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111.
Alessandro Vergara Marisa Franzese Giovanna Bonomi Daniela Giordano H. Caroline Lee Lelio Mazzarella 《Biophysical journal》2009,97(3):866-874
Oxidation of Hbs leads to the formation of different forms of Fe(III) that are relevant to a range of biochemical and physiological functions. Here we report a combined EPR/x-ray crystallography study performed at acidic pH on six ferric tetrameric Hbs. Five of the Hbs were isolated from the high-Antarctic notothenioid fishes Trematomus bernacchii, Trematomus newnesi, and Gymnodraco acuticeps, and one was isolated from the sub-Antarctic notothenioid Cottoperca gobio. Our EPR analysis reveals that 1), in all of these Hbs, at acidic pH the aquomet form and two hemichromes coexist; and 2), only in the three Hbs that exhibit the Root effect is a significant amount of the pentacoordinate (5C) high-spin Fe(III) form found. The crystal structure at acidic pH of the ferric form of the Root-effect Hb from T. bernacchii is also reported at 1.7 Å resolution. This structure reveals a 5C state of the heme iron for both the α- and β-chains within a T quaternary structure. Altogether, the spectroscopic and crystallographic results indicate that the Root effect and hemichrome stability at acidic pH are correlated in tetrameric Hbs. Furthermore, Antarctic fish Hbs exhibit higher peroxidase activity than mammalian and temperate fish Hbs, suggesting that a partial hemichrome state in tetrameric Hbs, unlike in monomeric Hbs, does not remove the need for protection from peroxide attack, in contrast to previous results from monomeric Hbs. 相似文献
112.
Kerstin Nicolaisen Marianne Valdebenito Anastazia Samborski Iris Maldener Ana Valladares Klaus Hantke 《生物化学与生物物理学报:生物膜》2010,1798(11):2131-2140
Iron uptake is essential for Gram-negative bacteria including cyanobacteria. In cyanobacteria, however, the iron demand is higher than in proteobacteria due to the function of iron as a cofactor in photosynthesis and nitrogen fixation, but our understanding of iron uptake by cyanobacteria stands behind the knowledge in proteobacteria. Here, two genes involved in this process in the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 were identified. ORF all4025 encodes SchE, a putative cytoplasmic membrane-localized transporter involved in TolC-dependent siderophore secretion. Inactivation of schE resulted in an enhanced sensitivity to high metal concentrations and decreased secretion of hydroxamate-type siderophores. ORF all4026 encodes a predicted outer membrane-localized TonB-dependent iron transporter, IacT. Inactivation of iacT resulted in decreased sensitivity to elevated iron and copper levels. Expression of iacT from the artificial trc promoter (Ptrc) resulted in sensitization against tested metals. Further analysis showed that iron and copper effects are synergistic because a decreased supply of iron induced a significant decrease of copper levels in the iacT insertion mutant but an increase of those levels in the strain carrying Ptrc-iacT. Our results unravel a link between iron and copper homeostasis in Anabaena sp. PCC 7120. 相似文献
113.
Ferric uptake regulator (Fur) proteins are widely recognized as repressors that in many prokaryotes regulate a large number of genes involved in iron homeostasis and oxidative stress response. In our study, we were able to identify the complete sequence of the fur gene from Microcystis aeruginosa using inverse-polymerase chain reaction. DNA sequence analysis confirmed the presence of a 183 amino-acid open reading frame that showed high identity with Fur proteins reported for cyanobacteria. The recombinant Fur protein has been purified and electrophoretical mobility shift assays shown to be active. Mn2+ and dithiothreitol enable Fur to bind to its promoter, with dithiothreitol being more potent. The expression of Fur in Microcystis was induced about twofold in iron-deficient conditions. 相似文献
114.
Claudiu T. Supuran Fabrizio Briganti Giovanna Mincione Andrea Scozzafava 《Journal of enzyme inhibition and medicinal chemistry》2013,28(2):111-128
L-alanine hydroxamate derivatives were obtained by reaction of alkyl/arylsulfonyl halides with L-alanine, followed by treatment with benzyl chloride, and conversion of the COOH moiety to the CONHOH group with hydroxylamine in the presence of carbodiimides. Other derivatives were obtained by reaction of N-benzyl-alanine with aryl isocyanates, arylsulfonyl isocyanates or benzoyl isothiocyanate, followed by a similar conversion of the COOH to the CONHOH moiety. The obtained compounds were assayed as inhibitors of Clostridium histolyticum collage-nase, ChC (EC 3.4.24.3), a zinc enzyme which degrades triple helical collagen. The hydroxamate derivatives were generally 100-500 times more active than the corresponding carboxylates. In the series of synthesized derivatives, substitution patterns leading to the most potent ChC inhibitors were those involving perfluoroalkylsulfonyl-and substituted-arylsulfonyl moieties, such as pentafluorophenylsulfonyl, 3- and 4-protected-aminophenylsulfonyl-, 3- and 4-carboxy-phenylsulfonyl-, 3-trifluoromethyl-phenylsulfonyl-, or 1- and 2-naphthylsulfonyl among others. Similarly to the matrix metalloproteinase (MMP) hydroxamate inhibitors, ChC inhibitors of the type reported here must incorporate hydrophobic moieties at the P2, and P3 sites, in order to achieve tight binding to the enzyme. 相似文献
115.
F. G. Ferris 《Geomicrobiology journal》2013,30(3-4):79-85
Bacteriogenic iron oxides (BIOS) are composite materials that consist of intact and partly degraded remains of bacterial cells intermixed with variable amounts of poorly ordered hydrous ferric oxide (HFO) minerals. They form in response to chemical or bacterial oxidation of Fe2+, which gives rise to Fe3+. Once formed, Fe3+ tends to undergo hydrolysis to precipitate in association with bacterial cells. In acidic systems where the chemical oxidation of Fe2+ is slow, bacteria are capable of accelerating the reaction by several orders of magnitude. At circumneutral pH, the chemical oxidation of Fe2+ is fast. This requires Fe2+ oxidizing bacteria to exploit steep redox gradients where low pO2 slows the abiotic reaction enough to allow the bacteria to compete kinetically. Because of their reactive surface properties, BIOS behave as potent sorbents of dissolved metal ions. Strong enrichments of Al, Cu, Cr, Mn, Sr, and Zn in the solid versus aqueous phase (log 10 Kd values range from 1.9 to 4.2) are common; however, the metal sorption properties of BIOS are not additive owing to surface chemical interactions between the constituent HFO and bacteria. These interactions have been investigated using acid-base tritrations, which show that the concentration of high pKa sites is reduced in BIOS compared to HFO. At the same time, hydroxylamine insoluble material (i.e., residual bacterial fraction) is enriched in low pKa sites relative to both BIOS and HFO. These differences indicate that low pKa or acidic sites associated with bacteria in BIOS interact specifically with high pKa or basic sites on intermixed HFO. 相似文献
116.
Ascenzi P Ciaccio C Sinibaldi F Santucci R Coletta M 《Biochemical and biophysical research communications》2011,(3):463-467
Carboxymethylation of equine heart cytochrome c (cytc) changes its tertiary structure by disrupting the heme-Fe-Met80 distal bond, such that carboxymethylated cytc (CM-cytc) displays myoglobin-like properties. Here, the effect of cardiolipin (CL) on peroxynitrite isomerization by ferric CM-cytc (CM-cytc-Fe(III)) is reported. Unlike native ferric cytc (cytc-Fe(III)), CM-cytc-Fe(III) catalyzes peroxynitrite isomerization, the value of the second order rate constant (kon) is 6.8 × 104 M−1 s−1. However, CM-cytc-Fe(III) is less effective in peroxynitrite isomerization than CL-bound cytc-Fe(III) (CL-cytc-Fe(III); kon = 3.2 × 105 M−1 s−1). Moreover, CL binding to CM-cytc-Fe(III) facilitates peroxynitrite isomerization (kon = 5.3 × 105 M−1 s−1). Furthermore, the value of the dissociation equilibrium constant for CL binding to CM-cytc-Fe(III) (K = 1.8 × 10−5 M) is lower than that reported for CL-cytc-Fe(III) complex formation (K = 5.1 × 10−5 M). Although CM-cytc-Fe(III) and CL-cytc-Fe(III) display a different heme distal geometry and heme-Fe(III) reactivity, the heme pocket and the CL cleft are allosterically linked. 相似文献
117.
118.
Lewis E. Fox 《Hydrobiologia》1993,253(1-3):1-16
Phosphate levels in turbid rivers with low calcium concentrations are controlled by a solid ferric hydroxide-phosphate solution present in colloidal suspensions or suspended particulates. A chemical model, based on this behavior, is consistent with data from dialyzed suspensions of iron and phosphorus prepared in the laboratory as well as from the Amazon, Zaire, Orinoco, Sepik, Delaware, Hudson, Negro, and Mullica rivers. Data indicate that solid Fe/P ratios are related to solid activity coefficients by an exponential parameter, y, which represents the deviation of solid-solution from ideality. The model is mathematically consistent with Langmuir and Freundlich sorption isotherms under equilibrium conditions, and demonstrates that the isotherm parameters consist of a combination of selected constants and variables defined by solution theory. The reciprocal of the model parameter-y is shown to be equivalent to the exponential parameter in a Freundlich isotherm. The Langmuir parameter and Freundlich exponential parameter are related through the model parameter-y in systems at constant pH and ionic strength.From a presentation given at the Third International Workshop on Phosphorus in Sediments, Woudscholten/Utrecht, The Netherlands, September 30, 1991, under the auspices of: International Association of Theoretical and Applied Limnology, Limnological Institute (Royal Netherlands Academy of Arts and Sciences), Institute for Inland Water Management and Waste Water Treatment, and the Netherlands Institute for Sea Research. 相似文献
119.
儿茶素的抑菌作用及其与铁离子相互作用研究 总被引:2,自引:0,他引:2
采用微生物学方法检测了儿茶素对 4种细菌的抑制作用以及采用UV -VIS光谱法研究了儿茶素在铁离子介导下的促氧化作用 ,提出了儿茶素抑菌作用和促氧化作用的可能机制。 相似文献
120.
Iron homeostasis is, in many bacterial species, mediated by the ferric uptake regulator (Fur). A regulatory site able to bind iron to activate Fur for DNA binding has been described, and a structural zinc site essential for the dimerization has also been proposed. They have been localized and named site 1 and site 2, respectively, from the crystal structure of a zinc-substituted Pseudomonas aeruginosa Fur (PA-Fur). Notwithstanding the studies on Fur proteins from various species, both the precise site of iron binding and the effect on DNA binding affinity are still controversial. These issues were investigated here by molecular dynamics simulations and free energy calculations. Simulations were performed for eight molecular systems represented by the three forms of Fur, that is, apo Fur, metal-substituted Fur, and Fur complexed with DNA. Because of the lack of a Fur-DNA complex crystal structure, the recently published model based on mass spectrometry experiments on Escherichia coli Fur (EC-Fur), and the crystal structure of PA-Fur, was used, after adjustment to adopt a symmetric conformation. The simulation results suggest that the formerly proposed site 2 is, in fact, the regulatory iron-sensing site. The calculations also predict that Fe(2+) at site 2 is hexacoordinated having an octahedral environment with only nitrogen and oxygen atoms, which is in accordance with previous spectroscopic characterizations. Energy decomposition pinpoints H87 as an additional amino acid that defines the regulatory metal site. Finally, free energy decomposition analysis reveals a number of amino acids potentially important in dimerization and in DNA binding. 相似文献