Origin of graphitic carbon and pentlandite in matrix olivines in the Allende meteorite.
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Matrix olivines in the Allende carbonaceous chondrite are believed to have formed by condensation processes in the primitive solar nebula. However, transmission electron microscope observations of numerous matrix olivines show that they contain abundant, previously unrecognized, nanometer-sized inclusions of pentlandite and poorly graphitized carbon. Neither of these phases would have been stable at the high-temperature conditions required to condense iron-rich olivine in the solar nebula. The presence of these inclusions is consistent with formation of the olivines by parent body processes that involved overgrowth of fine-grained organic materials and sulfides in the precursor matrix materials. (+info)
The effect of iron on the toxigenicity of Vibrio cholerae.
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In vitro and in vivo studies were conducted to assess the response of cholera toxin (CT) production to increasing iron concentrations in an aquatic environment. Production of CT by seven of eight Vibrio cholerae strains tested, including the Bengal strain (O139), was significantly enhanced in the presence of iron concentrations of 1.0 and 10 g/L. The exception (El Tor Ogawa) had a significant CT response only in the presence of 10 g of iron/L. Enhancement of CT production also occurred at iron concentrations less than 1.0 g/L, but not to a statistically significant degree. The high iron concentrations, which in this study were found to stimulate CT production, have been described by others in association with sediments, water plants, and chitinous fauna. Other investigators have shown a predilection by V. cholerae to attach to these sites in the aquatic environment. The importance of excess in vivo iron with respect to the pathogenicity of several gram-negative bacilli is well recognized. However, the possible impact of environmental iron on the in vitro toxigenicity of a microorganism, in this case V. cholerae in its aquatic environment, is to the best of our knowledge a new finding with important epidemiologic implications. These findings, coupled with the fact that iron concentration is considerably enhanced in industrially polluted waters and sediments, may reflect a causal link between the concurrent global upsurge of industrialization and pandemic occurrence of cholera during the latter half of the 20th century. Enhanced toxigenicity may also cause clinical disease following ingestion of lower than usual infective doses of cholera vibrios, thereby increasing the incidence of symptomatic cases and, possibly, of severe cases. (+info)
Inhibition of iron-molybdenum cofactor biosynthesis by L127Delta NifH and evidence for a complex formation between L127Delta NifH and NifNE.
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Besides serving as the obligate electron donor to dinitrogenase during nitrogenase turnover, dinitrogenase reductase (NifH) is required for the biosynthesis of the iron-molybdenum cofactor (FeMo-co) and for the maturation of alpha(2)beta(2) apo-dinitrogenase (apo-dinitrogenase maturation). In an attempt to understand the role of NifH in FeMo-co biosynthesis, a site-specific altered form of NifH in which leucine at position 127 has been deleted, L127Delta, was employed in in vitro FeMo-co synthesis assays. This altered form of NifH has been shown to inhibit substrate reduction by the wild-type nitrogenase complex, forming a tight protein complex with dinitrogenase. The L127Delta NifH was found to inhibit in vitro FeMo-co synthesis by wild-type NifH as detected by the gamma gel shift assay. Increasing the concentration of NifNE and NifB-cofactor (NifB-co) relieved the inhibition of FeMo-co synthesis by L127Delta NifH. The formation of a complex of L127Delta NifH with NifNE was investigated by gel filtration chromatography. We herein report the formation of a complex between L127Delta NifH and NifNE in the presence of NifB-co. This work presents evidence for one of the possible roles for NifH in FeMo-co biosynthesis, i.e. the interaction of NifH with a NifNE.NifB-co complex. (+info)
Cardiovascular evidence for an intermediate or higher metabolic rate in an ornithischian dinosaur.
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Computerized tomography scans of a ferruginous concretion within the chest region of an ornithischian dinosaur reveal structures that are suggestive of a four-chambered heart and a single systemic aorta. The apparently derived condition of the cardiovascular system in turn suggests the existence of intermediate-to-high metabolic rates among dinosaurs. (+info)
Aggregation-based crystal growth and microstructure development in natural iron oxyhydroxide biomineralization products.
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Crystals are generally considered to grow by attachment of ions to inorganic surfaces or organic templates. High-resolution transmission electron microscopy of biomineralization products of iron-oxidizing bacteria revealed an alternative coarsening mechanism in which adjacent 2- to 3-nanometer particles aggregate and rotate so their structures adopt parallel orientations in three dimensions. Crystal growth is accomplished by eliminating water molecules at interfaces and forming iron-oxygen bonds. Self-assembly occurs at multiple sites, leading to a coarser, polycrystalline material. Point defects (from surface-adsorbed impurities), dislocations, and slabs of structurally distinct material are created as a consequence of this growth mechanism and can dramatically impact subsequent reactivity. (+info)
Oxidation of nitroxyl anion to nitric oxide by copper ions.
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1. This study made use of a nitric oxide-sensitive electrode to examine possible means of generating nitric oxide from nitroxyl anion (NO(-)) released upon the decomposition of Angeli's salt. 2. Our results show that copper ions (from CuSO(4)) catalyze the rapid and efficient oxidation of nitroxyl to nitric oxide. Indeed, the concentrations of copper required to do so (0.1 - 100 microM) are roughly 100-times lower than those required to generate equivalent amounts of nitric oxide from S-nitroso-N-acetyl-D,L-penicillamine (SNAP). 3. Experiments with ascorbate (1 mM), which reduces Cu(2+) ions to Cu(+), and with the Cu(2+) chelators, EDTA and cuprizone, and the Cu(+) chelator, neocuproine, each at 1 mM, suggest that the oxidation is catalyzed by copper ions in both valency states. 4. Some compounds containing other transition metals, i.e. methaemoglobin, ferricytochrome c and Mn(III)TMPyP, were much less efficient than CuSO(4) in catalyzing the formation of nitric oxide from nitroxyl, while FeSO(4), FeCl(3), MnCl(2), and ZnSO(4) were inactive. 5. Of the copper containing enzymes examined, Cu-Zn superoxide dismutase and ceruloplasmin were weak generators of nitric oxide from nitroxyl, even at concentrations (2500 and 30 u ml(-1), respectively) vastly greater than are present endogenously. Two others, ascorbate oxidase (10 u ml(-1)) and tyrosinase (250 u ml(-1)) were inactive. 6. Our findings suggest that a copper-containing enzyme may be responsible for the rapid oxidation of nitroxyl to nitric oxide by cells, but the identity of such an enzyme remains elusive. (+info)
Novel activation of non-selective cationic channels by dinitrosyl iron-thiosulfate in PC12 cells.
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Low molecular mass dinitrosyl iron complexes (DNICs) are nitrosating agents and it is known that the dinitrosyl iron moiety can be transferred to proteins. The aim of the present study was to determine if the formation of protein-bound dinitrosyl iron can modulate ionic channel activity. In PC12 cells, dinitrosyl iron-thiosulfate (50 microM) caused irreversible activation of a depolarizing inward current (IDNIC). IDNIC was partially inhibited by the metal chelator diethyldithiocarbamate (DETC, 1 mM), but not by the reducing/denitrosylating agent dithiothreitol (DTT, 5 mM). The activation of IDNIC was not reproduced by application of nitric oxide (NO., 100 microM), S-nitrocysteine (200 microM) or ferrous iron-thiosulfate (50 microM), and was not prevented by the irreversible guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one (ODQ, 1 microM). Similarly, intracellular perfusion of dinitrosyl iron-thiosulfate (100 microM) did not result in activation of IDNIC. Ion replacement experiments show that the DETC-sensitive component of IDNIC is a non-selective cationic current. In accordance, IDNIC was blocked by antagonists of receptor-operated calcium entry, gadolinium (25 microM) and SK&F 96365 (25 microM). Single-channel measurements from outside-out patches reveal that the DETC-sensitive component of IDNIC is an inward current carried by a cationic channel having a conductance of 50 pS. The present observations suggest that the formation of ion channel-bound dinitrosyl iron represents another mechanism of regulation of ion channel activity by NO.-related species, which may be particularly important in pathophysiological processes where NO. is overproduced. (+info)
Bacterial recognition of mineral surfaces: nanoscale interactions between Shewanella and alpha-FeOOH.
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Force microscopy has been used to quantitatively measure the infinitesimal forces that characterize interactions between Shewanella oneidensis (a dissimilatory metal-reducing bacterium) and goethite (alpha-FeOOH), both commonly found in Earth near-surface environments. Force measurements with subnanonewton resolution were made in real time with living cells under aerobic and anaerobic solutions as a function of the distance, in nanometers, between a cell and the mineral surface. Energy values [in attojoules (10(-18) joules)] derived from these measurements show that the affinity between S. oneidensis and goethite rapidly increases by two to five times under anaerobic conditions in which electron transfer from bacterium to mineral is expected. Specific signatures in the force curves suggest that a 150-kilodalton putative iron reductase is mobilized within the outer membrane of S. oneidensis and specifically interacts with the goethite surface to facilitate the electron transfer process. (+info)