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91.
C S Butler J M Charnock B Bennett H J Sears A J Reilly S J Ferguson C D Garner D J Lowe A J Thomson B C Berks D J Richardson 《Biochemistry》1999,38(28):9000-9012
The periplasmic nitrate reductase from Paracoccus denitrificans is a soluble two-subunit enzyme which binds two hemes (c-type), a [4Fe-4S] center, and a bis molybdopterin guanine dinucleotide cofactor (bis-MGD). A catalytic cycle for this enzyme is presented based on a study of these redox centers using electron paramagnetic resonance (EPR) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The Mo(V) EPR signal of resting NAP (High g [resting]) has g(av) = 1.9898 is rhombic, exhibits low anisotropy, and is split by two weakly interacting protons which are not solvent-exchangeable. Addition of exogenous ligands to this resting state (e.g., nitrate, nitrite, azide) did not change the form of the signal. A distinct form of the High g Mo(V) signal, which has slightly lower anisotropy and higher rhombicity, was trapped during turnover of nitrate and may represent a catalytically relevant Mo(V) intermediate (High g [nitrate]). Mo K-edge EXAFS analysis was undertaken on the ferricyanide oxidized enzyme, a reduced sample frozen within 10 min of dithionite addition, and a nitrate-reoxidized form of the enzyme. The oxidized enzyme was fitted best as a di-oxo Mo(VI) species with 5 sulfur ligands (4 at 2. 43 A and 1 at 2.82 A), and the reduced form was fitted best as a mono-oxo Mo(IV) species with 3 sulfur ligands at 2.35 A. The addition of nitrate to the reduced enzyme resulted in reoxidation to a di-oxo Mo(VI) species similar to the resting enzyme. Prolonged incubation of NAP with dithionite in the absence of nitrate (i.e., nonturnover conditions) resulted in the formation of a species with a Mo(V) EPR signal that is quite distinct from the High g family and which has a g(av) = 1.973 (Low g [unsplit]). This signal resembles those of the mono-MGD xanthine oxidase family and is proposed to arise from an inactive form of the nitrate reductase in which the Mo(V) form is only coordinated by the dithiolene of one MGD. In samples of NAP that had been reduced with dithionite, treated with azide or cyanide, and then reoxidized with ferricyanide, two Mo(V) signals were detected with g(av) elevated compared to the High g signals. Kinetic analysis demonstrated that azide and cyanide displayed competitive and noncompetitive inhibition, respectively. EXAFS analysis of azide-treated samples show improvement to the fit when two nitrogens are included in the molybdenum coordination sphere at 2.52 A, suggesting that azide binds directly to Mo(IV). Based on these spectroscopic and kinetic data, models for Mo coordination during turnover have been proposed. 相似文献
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93.
Gary Strobel Eric Booth George Schaible Morgan Tess Mends Joe Sears Brad Geary 《Biotechnology letters》2013,35(4):539-552
The construction and testing of a unique instrument, the Paleobiosphere, which mimics some of the conditions of the ancient earth, is described. The instrument provides an experimental testing system for determining if certain microbes, when provided an adequate environment, can degrade biological materials to produce fuel-like hydrocarbons in a relatively short time frame that become trapped by the shale. The conditions selected for testing included a particulate Montana shale (serving as the “Trap Shale”), plant materials (leaves and stems of three extant species whose origins are in the late Cretaceous), a water-circulating system, sterile air, and a specially designed Carbotrap through which all air was passed as exhaust and volatile were hydrocarbons trapped. The fungus for initial testing was Annulohypoxylon sp., isolated as an endophyte of Citrus aurantifolia. It produces, in solid and liquid media, a series of hydrocarbon-like molecules. Some of these including 1,8-cineole, 2-butanone, propanoic acid, 2-methyl-, methyl ester, benzene (1-methylethyl)-, phenylethyl alcohol, benzophenone and azulene, 1,2,3,5,6,7,8,8a-octahydro-1,4-dimethyl-7-(1-methylethenyl), [1S-(1α,7α,8aβ)]. These were the key signature compounds used in an initial Paleobiosphere test. After 3 weeks, incubation, the volatiles associated with the harvested “Trap Shale” included each of the signature substances as well as other fungal-associated products: some indanes, benzene derivatives, some cyclohexanes, 3-octanone, naphthalenes and others. The fungus thus produced a series of “Trap Shale” products that were representative of each of the major classes of hydrocarbons in diesel fuel (Mycodiesel). Initial tests with the Paleobiosphere offer some evidence for a possible origin of hydrocarbons trapped in bentonite shale. Thus, with modifications, numerous other tests can also be designed for utilization in the Paleobiosphere. 相似文献
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96.
G A Strobel E Ford J Y Li J Sears R S Sidhu W M Hess 《Systematic and applied microbiology》1999,22(3):426-433
Seimatoantlerium gen. nov., type species, S. tepuiense sp. nov. is proposed for an acervular fungus producing 4-septate, holoblastic conidia with 6-8 unbranched, apical appendages that dehisce as an appendage apparatus and also commonly possessing one or two exogenous basal appendages as well as a pedicel. It is compared with Seimatosporium, Seimatosporiopsis, and other genera. It is epiphytic on Maguireothamnus speciosus, a rubiaceous plant endemic to the tepuis of southeastern Venezuela. It produces the anti-oomycetous anticancer compound, taxol, as shown by immunological and spectroscopic methods. Taxol production is discussed relative to the ability of this fungus to exist in an extremely moist ecosystem, as well as to its relationship to other plant associated fungi. 相似文献
97.
98.
Chapman J Miles PD Ofrecio JM Neels JG Yu JG Resnik JL Wilkes J Talukdar S Thapar D Johnson K Sears DD 《PloS one》2010,5(11):e13959
Background
Insulin resistance is manifested in muscle, adipose tissue, and liver and is associated with adipose tissue inflammation. The cellular components and mechanisms that regulate the onset of diet-induced insulin resistance are not clearly defined.Methodology and Principal Findings
We initially observed osteopontin (OPN) mRNA over-expression in adipose tissue of obese, insulin resistant humans and rats which was normalized by thiazolidinedione (TZD) treatment in both species. OPN regulates inflammation and is implicated in pathogenic maladies resulting from chronic obesity. Thus, we tested the hypothesis that OPN is involved in the early development of insulin resistance using a 2–4 week high fat diet (HFD) model. OPN KO mice fed HFD for 2 weeks were completely protected from the severe skeletal muscle, liver and adipose tissue insulin resistance that developed in wild type (WT) controls, as determined by hyperinsulinemic euglycemic clamp and acute insulin-stimulation studies. Although two-week HFD did not alter body weight or plasma free fatty acids and cytokines in either strain, HFD-induced hyperleptinemia, increased adipose tissue inflammation (macrophages and cytokines), and adipocyte hypertrophy were significant in WT mice and blunted or absent in OPN KO mice. Adipose tissue OPN protein isoform expression was significantly altered in 2- and 4-week HFD-fed WT mice but total OPN protein was unchanged. OPN KO bone marrow stromal cells were more osteogenic and less adipogenic than WT cells in vitro. Interestingly, the two differentiation pathways were inversely affected by HFD in WT cells in vitro.Conclusions
The OPN KO phenotypes we report reflect protection from insulin resistance that is associated with changes in adipocyte biology and adipose tissue inflammatory status. OPN is a key component in the development of HFD-induced insulin resistance. 相似文献99.
Behavioral responses to biopsy sampling of four species of northwestern Atlantic balaenopterid whales summering in the estuary and Gulf of St. Lawrence, Quebec, from 1990 to 1995 were studied to determine if this technique was an important disturbance to the whales. A total of 447 biopsy samples were taken using a small punch-type biopsy tip fired from a crossbow. Biopsies were successfully taken from 91.2% of the whales approached. Whales displayed no reaction to 45.2% of the successful biopsy attempts. Whales that responded to biopsy sampling typically resumed their normal behavior immediately or within a few minutes. Most humpback whales displayed a hard tail flick, and the majority of fin and blue whales submerged following biopsy sampling. Significantly different frequencies and intensities of responses were found between whale species. Minke and humpback whales were found to be more sensitive to biopsy sampling than fin and blue whales. Response frequencies were similar between females and males for all species, with the exception of fin whales where females had a higher response frequency than males. Biopsy sample length, i. e., penetration depth, did not explain variations in response intensity but may influence response frequency to biopsy sampling. Group size, geographical region, and number of biopsies taken per whale were not factors that explained variation in behavioral responses. The biopsy technique was found to be an efficient method for obtaining high-quality whale skin and blubber samples with limited behavioral disturbance to balaenopterid whales. 相似文献
100.