folding and turnover of human iron regulatory protein 1 depend on its subcellular localization

FEBS JOURNAL, Issue 4 2007
Alain Martelli
Aconitases are iron,sulfur hydrolyases catalysing the interconversion of citrate and isocitrate in a wide variety of organisms. Eukaryotic aconitases have been assigned additional roles, as in the case of the metazoan dual activity cytosolic aconitase,iron regulatory protein 1 (IRP1). This human protein was produced in yeast mitochondria to probe IRP1 folding in this organelle where iron,sulfur synthesis originates. The behaviour of human IRP1 was compared with that of genuine mitochondrial (yeast or human) aconitases. All enzymes were functional in yeast mitochondria, but IRP1 was found to form dense particles as detected by electron microscopy. MS analysis of purified inclusion bodies evidenced the presence of human IRP1 and ,-ketoglutarate dehydrogenase complex component 1 (KGD1), one of the subunits of ,-ketoglutarate dehydrogenase. KGD1 triggered formation of the mitochondrial aggregates, because the latter were absent in a KGD1, mutant, but it did not efficiently do so in the cytosol. Despite the iron-binding capacity of IRP1 and the readily synthesis of iron,sulfur clusters in mitochondria, the dense particles were not iron-rich, as indicated by elemental analysis of purified mitochondria. The data show that proper folding of dual activity IRP1-cytosolic aconitase is deficient in mitochondria, in contrast to genuine mitochondrial aconitases. Furthermore, efficient clearance of the aggregated IRP1,KGD1 complex does not occur in the organelle, which emphasizes the role of molecular interactions in determining the fate of IRP1. Thus, proper folding of human IRP1 strongly depends on its cellular environment, in contrast to other members of the aconitase family. [source]

Bacterial IscU is a well folded and functional single domain protein

FEBS JOURNAL, Issue 11 2004
Salvatore Adinolfi
Iron,sulfur clusters are widely represented in most organisms, but the mechanism of their formation is not fully understood. Of the two main proteins involved in cluster formation, NifS/IscS and NifU/IscU, only the former has been well studied from a structural point of view. Here we report an extensive structural characterization of Escherichia coli IscU. We show by a variety of physico-chemical techniques that E. coli IscU construct can be expressed to high purity as a monomeric protein, characterized by an ,, fold with high ,-helix content. The high melting temperature and the reversibility of the thermal unfolding curve (as measured by CD spectroscopy) hint at a well ordered stable fold. The excellent dispersion of cross peaks in the 1H- 15N correlation spectrum is consistent with these observations. Monomeric E. coli IscU is able to provide a scaffold for Iron,sulfur cluster assembly, but has no direct interaction with either Fe(II) or Fe(III) ions, suggesting the need of further partners to achieve a stable interaction. [source]

Enzymatic activation of sulfur for incorporation into biomolecules in prokaryotes

FEMS MICROBIOLOGY REVIEWS, Issue 6 2006
Dorothea Kessler
Abstract Sulfur is a functionally important element of living matter. Incorporation into biomolecules occurs by two basic strategies. Sulfide is added to an activated acceptor in the biosynthesis of cysteine, from which methionine, coenzyme A and a number of biologically important thiols can be constructed. By contrast, the biosyntheses of iron sulfur clusters, cofactors such as thiamin, molybdopterin, biotin and lipoic acid, and the thio modification of tRNA require an activated sulfur species termed persulfidic sulfur (R-S-SH) instead of sulfide. Persulfidic sulfur is produced enzymatically with the IscS protein, the SufS protein and rhodanese being the most prominent biocatalysts. This review gives an overview of sulfur incorporation into biomolecules in prokaryotes with a special emphasis on the properties and the enzymatic generation of persulfidic sulfur as well as its use in biosynthetic pathways. [source]