The spin state of the heme in superoxide (O2*- )-producing cytochrome b558 purified from pig neutrophils was examined by means of room-temperature magnetic circular dichroism (MCD) under ...physiological conditions. Cytochrome b558 with varying amounts of low-spin and high-spin heme was prepared by either pH adjustment or heat treatment, and the O2*−-forming activity in a cell-free system was found to correlate with the low-spin heme content. The possibility that the O2*−-forming activity results from a transient high-spin ferric heme form that is induced during activation by anionic amphophils has also been investigated. EPR spectra of cytochrome b558 activated by either arachidonic acid or myristic acid, showed that a transient high-spin ferric species accounting for approximately 50%of the heme appeared in the presence of arachidonic acid, but not in the presence of myristic acid. Hence the appearance of a transient high-spin ferric heme species on activation with an amphophil does not afford a common activation mechanism in the NADPH oxidase system. The EPR results for cytochrome b558 activated with arachidonic acid showed that the transient high-spin ferric heme can bind cyanide. However, the high-spin ferric heme does not contribute to the O2*− production of cytochrome b558 in cell- free assays in the presence of cyanide.
We report the discovery of TeV gamma-ray emission coincident with the shell-type radio supernova remnant (SNR) CTA 1 using the VERITAS gamma-ray observatory. The source, VER J0006+729, was detected ...as a 6.5 standard deviation excess over background and shows an extended morphology, approximated by a two-dimensional Gaussian of semimajor (semiminor) axis 0 30 (0 24) and a centroid 5' from the Fermi gamma-ray pulsar PSR J0007+7303 and its X-ray pulsar wind nebula (PWN). The photon spectrum is well described by a power-law dN / dE = N 0 ( E /3 TeV) –Γ , with a differential spectral index of Γ = 2.2 ± 0.2 stat ± 0.3 sys , and normalization N 0 = (9.1 ± 1.3 stat ± 1.7 sys ) × 10 –14 cm –2 s –1 TeV –1 . The integral flux, F γ = 4.0 × 10 –12 erg cm –2 s –1 above 1 TeV, corresponds to 0.2% of the pulsar spin-down power at 1.4 kpc. The energetics, colocation with the SNR, and the relatively small extent of the TeV emission strongly argue for the PWN origin of the TeV photons. We consider the origin of the TeV emission in CTA 1.
We present the results of observations of the TeV binary LS I +61? 303 with the VERITAS telescope array between 2008 and 2010, at energies above 300 GeV. In the past, both ground-based gamma-ray ...telescopes VERITAS and MAGIC have reported detections of TeV emission near the apastron phases of the binary orbit. The observations presented here show no strong evidence for TeV emission during these orbital phases; however, during observations taken in late 2010, significant emission was detected from the source close to the phase of superior conjunction (much closer to periastron passage) at a 5.6 standard deviation (5.6 Delta *s) post-trials significance. In total, between 2008 October and 2010 December a total exposure of 64.5 hr was accumulated with VERITAS on LS I +61? 303, resulting in an excess at the 3.3 Delta *s significance level for constant emission over the entire integrated data set. The flux upper limits derived for emission during the previously reliably active TeV phases (i.e., close to apastron) are less than 5% of the Crab Nebula flux in the same energy range. This result stands in apparent contrast to previous observations by both MAGIC and VERITAS which detected the source during these phases at 10% of the Crab Nebula flux. During the two year span of observations, a large amount of X-ray data were also accrued on LS I +61? 303 by the Swift X-ray Telescope and the Rossi X-ray Timing Explorer Proportional Counter Array. We find no evidence for a correlation between emission in the X-ray and TeV regimes during 20 directly overlapping observations. We also comment on data obtained contemporaneously by the Fermi Large Area Telescope.
We report on the VERITAS observations of the high-frequency peaked BL Lac object 1ES 1959+650 in the period 2007-2011. This source is detected at TeV energies by VERITAS at 16.4 standard deviation ...(σ) significance in 7.6 hr of observation in a low flux state. A multiwavelength spectral energy distribution (SED) is constructed from contemporaneous data from VERITAS, Fermi -LAT, RXTE PCA, and Swift UVOT. Swift XRT data is not included in the SED due to a lack of simultaneous observations with VERITAS. In contrast to the orphan γ-ray flare exhibited by this source in 2002, the X-ray flux of the source is found to vary by an order of magnitude, while other energy regimes exhibit less variable emission. A quasi-equilibrium synchrotron self-Compton model with an additional external radiation field is used to describe three SEDs corresponding to the lowest, highest, and average X-ray states. The variation in the X-ray spectrum is modeled by changing the electron injection spectral index, with minor adjustments of the kinetic luminosity in electrons. This scenario produces small-scale flux variability of the order of 2 in the high energy ( E > 1 MeV) and very high energy ( E > 100 GeV) γ-ray regimes, which is corroborated by the Fermi -LAT, VERITAS, and Whipple 10 m telescope light curves.
We present observations of the BL Lac object 1ES 0414+009 in the >200 GeV gamma-ray band by the VERITAS array of Cherenkov telescopes. 1ES 0414+009 was observed by VERITAS between 2008 January and ...2011 February, resulting in 56.2 hr of good quality pointed observations. These observations resulted in a detection of 822 events from the source corresponding to a statistical significance of 6.4 standard deviations (6.4sigma) above the background. The source flux, showing no evidence for variability, is measured as (5.2 + or - 1.1 sub(stat) + or - 2.6 sub(sys)) x 10 super(-12) photons cm super(-2) s super(-1) above 200 GeV, equivalent to approximately 2% of the Crab Nebula flux above this energy. The differential photon spectrum from 230 GeV to 850 GeV is well fit by a power law with a photon index of Gamma = 3.4 + or - 0.5 sub(stat) + or - 0.3 sub(sys) and a flux normalization of (1.6 + or - 0.3 sub(stat) + or - 0.8 sub(sys)) x 10 super(-11) photons cm super(-2) s super(-1) at 300 GeV. We also present multiwavelength results taken in the optical (MDM), x-ray (Swift-XRT), and GeV (Fermi-LAT) bands and use these results to construct a broadband spectral energy distribution (SED). Modeling of this SED indicates that homogenous one-zone leptonic scenarios are not adequate to describe emission from the system, with a lepto-hadronic model providing a better fit to the data.
We report on very high energy (E > 100 GeV) gamma-ray observations of V407 Cygni, a symbiotic binary that underwent a nova outburst producing 0.1-10 GeV gamma rays during 2010 March 10-26. ...Observations were made with the Very Energetic Radiation Imaging Telescope Array System during 2010 March 19-26 at relatively large zenith angles due to the position of V407 Cyg. An improved reconstruction technique for large zenith angle observations is presented and used to analyze the data. We do not detect V407 Cygni and place a differential upper limit on the flux at 1.6 TeV of 2.3 x 10 super(-12) erg cm super(-2) s super(-1) (at the 95% confidence level). When considered jointly with data from Fermi-LAT, this result places limits on the acceleration of very high energy particles in the nova.
The 25-kDa subunit of the proton-translocating NADH-quinone oxidoreductase (NDH-1) of Paracoccus denitrificans has been expressed in Escherichia coli and purified to homogeneity. EPR studies of the ...reduced recombinant protein indicated that the expressed subunit contains a single 2Fe-2S cluster (Yano, T., Sled', V. D., Ohnishi, T., and Yagi, T. (1994) Biochemistry 33, 494-499). In this report, the electronic, magnetic, and vibrational properties of the 2Fe-2S2+,+ center have been investigated by the combination of absorption, circular dichroism, variable-temperature magnetic circular dichroism, electron paramagnetic resonance, and resonance Raman spectroscopies and compared with a range of simple 2Fe-2S-containing proteins. The results are consistent with coordination by two cysteinyl residues at both the reducible and nonreducible iron sites and reveal a striking similarity between the properties of the 2Fe-2S cluster in the P. denitrificans NDH-1 25-kDa subunit and those of the subclass of ferredoxin-type 2Fe-2S centers typified by Clostridium pasteurianum 2Fe ferredoxin. The four cyteines residues involved in cluster ligation in these proteins have been tentatively identified based on sequence homology considerations.
Certain inorganic salts are known to promote the development of charge separations during the linear freezing of their dilute solutions. These same salts strongly influence the morphology, the ...aggregation, and the secondary ice nucleation characteristics of growing single ice crystals in laboratory cloud chamber experiments. To explain these cloud chamber results, a mechanism for the development of the charge separations is proposed in which hydronium and hydroxyl ions are shown to be the potential-determining ions in a pH-dependent process. Electrochemical double layers are postulated to occur on the growing single crystal faces with anions or cations present as counterions in the double layers. This mechanism obviates the requirement for the inclusion of a wide range of chemically different anions and cations in the ice phase as advocated in previous publications.
Conformational dynamics within the complex between Zn-substituted cytochrome c peroxidase (ZnCcP) and cytochrome c (Cc) has been studied by examining the quenching of the super(3)ZnP excited state by ...the ferriheme of Cc.
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