Changes In Phosphate Concentration Research Articles

Influence of mesoscale eddies on the cross-shelf phosphate transport of the Kuroshio Current northeast of Taiwan: A modeling study

The Kuroshio Current flows northeastward along the East China Sea (ECS) shelf break, carrying a large amount of nutrients, and is thus an important source of nutrients for the ECS. The mainstream and transport of the Kuroshio Current are significantly affected by mesoscale eddies. However, the influence of mesoscale eddies on the Kuroshio nutrient input into the ECS is unknown. We add constructed cyclonic and anticyclonic eddies to a hydrodynamic model to explore the influence of mesoscale eddies on cross-shelf Kuroshio phosphate input into the ECS. This model suitably reproduces the fate of mesoscale eddies and the variation in the Kuroshio Current during eddy-current interactions. The simulation results reveal that during the strong interaction between the Kuroshio Current and mesoscale eddy east of Taiwan, the cyclonic eddy reduces the on-shelf phosphate flux, while the anticyclonic eddy increases the Kuroshio phosphate input to the ECS. When the anticyclonic eddy moves to the Okinawa Trough, it reduces the Kuroshio phosphate input into the ECS.These basic features are not sensitive to the initial latitude of the eddy center east of Taiwan. The change in cross-shelf phosphate flux is caused by the changes in cross-shelf velocity and phosphate concentration along the shelf. Momentum balance analyses suggest that the change in cross-shelf velocity is mainly caused by the change in the pressure gradient term due to eddy-induced changes in sea surface height in the horizontal direction and isotherm tilting in the vertical direction. The advection-diffusion equation analysis shows that the change in phosphate concentration along the shelf is attributed to changes in the upper horizontal advection and lower vertical advection of phosphate, which are induced by the upper phosphate change and vertical velocity change along the shelf, respectively. This study has important implications for the possible response of the ECS ecosystem to mesoscale eddies that are partly triggered by enhanced typhoons east of Taiwan under global warming.

Interaction between inorganic phosphate concentration and glucose metabolism in mild refeeding syndrome model.

Refeeding syndrome is a major clinical problem that leads to fatal complications in patients suffering from malnutrition. Hypophosphatemia inevitably is observed at the onset of refeeding syndrome and therefore is monitored during refeeding; however, the causes of metabolic changes in phosphate concentration during refeeding remain poorly understood. In a previous study, we established a refeeding syndrome model employing total parenteral nutrition with insulin-induced hypophosphatemia, but the symptoms were severe and the metabolic mechanisms in this model may not have been representative of clinical conditions. Therefore, we established a new animal model of mild refeeding syndrome by using a shorter fasting period followed by a single refeeding. These mild refeeding syndrome-model rats exhibited hypophosphatemia without increases in urinary phosphate excretion. Interestingly, administration of the combination of phosphate and insulin during refeeding promoted insulin secretion during refeeding. This model implies that Pi may directly promote insulin secretion in pancreatic cells. These results clarify the interaction between phosphate and glucose metabolism pancreatic cells during refeeding syndrome in a mild refeeding syndrome model.

Glendonite concretion formation due to dead organism decomposition

Glendonite is generally accepted as a calcite pseudomorph after ikaite (CaCO3·6H2O) and is commonly preserved in spherical carbonate concretions known as glendonite concretions in marine sedimentary rocks. Although they have widely attracted attention as environmental indicators, the detailed geochemical process underlying glendonite formation is not fully understood. Here to show the glendonite concretion formation process, we conducted detailed macro- and microscopic observations, carbon and oxygen isotopic analyses (δ13C and δ18O), chemical composition analyses, and elemental mapping of glendonite concretions from four Cenozoic marine sedimentary strata in Japan. The occurrence of glendonite and concretions around dead organisms such as bivalves, ghost shrimp, or soft-bodied organisms forming ichnofossils, and the negative δ13C values of glendonite concretions around −20‰ to −10‰ showed that organic matter in dead organisms served as a carbon source for both ikaite crystals and the surrounding concretions. Highly concentrated phosphorus and its distribution patterns in glendonite concretions showed that changes of phosphate concentration in porewater play a crucial role in the sequential formation process from ikaite crystallization to syngenetically surrounding calcite concretion growth. The sequential processes of glendonite concretion formation progressed rapidly owing to the supply of bicarbonate during the decomposition of organisms in marine sediments. Our work provides a phosphate concentration-controlled growth model of glendonite concretion involving organic decomposition that can be used to evaluate paleoporewater chemical conditions during early diagenesis.

Role of inorganic phosphate concentrations in in vitro activity of fosfomycin

ObjectivesThe objective of this study was to evaluate the in vitro activity of fosfomycin under different physiological concentrations of inorganic phosphate (Pi). MethodsThe wild-type BW25113 strain, four isogenic mutants (ΔglpT, ΔuhpT, ΔglpT-uhpT, and ΔphoB) and six clinical isolates of Escherichia coli with different fosfomycin susceptibilities were used. EUCAST breakpoints were used. Susceptibility was evaluated by agar dilution using standard Mueller–Hinton agar (Pi concentration of 1 mM similar to human plasma concentration) and supplemented with Pi (13 and 42 mM, minimum and maximum urinary Pi concentrations) and/or glucose-6-phosphate (25 mg/L). Fosfomycin transporter promoter activity was assayed using PglpT::gfpmut2 or PuhpT::gfpmut2 promoter fusions in standard Mueller–Hinton Broth (MHB), supplemented with Pi (13 or 42 mM) ± glucose-6-phosphate. Fosfomycin activity was quantified, estimating fosfomycin EC50 under different Pi concentrations (1, 13 and 42 mM + glucose-6-phosphate) and in time–kill assays using fosfomycin concentrations of 307 (maximum plasma concentration (Cmax)), 1053 and 4415 mg/L (urine Cmax range), using MHB with 28 mM Pi (mean urine Pi concentration) + 25 mg/L glucose-6-phosphate. ResultsAll the strains showed decreased susceptibility to fosfomycin linked to increased Pi concentrations: 1–4 log2 dilution differences from 1 to 13 mM, and 1–8 log2 dilution differences at 42 mM Pi. Changes in phosphate concentration did not affect the expression of fosfomycin transporters. By increasing Pi concentrations higher fosfomycin EC50 bacterial viability was observed, except against ΔglpT-uhpT. The increase in Pi reduced the bactericidal effect of fosfomycin. DiscussionPi variations in physiological fluids may reduce fosfomycin activity against E. coli. Elevated Pi concentrations in urine may explain oral fosfomycin failure in non-wild-type but fosfomycin-susceptible E. coli strains.

Oxidative ATP synthesis in human quadriceps declines during 4minutes of maximal contractions.

During maximal exercise, skeletal muscle metabolism and oxygen consumption remain elevated despite precipitous declines in power. Presently, it is unclear whether these responses are caused by an increased ATP cost of force generation (ATPCOST ) or mitochondrial uncoupling; a process that reduces the efficiency of oxidative ATP synthesis (ATPOX ). To address this gap, we used 31-phosphorus magnetic resonance spectroscopy to measure changes in ATPCOST and ATPOX in human quadriceps during repeated trials of maximal intensity knee extensions lasting up to 4min. ATPCOST remained unchanged. In contrast, ATPOX plateaued by ∼2min and then declined (∼15%) over the final 2min. The maximal capacity for ATPOX (Vmax ), as well as ADP-specific rates of ATPOX , were also significantly diminished. Collectively, these results suggest that mitochondrial uncoupling, and not increased ATPCOST , is responsible for altering the regulation of skeletal muscle metabolism and oxygen consumption during maximal exercise. The relationship between skeletal muscle oxygen consumption and power output is augmented during exercise at workloads above the lactate threshold. Potential mechanisms for this response have been hypothesized, including increased ATP cost of force generation (ATPCOST ) and mitochondrial uncoupling, a process that reduces the efficiency of oxidative ATP synthesis (ATPOX ). To test these hypotheses, we used phosphorus magnetic resonance spectroscopy to non-invasively measure changes in phosphate concentrations and pH in the vastus lateralis muscle of nine young adults during repeated trials of maximal, all-out dynamic knee extensions (120°s-1 , 1 every 2s) lasting 24, 60, 120, and 240s. ATPOX was measured at each time point from the initial velocity of PCr resynthesis, and ATPCOST was calculated as the sum of ATP synthesized by the creatine and adenylate kinase reactions, non-oxidative glycolysis, ATPOX and net changes in [ATP]. Power output declined in a reproducible manner for all four trials. ATPCOST did not change over time (main effect P=0.45). ATPOX plateaued from 60 to 120s and then decreased over the final 120s (main effect P=0.001). The maximal capacity for oxidative ATP synthesis (Vmax ), as well as ADP-specific rates of ATPOX , also decreased over time (main effect P=0.001, both). Collectively, these results demonstrate that prolonged maximal contraction protocols impair oxidative energetics and implicate mitochondrial uncoupling as the mechanism for this response. The causes of mitochondrial uncoupling are presently unknown but may offer a potential explanation for the dissociation between skeletal muscle power output and oxygen consumption during maximal, all-out exercise protocols.

In vitro measurement of the chemical changes occurring within β-tricalcium phosphate bone graft substitutes

Several mechanisms proposed to explain the osteoinductive potential of calcium phosphates involve surface mineralization (“bioactivity”) and mention the occurrence of concentration gradients between the inner and the outer part of the implanted material. Determining the evolution of the local chemical environment occurring inside the pores of an implanted bone graft substitute (BGS) is therefore highly relevant. A quantitative and fast method was developed to measure the chemical changes occurring within the pores of β-Tricalcium Phosphate (β-TCP) granules incubated in a simulated body fluid. A factorial design of experiment was used to test the effect of particle size, specific surface area, microporosity, and purity of the β-TCP granules. Large pH, calcium and phosphate concentration changes were observed inside the BGS and lasted for several days. The kinetics and magnitude of these changes (up to 2 pH units) largely depended on the processing and properties of the granules. Interestingly, processing parameters that increased the kinetics and magnitude of the local chemical changes are parameters considered to favor calcium phosphate osteoinduction, suggesting that the model might be useful to predict the osteoinductive potential of BGSs. Statement of significanceRecent results suggest that in situ mineralization of biomaterials (polymers, ceramics, metals) might be key in their ability to trigger ectopic bone formation. This is the reason why the effect on in situ mineralization of various synthesis parameters of β-tricalcium phosphate granules was studied (size, microporosity, specific surface area, and Ca/P molar ratio). To the best of our knowledge, this is the first article devoted to the chemical changes occurring within the pores of a bone graft substitute. We believe that the manuscript will prove to be highly important in the design and mechanistic understanding of drug-free osteoinductive biomaterials.

Investigation of possible high-energy phosphate concentration changes in the visual cortex for different stimulus frequencies

Purpose Many works have reported changes in the visual cortex regarding stimulation with different flickering frequencies using various neuroimaging techniques. Also, many phosphorus functional magnetic resonance spectroscopy (31P-fMRS) studies have reported high-energy phosphate (HEP) changes in the visual cortex during visual stimulation at 8 Hz, compared with rest periods. However, there have been no studies attempting to measure HEP changes during visual stimulation with different flickering frequencies. The aim of this work was to use the 31P-fMRS technique to assess possible HEP changes during visual stimulation experiments with stimuli flickering at 4 Hz or 8 Hz, and compare the results obtained with the different frequencies.

In Vitro Measurement of the Chemical Changes Occurring within Β-Tricalcium Phosphate Bone Graft Substitutes

Several mechanisms proposed to explain the osteoinductive potential of calcium phosphates involve surface mineralization (bioactivity) and mention the occurrence of concentration gradients between the inner and the outer part of the implanted material. Determining the evolution of the local chemical environment occurring inside the pores of an implanted bone graft substitute (BGS) is therefore highly relevant. A quantitative and fast method was developed to measure the chemical changes occurring within the pores of β-Tricalcium Phosphate (β-TCP) granules incubated in a simulated body fluid. A factorial design of experiment was used to test the effect of particle size, specific surface area, microporosity, and purity of the β-TCP granules. Large pH, calcium and phosphate concentration changes were observed inside the BGS and lasted for several days. The kinetics and magnitude of these changes (up to 2 pH units) largely depended on the processing and properties of the granules. Interestingly, processing parameters that increased the kinetics and magnitude of the local chemical changes are parameters considered to favor calcium phosphate osteoinduction, suggesting that the model might be useful to predict the osteoinductive potential of BGSs.

Application of geostatistical methods for mapping groundwater phosphate construction in Eyvan plain, Ilam Province, Iran

The purpose of this study was to evaluate the spatial changes of groundwater phosphate concentrations using geostatistical methods based on data from 10 groundwater wells. One of the conventional tools in decision making on the groundwater management is geostatistical method. To evaluate the spatial changes of phosphate concentrations in groundwater, the universal kriging method with cross-validation was used for mapping and estimating groundwater phosphate concentrations in Eyvan Plain, Iran. Phosphate concentration followed a log-normal distribution and demonstrated a moderate spatial dependence according to the nugget ratio (60%). The experimental variogram of groundwater phosphate concentration was best-fitted by a spherical model. Cross-validation errors were within an acceptable level. According to the spatial distribution map, phosphate pollution in the groundwater occurred mostly in the west of the plain because of the phosphate discharge from the industrial effluents.

Phosphate dynamics in the drinking water catchment area of the Dobromierz Reservoir

AbstractSurface waters polluted by nutrients from agricultural sources or sewage can change their trophic state into high productive and rich in nutrient content. In particular, phosphates are often regarded as the main hazard because they may activate eutrophication. This article presents the studies conducted in order to understand better the process of phosphate build-up in surface waters of Strzegomka River at the inflow and outflow from Dobromierz Reservoir, Lower Silesia, Poland, Central Europe. The Dobromierz Reservoir is the source of drinking water for over 25,000 people. Daily changes in phosphate concentrations were analysed during the hydrological year XI 2000–X 2001 and in the long-term monthly changes over the period of 15 years (2000–2014). Phosphate concentrations monitored in Strzegomka River showed great changeability. Peak phosphate concentrations reaching 1.70 mg /L were noted in the catchment in the autumn of the hydrological year 2000/2001. The mean concentration of phosphates on the...

Denitrification and flushing of the Santa Barbara Basin bottom waters

The sediments of the Santa Barbara Basin (SBB) are an important paleoecological resource since their structure reflects the oxygenation of the bottom waters and the quality and quantity of the particulate matter which is sequestered to the bottom of the basin. These properties are controlled by regional atmospheric and oceanic climate. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) program has been monitoring the bottom waters of the SBB on a regular basis since 1986. Over the last decade, properties of SBB bottom waters have undergone dramatic changes: low concentrations of nitrate were observed more frequently and concentrations of nitrite, at times, reached values of 7µM, in contrast to maximum concentrations of 0.2µM observed during the earlier time period. Here we study the links between regional climate and conditions at the bottom of the SBB by relating recent changes in bottom water chemistry to local and regional forcing of the basin. Varying rates of primary production of the overlying water or rates of export production were not significantly related to the observed biogeochemical changes in the basin. Rather, the frequency or rate of flushing, as inferred from phosphate concentration changes at the bottom of the basin, and decreasing concentrations of oxygen in the waters outside the basins could be related to the observed changes. The episodic more than 10-fold increases of nitrite in the bottom waters likely represent a tipping point in the biogeochemical system driven by decreasing concentrations of oxygen in the bottom waters.

Calcification in the planktonic foraminifera <i>Globigerina bulloides</i> linked to phosphate concentrations in surface waters of the North Atlantic Ocean

Abstract. Marine calcifiers, such as planktonic foraminifera, form a major component of the global carbon cycle, acting as both a source and sink of CO2. Understanding factors that affect calcification in these organisms is therefore critical in predicting how the oceans will respond to increased CO2 concentrations in the atmosphere. Here, size-normalised weights (SNWs) of the planktonic foraminifera Globigerina bulloides, collected from the surface waters of the North Atlantic Ocean, are compared with in situ carbonate ion concentrations ([CO32–]), sea-surface temperature, optimum growth conditions and nutrient concentrations. Changes in phosphate concentrations ([PO43–], range: 0.04–0.39 μM) explained the majority of G. bulloides SNW variation, with reduced test masses at higher concentrations. Two factors already known to influence calcification in foraminifers, [CO32–] and temperature, were also positively correlated over the range of values examined (148–181 μM kg−1 and 10.3–12.7 °C respectively). No evidence was found for increased SNWs under apparent optimum growth conditions, indicated by G. bulloides abundances. However, "growth potentials" (μ), derived from modelled growth rates (d–1), were positively correlated with SNWs, suggesting that this may be a better proxy for optimum growth conditions. These findings point to the potential importance of [PO43–] in determining calcification intensities in foraminifera, a factor which has been overlooked by previous studies on these organisms. The confirmation of this via carefully controlled culture studies is recommended in the future.

Regulation of the dissolved phosphate concentration of a mountainous stream, Kitakyushu, Southwestern Japan

The phosphate concentration in mountainous stream water can be a measure of the forest condition, because its concentration will be low when the biomass in the forest is increasing and vice versa when the forest is declining. To investigate the seasonal change in the dissolved phosphate concentration of the mountainous stream water of the Yamakami River, Kitakyushu, from June 2009 to August 2010, and the regulation mechanism of the phosphate concentration, solid-phase spectrophotometry, which can be applicable to natural water without any pretreatment procedures, was employed for the determination of phosphate at μg P L(-1) levels in natural water. The phosphate concentrations in the mountainous stream waters at 6 sites ranged from 2.2 to 13 μg P L(-1), and those from the catchment area of the steady state forest were 5.3 ± 1.6 (±1 SD) μg P L(-1). Changes in the concentration were fairly small even during a storm runoff. The average phosphate concentration of rain was 2.8 ± 0.7 μg P L(-1), about half of the concentration in the stream water. The rate of runoff in forest areas is generally considered to be about 50% of the total precipitation. For a forest under a climax condition, the phosphate concentration is estimated to be regulated by the fallout and evapotranspiration (α = 0.05). At one of the sites, an upstream tributary, where a fairly big landslide occurred before July in 2009, the phosphate concentration was the highest, suggesting that the biomass may still be decreasing. For all of the six sites examined, a characteristic seasonal change in phosphate concentration was observed, reflecting the local budget between the biological decomposition of plant matter and the consumption by the biomass. The increase in the phosphate concentration during late spring and early summer may result from the extensive decomposition of plant litter mainly supplied in autumn and of plant matter relating to spring blooming such as fallen flowers, pollen and immature fruits. The proposed method using the phosphate concentration in surface stream waters without the period of the seasonal change mentioned above is expected to be very helpful in diagnosing the condition of forests.

Mice Lacking the Sodium-Dependent Phosphate Import Protein, Pit-1, Have a Severe Defect in Terminal Erythroid Differentiation

Abstract 681Phosphate is the second most abundant mineral in the human body and plays an essential role in phospholipids, nucleoproteins and nucleic acids, bone mineralization, the storage and liberation of metabolic energy, and enzyme activity. While our understanding of the mechanisms of phosphate homeostasis has advanced, little is known about how the body initially senses changes in phosphate concentration or the downstream biological processes regulated by these concentration changes. Among the three families of membrane mammalian sodium-phosphate import proteins, PiT-1 and its family member, PiT-2, have the highest substrate affinity. PiT-1 is broadly expressed (Proc Nat Acad Sci, 91,7071-75;1994). Cell line models suggest PiT-1 functions in cellular phosphate homeostasis and vascular calcification (PLoS One, 5,e9148;2010). To determine its in vivo role, two groups have generated PiT-1-null mice. Constitutive deletion of PiT-1 results in embryonic lethality at midgestation and mutant embryos display pale livers (the site of fetal erythropoiesis) with increased apoptosis and reduced hematopoietic colony growth (PLoS One, 5, e9148:2010 & Genesis, 47,858-863;2009). These findings suggest that PiT-1 is required for normal erythropoiesis or hematopoiesis, and provided the rationale to characterize the hematopoietic phenotype of post-natal mice lacking PiT-1. We have discovered that mice lacking PiT-1 have markedly abnormal erythropoiesis which models low-grade myeodysplastic syndromes(MDS). MDS comprise a varied group of malignant stem cell disorders characterized by ineffective blood cell production resulting in increased apoptosis and dysplasia in bone marrow progenitor cells and peripheral blood cytopenias. The precise molecular basis of MDS remains unknown and its wide phenotype likely reflects multiple pathophysiologies. We bred mice expressing a conditional PiT-1 allele (PiT-1flox, gift from the Giachelli Lab) to mice expressing the Mx-Cre transgene to generate a viable null mouse for study. PiT-1-deleted mice develop a severe hypoproliferative, macrocytic anemia (HGB 4.5g/dL±0.3 vs. 13.3±1.0, p<1.0E10−4, MCV 53.1fL±0.9 vs. 49.1±0.6, p=4.6E−3, deleted n=9, control n=7, mean±SEM, Student’s t-test) with elevated erythropoietin levels (33,300pg/mL±1300 vs. 650±210, deleted n=7, control n=6, p<1.0E10−4). Their spleens (a site of stress erythropoiesis in mice) are markedly enlarged (spleen weight in mg/body weight in g: 44.1±4.0 vs. 4.8±0.6, deleted n=4, control n=4, p<1.0E10−4) due to a dramatic expansion of erythroid precursors. Bone marrow cytospins and sternal sections from PiT-1-deleted mice demonstrate erythroid hyperplasia, maturation arrest, and morphologic dyserythropoiesis. Flow cytometric analyses of marrow performed to quantitatively define the terminal stages of erythroid differentiation demonstrate a relative expansion of proerythroblasts and basophilic erythroblasts in deleted mice with increased apoptosis (annexinV+7AAD−/7AAD− cells: 17.9%±2.7 vs. 8.0±0.4, p=0.02, deleted n=3, control n=3) compared to control mice; splenic analyses show similar findings. We confirmed that the defect in erythroid differentiation in PiT-1-deleted mice is intrinsic to the hematopoietic system by hematopoietic colony assays and by demonstrating anemia in lethally irradiated mice transplanted with PiT-1flox/flox;Mx-cre marrow and then treated with poly(I)poly(C) to delete PiT-1 specifically in engrafted cells (HGB deleted 4.3 g/dl±1.0, n=5 vs. control 13.9±0.4, n=6, 7–9 weeks post-deletion, p < 1.0E10−4). Cell cycle analyses of Ter119+-erythroid cells reveal an expanded S-phase fraction in PiT-1-deleted cells compared to controls, which can be accounted for by the expanded proerythroblast and basophilic erythroblast populations in mice lacking PiT-1. Ongoing studies are aimed at determining how a lack of PiT-1 results in ineffective erythropoiesis and severe anemia. Our work may lend insight into the pathways linking erythroid differentiation with proliferation and potentially to cellular respiration. These are pathways implicated in the pathogenesis of myelodysplastic syndromes. This work may also contribute to the emerging and novel hypothesis that phosphate acts as a signaling molecule, which modulates cell proliferation via PiT-1 (J Bio Chem 284,31363-74,2009) potentially in a tissue-specific manner. Disclosures:No relevant conflicts of interest to declare.

Bioassisted capture and release of nanoparticles on nanolithographed ZnO films

Using an artificial peptide library, we have identified a peptide that has strict selectiveaffinity for ZnO surfaces. The binding affinity of the peptide on the ZnO surface can becontrolled simply through changes in phosphate concentration at constant pH andtemperature. In this study, we functionalized inorganic nanoparticles by orderlyconjugating ZnO-binding peptides (ZnOBPs) on the surface of cadmium selenide(CdSe) nanoparticles and performed spontaneous and reversible nanopatterning ofZnOBP-displayed nanoparticles on lithographed ZnO films. Conjugation of ZnOBPs onCdSe nanoparticles caused spontaneous adsorption of the nanoparticles on a ZnO film, andfluorescence and cathodoluminescence images clearly showed specific adsorption ofnanoparticles on the ZnO films lithographed on nano- and micrometer scales. Theselectively bound nanoparticles on ZnO films were completely released by changing thephosphate concentration in solution; such release did not require heat or mechanicalapplications. Repeated capture and release of nanoparticles were achieved on themicrometer scale. Our results show the potential of material-binding peptides fornanopatterning and dynamic microarrays.

Chemistry misconceptions associated with understanding calcium and phosphate homeostasis

Successful learning of many aspects in physiology depends on a meaningful understanding of fundamental chemistry concepts. Two conceptual diagnostic questions measured student understanding of the chemical equilibrium underlying calcium and phosphate homeostasis. One question assessed the ability to predict the change in phosphate concentration when calcium ions were added to a saturated calcium phosphate solution. Fifty-two percent of the students correctly predicted that the phosphate concentration would decrease in accord with the common ion effect. Forty-two percent of the students predicted that the phosphate concentration would not change. Written explanations showed that most students failed to evoke the idea of competing chemical equilibria. A second question assessed the predicted change in calcium concentration after solid calcium phosphate was added to a saturated solution. Only 11% of the students correctly predicted no change in calcium concentration; 86% of the students predicted an increase, and many based their prediction on a mistaken application of Le Chatelier's principle to heterogeneous equilibria. These results indicate that many students possess misconceptions about chemical equilibrium that may hamper understanding of the processes of calcium and phosphate homeostasis. Instructors can help students gain greater understanding of these physiochemical phenomena by adopting strategies that enable students achieve more accurate conceptions of chemical equilibria.

FACT and the Proteasome Promote Promoter Chromatin Disassembly and Transcriptional Initiation

The packaging of the eukaryotic genome into chromatin represses gene expression by blocking access of the general transcription machinery to the underlying DNA sequences. Accordingly, eukaryotes have developed a variety of mechanisms to disrupt, alter, or disassemble nucleosomes from promoter regions and open reading frames to allow transcription to occur. Although we know that chromatin disassembly from the yeast PHO5 promoter is triggered by the Pho4 activator, the mechanism is far from clear. Here we show that the Pho4 activator can occupy its nucleosome-bound DNA binding site within the PHO5 promoter. In contrast to the role of Saccharomyces cerevisiae FACT (facilitates chromatin transcription) complex in assembling chromatin within open reading frames, we find that FACT is involved in the disassembly of histones H2A/H2B from the PHO5 promoter during transcriptional induction. We have also discovered that the proteasome is required for efficient chromatin disassembly and transcriptional induction from the PHO5 promoter. Mutants of the degradation function of the proteasome have a defect in recruitment of the Pho4 activator, whereas mutants of the ATPase cap of the proteasome do recruit Pho4 but are still delayed for chromatin assembly. Finally, we rule out the possibility that the proteasome or ATPase cap is driving chromatin disassembly via a potential ATP-dependent chromatin remodeling activity.

Novel Mechanisms in the Regulation of Phosphorus Homeostasis

Phosphorus plays a critical role in diverse biological processes, and, therefore, the regulation of phosphorus balance and homeostasis are critical to the well being of the organism. Changes in environmental, dietary, and serum concentrations of inorganic phosphorus are detected by sensors that elicit changes in cellular function and alter the efficiency by which phosphorus is conserved. Short-term, post-cibal responses that occur independently of hormones previously thought to be important in phosphorus homeostasis may play a larger role than previously appreciated in the regulation of phosphorus homeostasis. Several hormones and regulatory factors such as the vitamin D endocrine system, parathyroid hormone, and the phosphatonins (FGF-23, sFRP-4, MEPE) among others, may play a role only in the long-term regulation of phosphorus homeostasis. In this review, we discuss how organisms sense changes in phosphate concentrations and how changes in hormonal factors result in the conservation or excretion of phosphorus.

The effect of a 10% carbamide peroxide bleaching agent on the phosphate concentration of tooth enamel assessed by Raman spectroscopy

The study assessed changes in phosphate concentrations of surface enamel treated with a proprietary bleaching agent ('PEROXIDE') containing 10% carbamide peroxide over a 28-day period using Raman spectroscopy. Six non-carious human molar teeth (age range 12-21 years), extracted for orthodontic reasons, were used. From the enamel face of each half tooth, a near flat enamel section, approximately 2 x 2 mm, was cut, providing 12 specimens. Each specimen was treated with 10% carbamide peroxide for 8 h day(-1) for 28 consecutive days, with Raman spectra being obtained prior to bleaching and after 7, 14, 21 and 28 days. Raman spectra were acquired on a confocal LabRam 300 spectrometer fitted with an Olympus B microscope (Olympus, Middlesex, UK). The difference in the maximum peak values for phosphate group concentrations were tested using the Friedman test (non-parametric anova) and Dunn's multiple comparison test. An intense broad band at 980 cm(-1), characteristic of phosphate groupings, was always observed. At 7 and 14 days, and again at 28 days, there was a significant decrease in the phosphate group concentration compared with base-line measurements (P < 0.05) but not at 21 days (P > 0.05). Ideally, bleaching should not be continued to a point where surface enamel is lost, and the present study suggests that a regime using 10% carbamide peroxide should not extend to 7 days.

Relationship between the electric conductivity and phosphorus concentration variations in an enhanced biological nutrient removal process

Phosphorus release and uptake in a sequencing batch reactor were monitored by the simple online measurements of electric conductivity (EC) and oxidation-reduction potential (ORP), and the result was verified by the measurement of phosphate concentration changes. The influence of nitrate ion presence on the phosphorus removal was evaluated by a jar test operated in the cyclic anaerobic (anoxic)-aerobic condition. The relationships of EC, ORP and metal species with phosphorus concentrations were investigated. Under strict anaerobic conditions, EC showed positive correlation with phosphorus concentrations, but it became negligible under anoxic conditions with nitrate present. Strong inverse correlation was found between ORP values and phosphorus concentration. The increase and decrease of magnesium and potassium ions took place in accordance with phosphorus release and uptake, and the relationship between the metal species and phosphorus changes was clearer in the anaerobic condition than anoxic condition.