512 research outputs found
Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility
Atmospheric deposition is one of the main sources of dissolved iron (Fe) in
the ocean surfaces. Atmospheric processes are recognized as controlling
fractional Fe solubility (Fesol%) in marine aerosol particles.
However, the impact of these processes on Fesol% remains unclear.
One of the reasons for this is the lack of field observations focusing on
the relationship between Fesol% and Fe species in marine aerosol
particles. In particular, the effects of organic ligands on Fesol%
have not been thoroughly investigated in observational studies. In this
study, Fe species in size-fractionated aerosol particles in the Pacific
Ocean were determined using X-ray absorption fine structure (XAFS)
spectroscopy. The internal mixing states of Fe and organic carbon were
investigated using scanning transmission X-ray microscopy (STXM). The
effects of atmospheric processes on Fesol% in marine aerosol
particles were investigated based on the speciation results. Iron in
size-fractionated aerosol particles was mainly derived from mineral dust,
regardless of aerosol diameter, because the enrichment factor of Fe was
almost 1 in both coarse (PM>1.3) and fine aerosol particles
(PM1.3). Approximately 80 % of the total Fe (insoluble + labile
Fe) was present in PM>1.3, whereas labile Fe was mainly present in
PM1.3. The Fesol% in PM>1.3 was not significantly
increased (2.56±2.53 %, 0.00 %–8.50 %, n=20) by the
atmospheric processes because mineral dust was not acidified beyond the
buffer capacity of calcite. In contrast, mineral dust in PM1.3 was
acidified beyond the buffer capacity of calcite. As a result, Fesol%
in PM1.3 (0.202 %–64.7 %, n=10) was an order of magnitude higher
than that in PM>1.3. The PM1.3 contained ferric organic complexes
with humic-like substances (Fe(III)-HULIS, but not Fe-oxalate complexes),
and the abundance correlated with Fesol%. Iron(III)-HULIS was formed
during transport in the Pacific Ocean because Fe(III)-HULIS was not found in
aerosol particles in Beijing and Japan. The pH estimations of mineral dust
in PM1.3 established that Fe was solubilized by proton-promoted
dissolution under highly acidic conditions (pH < 3.0), whereas
Fe(III)-HULIS was stabilized under moderately acidic conditions (pH 3.0–6.0). Since the observed labile Fe concentration could not be
reproduced by proton-promoted dissolution under moderately acidic
conditions, the pH of mineral dust increased after proton-promoted
dissolution. The cloud process in the marine atmosphere increases the
mineral dust pH because the dust particles are covered with organic carbon
and Na. The precipitation of ferrihydrite was suppressed by Fe(III)-HULIS
owing to its high water solubility. Thus, the organic complexation of Fe
with HULIS plays a significant role in the stabilization of Fe that was
initially solubilized by proton-promoted dissolution.</p
Cryo-EM structure of a functional monomeric Photosystem I from Thermosynechococcus elongatus reveals red chlorophyll cluster
A high-resolution structure of trimeric cyanobacterial Photosystem I (PSI) from Thermosynechococcus elongatus was reported as the first atomic model of PSI almost 20 years ago. However, the monomeric PSI structure has not yet been reported despite long-standing interest in its structure and extensive spectroscopic characterization of the loss of red chlorophylls upon monomerization. Here, we describe the structure of monomeric PSI from Thermosynechococcus elongatus BP-1. Comparison with the trimer structure gave detailed insights into monomerization-induced changes in both the central trimerization domain and the peripheral regions of the complex. Monomerization-induced loss of red chlorophylls is assigned to a cluster of chlorophylls adjacent to PsaX. Based on our findings, we propose a role of PsaX in the stabilization of red chlorophylls and that lipids of the surrounding membrane present a major source of thermal energy for uphill excitation energy transfer from red chlorophylls to P700
A Theory of Anisotropic Semiconductor of Heavy Fermions
It is demonstrated that a {\veck}-dependence of the hybridization matrix
element between - and conduction electrons can give rise to an anisotropic
hybridization gap of heavy fermions if the filling of electrons corresponds to
that of the band insulator. The most interesting case occurs when the
hybridization vanishes along some symmetry axis of the crystal reflecting a
particular symmetry of the crystal field. The results of a model calculation
are consistent with wide range of anomalous properties observed in CeNiSn and
its isostructural compounds, the anisotropic semiconductor of heavy fermions.
In particular, highly sensitive effect of impurity scattering on the residual
density of states for zero energy excitation and the anisotropic temperature
dependence of the resistivity are well explained. It is also discussed that a
weak semimetallic behavior arises through the weak \veck-dependence of the
-electron self-energy \Sigma_{f}(\veck,0).Comment: 21 pages, LaTeX (JPSJ style file) and 13 postscript figures, To
appear in J. Phys. Soc. Jp
Measurement report: Stoichiometry of dissolved iron and aluminum as an indicator of the factors controlling the fractional solubility of aerosol iron – results of the annual observations of size-fractionated aerosol particles in Japan
The atmospheric deposition of iron (Fe) promotes primary production in the
surface ocean, which results in the enhanced uptake of carbon dioxide into
surface seawater. Given that microorganisms in seawater utilize dissolved Fe
(d-Fe) as a nutrient, the bioavailability of Fe in aerosol particles depends
on its solubility. However, the factors controlling fractional Fe solubility
(Fesol %) in aerosol particles have not been fully understood. This
study performed annual observations of the total and dissolved metal
concentrations in size-fractionated (seven fractions) aerosol particles at
Higashi-Hiroshima, Japan. The feasibility of the molar concentration ratio
of d-Fe relative to dissolved Al ([d-Fe] / [d-Al]) as an indicator of sources
of d-Fe in aerosol particles was investigated because this ratio is likely
dependent on the emission sources of Fe (e.g., mineral dust, fly ash, and
anthropogenic Fe oxides) and their dissolution processes (proton- and
ligand-promoted dissolutions). Approximately 70 % of the total Fe in
total suspended particulates (TSPs) was present in coarse aerosol particles,
whereas about 70 % of d-Fe in TSPs was mainly found in fine aerosol
particles. The average Fesol % in fine aerosol particles (11.4 ± 7.0 %) was higher than that of coarse aerosol particles (2.19 ± 2.27 %). In addition, the average ratio of [d-Fe] / [d-Al] in coarse
aerosol particles (0.408 ± 0.168) was lower than that in fine aerosol
particles (1.15 ± 0.80). The range of [d-Fe] / [d-Al] ratios in the
coarse aerosol particles (0.121–0.927) was similar to that obtained by
proton-promoted dissolution of mineral dust (0.1–1.0), which indicates that
the d-Fe in coarse aerosol particles was derived from mineral dust. The
[d-Fe] / [d-Al] ratios of fine aerosol particles ranged from 0.386 to 4.67,
and [d-Fe] / [d-Al] ratios greater than 1.50 cannot be explained by proton-
and ligand-promoted dissolutions (1.00 < [d-Fe] / [d-Al] < 1.50). The [d-Fe] / [d-Al] ratio correlated with the enrichment factor of Fe
in fine aerosol particles (r: 0.505), which indicates that anthropogenic Fe
with a high [d-Fe] / [d-Al] ratio was the source of d-Fe in fine aerosol
particles. The high [d-Fe] / [d-Al] ratio was attributed to anthropogenic Fe
oxides emitted from high-temperature combustions. Finally, the fraction of
anthropogenic Fe oxides to d-Fe in TSPs was
calculated based on the [d-Fe] / [d-Al] ratio of aerosols and their emission
source samples. As a result, the fraction of anthropogenic Fe oxides to d-Fe
in TSPs varied from 1.48 % to 80.7 %. A high fraction was observed in
summer when air masses originated from industrial regions in Japan. By
contrast, approximately 10 % of d-Fe in the TSPs collected in
spring and during Asian dust events was derived from anthropogenic Fe oxides
when air masses were frequently transported from East Asia to the Pacific Ocean.
Thus, mineral dust was the dominant source of d-Fe in Asian outflow to the
Pacific Ocean.</p
Electron transport pathways in isolated chromoplasts from Narcissus pseudonarcissus L.
During daffodil flower development, chloroplasts differentiate into photosynthetically inactive chromoplasts having lost functional photosynthetic reaction centers. Chromoplasts exhibit a respiratory activity reducing oxygen to water and generating ATP. Immunoblots revealed the presence of the plastid terminal oxidase (PTOX), the NAD(P)H dehydrogenase (NDH) complex, the cytochrome b(6)f complex, ATP synthase and several isoforms of ferredoxin-NADP(+) oxidoreductase (FNR), and ferredoxin (Fd). Fluorescence spectroscopy allowed the detection of chlorophyll a in the cytochrome b(6)f complex. Here we characterize the electron transport pathway of chromorespiration by using specific inhibitors for the NDH complex, the cytochrome b(6)f complex, FNR and redox-inactive Fd in which the iron was replaced by gallium. Our data suggest an electron flow via two separate pathways, both reducing plastoquinone (PQ) and using PTOX as oxidase. The first oxidizes NADPH via FNR, Fd and cytochrome b(h) of the cytochrome b(6)f complex, and does not result in the pumping of protons across the membrane. In the second, electron transport takes place via the NDH complex using both NADH and NADPH as electron donor. FNR and Fd are not involved in this pathway. The NDH complex is responsible for the generation of the proton gradient. We propose a model for chromorespiration that may also be relevant for the understanding of chlororespiration and for the characterization of the electron input from Fd to the cytochrome b(6)f complex during cyclic electron transport in chloroplasts.Significance Statement Chromorespiration takes place via two pathways, one depends on FNR, ferredoxin, the cytochrome b6f complex, and the other depends on the NDH complex and is ferredoxin independent. We propose an electron transport via the cytochrome b6f complex that involves neither a Q-cycle nor a high potential electron transport chai
Lectin-like bacteriocins from pseudomonas spp. utilise D-rhamnose containing lipopolysaccharide as a cellular receptor
Lectin-like bacteriocins consist of tandem monocot mannose-binding domains and display a genus-specific killing activity. Here we show that pyocin L1, a novel member of this family from Pseudomonas aeruginosa, targets susceptible strains of this species through recognition of the common polysaccharide antigen (CPA) of P. aeruginosa lipopolysaccharide that is predominantly a homopolymer of d-rhamnose. Structural and biophysical analyses show that recognition of CPA occurs through the C-terminal carbohydrate-binding domain of pyocin L1 and that this interaction is a prerequisite for bactericidal activity. Further to this, we show that the previously described lectin-like bacteriocin putidacin L1 shows a similar carbohydrate-binding specificity, indicating that oligosaccharides containing d-rhamnose and not d-mannose, as was previously thought, are the physiologically relevant ligands for this group of bacteriocins. The widespread inclusion of d-rhamnose in the lipopolysaccharide of members of the genus Pseudomonas explains the unusual genus-specific activity of the lectin-like bacteriocins
Takotsubo cardiomyopathy after a dancing session: a case report
<p>Abstract</p> <p>Introduction</p> <p>Stress-induced (Takotsubo) cardiomyopathy is a rare form of cardiomyopathy which presents in a manner similar to that of acute coronary syndrome. This sometimes leads to unnecessary thrombolysis therapy. The pathogenesis of this disease is still poorly understood. We believe that reporting all cases of Takotsubo cardiomyopathy will contribute to a better understanding of this disease. Here, we report a patient who, in the absence of any recent stressful events in her life, developed the disease after a session of dancing.</p> <p>Case presentation</p> <p>A 69-year-old Caucasian woman presented with features suggestive of acute coronary syndrome shortly after a session of dancing. Echocardiography and a coronary angiogram showed typical features of Takotsubo cardiomyopathy and our patient was treated accordingly. Eight weeks later, her condition resolved completely and the results of echocardiography were totally normal.</p> <p>Conclusions</p> <p>Takotsubo cardiomyopathy, though transient, is a rare and serious condition. Although it is commonly precipitated by stressful life events, these are not necessarily present. Our patient was enjoying one of her hobbies (that is, dancing) when she developed the disease. This case has particular interest in medicine, especially for the specialties of cardiology and emergency medicine. We hope that it will add more information to the literature about this rare condition.</p
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