921 research outputs found
Carbon Monoxide-Driven Reduction of Ferric Heme and Heme Proteins
Oxidized cytochrome c oxidase in a carbon monoxide atmosphere slowly becomes reduced as shown by changes in its visible spectra and its reactivity toward oxygen. The \u27autoreduction\u27 of cytochrome c oxidase by this procedure has been used to prepare mixed valence hybrids. We have found that this process is a general phenomenon for oxygen-binding heme proteins, and even for isolated hemin in basic aqueous solution. This reductive reaction may have physiological significance. It also explains why oxygen-binding heme proteins become oxidized much more slowly and appear to be more stable when they are kept under a CO atmosphere. Oxidized α and β chains of human hemoglobin become reduced under CO much more slowly than does cytochrome c oxidase, where the CO-binding heme is coupled with another electron accepting metal center. By observing the reaction in both the forward and reverse direction, we have concluded that the heme is reduced by an equivalent of the water-gas shift reaction (CO + H2O → CO2 + 2e- + 2H+). The reaction does not require molecular oxygen. However, when the CO-driven reduction of cytochrome c oxidase occurs in the presence of oxygen, there is a competition between CO and oxygen for the reduced heme and copper of cytochrome a3. Under certain conditions when both CO and oxygen are present, a peroxide adduct derived from oxygen reduction can be observed. This \u27607 nm complex\u27, described in 1981 by Nicholls and Chanady, forms and decays with kinetics in accord with the rate constants for CO dissociation, oxygen association and reduction, and dissociation of the peroxide adduct. In the absence of oxygen, if a mixture of cytochrome c and cytochrome c oxidase is incubated under a CO atmosphere, autoreduction of the cytochrome c as well as of the cytochrome c oxidase occurs. By our proposed mechanism this involves a redistribution of electrons from cytochrome a3 to cytochrome a and cytochrome c
Kinetics of Reduction of Cytochrome \u3ci\u3ec\u3c/i\u3e Oxidase by Dithionite and the Effect of Hydrogen Peroxide
The reduction of cytochrome c oxidase by dithionite was reinvestigated with a flow-flash technique and with varied enzyme preparations. Since cytochrome a3 may be defined as the heme in oxidase which can form a photolabile CO adduct in the reduced state, it is possible to follow the time course of cytochrome a3 reduction by monitoring the onset of photosensitivity. The onset of photosensitivity and the overall rate of heme reduction were compared for Yonetani and Hartzell-Beinert preparations of cytochrome c oxidase and for the enzyme isolated from blue marlin and hammer-head shark. For all of these preparations the faster phase of heme reduction, which is dithionite concentration-dependent, is almost completed when the fraction of photosensitive material is still small. We conclude that cytochrome a3 in the resting enzyme is consistently reduced by an intramolecular electron transfer mechanism. To determine if this is true also for the pulsed enzyme, we examined the time course of dithionite reduction of the peroxide complex of the pulsed enzyme. It has been previously shown that pulsed cytochrome c oxidase can interact with H2O2 and form a stable room temperature peroxide adduct (Bickar, D., Bonaventura, J., and Bonaventura, C. (1982) Biochemistry 21, 2661-2666). Rather complex kinetics of heme reduction are observed when dithionite is added to enzyme preparations that contain H2O2. The time courses observed provide unequivocal evidence that H2O2 can, under these conditions, be used by cytochrome c oxidase as an electron acceptor. Experiments carried out in the presence of CO show that a direct dithionite reduction of cytochrome a3 in the peroxide complex of the pulsed enzyme does not occur
Multilayer shallow water models with locally variable number of layers and semi-implicit time discretization
We propose an extension of the discretization approaches for multilayer
shallow water models, aimed at making them more flexible and efficient for
realistic applications to coastal flows. A novel discretization approach is
proposed, in which the number of vertical layers and their distribution are
allowed to change in different regions of the computational domain.
Furthermore, semi-implicit schemes are employed for the time discretization,
leading to a significant efficiency improvement for subcritical regimes. We
show that, in the typical regimes in which the application of multilayer
shallow water models is justified, the resulting discretization does not
introduce any major spurious feature and allows again to reduce substantially
the computational cost in areas with complex bathymetry. As an example of the
potential of the proposed technique, an application to a sediment transport
problem is presented, showing a remarkable improvement with respect to standard
discretization approaches
Keck Imaging of Binary L Dwarfs
We present Keck near-infrared imaging of three binary L dwarf systems, all of
which are likely to be sub-stellar. Two are lithium dwarfs, and a third
exhibits an L7 spectral type, making it the coolest binary known to date. All
have component flux ratios near 1 and projected physical separations between 5
and 10 AU, assuming distances of 18 to 26 pc from recent measurements of
trigonometric parallax. These surprisingly similar binaries represent the sole
detections of companions in ten L dwarf systems which were analyzed in the
preliminary phase of a much larger dual-epoch imaging survey. The detection
rate prompts us to speculate that binary companions to L dwarfs are common,
that similar-mass systems predominate, and that their distribution peaks at
radial distances in accord both with M dwarf binaries and with the radial
location of Jovian planets in our own solar system. To fully establish these
conjectures against doubts raised by biases inherent in this small preliminary
survey, however, will require quantitative analysis of a larger volume-limited
sample which has been observed with high resolution and dynamic range.Comment: LaTex manuscript in 13 pages, 3 postscript figures, Accepted for
publication in the Letters of the Astrophysical Journal; Postscript pre-print
version available at: http://www.hep.upenn.edu/PORG/papers/koerner99a.p
Association between interleukin-10 polymorphisms and Alzheimer's disease: a systematic review and meta-analysis
It has been hypothesized that polymorphisms of interleukin (IL)-10 genes affect the risk of developing late onset Alzheimer's disease (AD). However, results of different studies are often inconsistent. Our aim was to investigate by meta-analysis the association of the common polymorphisms comprehensively defining the genetic variability of the IL-10 gene with AD risk. Fifteen studies investigating the association between IL-10 polymorphisms (-1082,-819,-592) and AD were found and analyzed. The model-free approach was applied to meta-analyze these case-control genetic association studies. Available data suggested an association between-1082 polymorphism and AD risk with a marginal statistical significance (GG versus AG/AA: pooled odds ratio [OR]: 0.82, 95% confidence interval CI: 0.65-1.02) and evidence of a moderate degree of between-study heterogeneity (χ 2 = 27.13, d.f. = 13, p = 0.01, I 2 = 52%). For the-819 and-592 polymorphisms, we did not find an association with AD, but significant between-study heterogeneity made genotype data pooling unacceptable. Analysis by IL-10 haplotype showed that the-1082G/-819C/-592C haplotype is associated with a lower risk of AD, although with a marginal statistical significance, probably due to the low number of studies included (GCC versus other genotypes: OR: 0.61, 95% CI: 0.32-1.15; I 2: 85%). Current findings suggest a possible association between-1082 A > G polymorphism and the risk of developing AD; this effect is more evident in the oldest patients. The high degree of between-study heterogeneity, due to several underpowered studies and to other methodological problems of individual studies underlies the need for further methodologically adequate studies. © 2012-IOS Press and the authors. All rights reserved
Immunohistochemical expression and distribution of orexin, orphanin and leptin in the major salivary glands of some mammals
Abstract: The aim of the study was to assess the involvement of apoptotic factors, cytokeratins and metalloproteinase-
9 in the histogenesis of both Epithelialized Gingival Lesions (EGL) and Periapical Lesions (PAL).
55 consecutive patients, 30 with PAL and 25 with EGL, were selected for the study after clinical and radiological
examinations. The PAL patients had severe periapical lesions and tooth decay with exposure of the pulp chamber.
All PAL and EGL biopsies were surgically extracted, fixed in 10% buffered formalin, and processed for
routine light microscopy. Ten biopsies of each category were processed for immunohistochemistry (IHC). Serial
paraffin sections were stained by IHC with appropriate antibodies to detect cytokeratins (CKs) 1, 5, 8, 10 and 14,
caspase-3 and -9, metalloproteinase-9, and for PCNA and TUNEL assays. Both PAL and EGL showed a high
expression of the cytokeratin 1, 5 and 8 with higher expression in EGL. Moreover, CK10 was markedly less
intense expressed in EGL compared to PAL, while CK14 was almost three times stronger expressed in EGL.
The expression of caspase-3 and -9 was stronger in PAL compared to EGL, however, the difference was only
significant for caspase-9. In PAL apoptosis detected by TUNNEL method and the expression of MMP-9 were
higher than in EGL, whereas PCNA was significantly more expressed in EGL. The results clearly suggest that
both lesions have exclusively an epithelial origin and that epithelial proliferation was correlated with the degree
of apoptosis in both entities. PAL and EGL presented mostly similar cytokeratin expression except for CK10
and CK14, though with marked differences in the distribution and intensity of IHC reactions. Finally, the degradation
of extracellular matrix in both lesions could be partially attributed to the strong presence of MMP-9.
(Folia Histochemica et Cytobiologica 2012, Vol. 50, No. 4, 497–503)The aim of the study was to determine by immunochemistry the expression of leptin, orexin A and
orphanin FQ in the major salivary glands (parotid, submandibular and sublingual) of rat, sheep and cow. These
peptides, originally synthesized in central nervous system, adipose tissue and peripheral tissues including gastrointestinal
tract, play an orexigenic (orphanin and orexin) or anorexigenic (leptin) roles in the intricate neuronal
network appointed to the control of nutritional homeostasis. Peptide-specific immunoreactivity was present
in the studied salivary glands with various intensities in different species, in the ductal epithelium, sometimes in
the acinar epithelium, and in nervous trunks spread in connective tissue stroma. The obtained data show that
salivary glands present an unexpected source of orexigenic and anorexigenic peptides which with their autocrine,
paracrine, and endocrine mechanisms of action may participate in the control of salivary gland function
Iris: an Extensible Application for Building and Analyzing Spectral Energy Distributions
Iris is an extensible application that provides astronomers with a
user-friendly interface capable of ingesting broad-band data from many
different sources in order to build, explore, and model spectral energy
distributions (SEDs). Iris takes advantage of the standards defined by the
International Virtual Observatory Alliance, but hides the technicalities of
such standards by implementing different layers of abstraction on top of them.
Such intermediate layers provide hooks that users and developers can exploit in
order to extend the capabilities provided by Iris. For instance, custom Python
models can be combined in arbitrary ways with the Iris built-in models or with
other custom functions. As such, Iris offers a platform for the development and
integration of SED data, services, and applications, either from the user's
system or from the web. In this paper we describe the built-in features
provided by Iris for building and analyzing SEDs. We also explore in some
detail the Iris framework and software development kit, showing how astronomers
and software developers can plug their code into an integrated SED analysis
environment.Comment: 18 pages, 8 figures, accepted for publication in Astronomy &
Computin
Carbon capture and utilization for sodium bicarbonate production assisted by solar thermal power
In this paper, a novel carbon capture and utilization process is proposed. It is based on using a fraction of the captured carbon dioxide to produce sodium bicarbonate, a widely used product in the chemical and food industries. The process couples the Dry Carbonate process for carbon dioxide capture with sodium bicarbonate production. Raw material is trona or sodium sesquicarbonate dehydrate, which is a relatively abundant mineral composed by approximately 46% sodium carbonate and 35% sodium bicarbonate by weight. In the process, trona is firstly converted into sodium carbonate in a fluidized bed reactor operated at 180–200 °C and 1 bar. Heat required in the fluidized bed reactor for decomposing trona can be supplied by renewable sources such as low/medium temperature solar energy or biomass. A fraction of the sodium carbonate generated is recirculated for carbon dioxide capture by means of the dry carbonate process. The rest is converted to sodium bicarbonate in a carbonating tower through the reaction with carbon dioxide and water. After separation of sodium bicarbonate and other salts from water, the sodium bicarbonate produced is suitable for direct sale. The use of renewable sources for supplying the energy required at the sorbent regenerator and for trona decomposition yields a near-zero carbon dioxide emissions global system. As case of study, carbon dioxide capture coupled to sodium bicarbonate production has been analysed for a 15 MWel coal fired power plant. Heat required in the carbon capture process penalizes the global system efficiency by a 10.2%, which is reduced just to the electricity parasitic consumption for solids transport and carbon dioxide compression (∼3%) if renewable energy sources are integrated. From an economic perspective, the penalty in electricity consumption is fully compensated by the new by-product sales. Taking into account the reduction of electricity sales and current prices of trona and sodium bicarbonate a return of investment is obtained in the range between 3 and 8.7 years with an internal rate of return over 12%. These values improve the current forecast of any other carbon capture and storage process up to date, which suggests a high interest of the proposed conceptual integration specially for regions where trona is widely available
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