Role Of Phosphate Research Articles

Interpreting the phosphocreatine time constant in aerobically exercising skeletal muscle

to the editor: Francescato et al. ([1][1]) contrast the lack of interindividual correlation between the phosphocreatine (PCr) time constant (τPCr) and the ADP concentration ([ADP]) change from rest to steady state (Δ[ADP]S) during moderate aerobic exercise with the fact that “…ADP

Acid phosphatase and invertase activities of <i>Aspergillus niger</i>

Aspergillus niger is widely used as an enzyme source in industries. Considering its enzymic potential, A. niger was studied for its acid phosphatase (EC 3.1.3.2, orthophosphoric monoester phosphohydrolase), and invertase (EC 3.2.1.26, β-fructofuranoside fructohydrolase) activity in defined media supplemented with 1%, 3%, or 5% sucrose concentrations. Both these enzymes play a key role in phosphate and carbon metabolism in plants, animals, and microorganisms and hence are interesting from the standpoint of biotechnological applications. Ontogenic changes in extracellular, cytoplasmic, and wall-bound enzyme activities of A. niger were studied. Growth in terms of fresh weight showed inverse correlation with pH. At higher pH values, both enzyme activities were higher in the medium supplemented with low sucrose concentration. It was observed that the more the fresh weight of fungi decreased, the greater was the enzyme activity observed. It is suggested that these enzymes may participate in autolysis of fungi and, on the other hand, could prove to be a potential source of industrial application and exploitation.

Response to Comment on “Nitrification in Premise Plumbing: Role of Phosphate, pH, and Pipe Corrosion”. Study Used Conditions That Are Realistic and Representative

Response to Comment on “Nitrification in Premise Plumbing: Role of Phosphate, pH, and Pipe Corrosion”. Study Used Conditions That Are Realistic and Representative

Comment on “Nitrification in Premise Plumbing: Role of Phosphate, pH, and Pipe Corrosion”

Comment on “Nitrification in Premise Plumbing: Role of Phosphate, pH, and Pipe Corrosion”

Nitrification in Premise Plumbing: Role of Phosphate, pH and Pipe Corrosion

Nitrification in PVC premise plumbing is a weak function of pH over the range 6.5--8.5 and is insensitive to phosphate concentrations 5--1000 ppb. Lead pipe enhanced nitrification relative to PVC, consistent with expectations that nitrifiers could benefit from ammonia recycled from nitrate via lead corrosion. Relatively new copper pipe (< 1.5-years-old) did not allow nitrifiers to establish, but nitrifiers gradually colonized over a period of months in brass pipes when copper concentrations were reduced by pH adjustment or orthophosphate. Nitrifiers were inhibited by trace copper, but not by lead levels up to 8000 ppb. In some systems using chloramines, brass in plastic plumbing systems might be more susceptible to lead/copper leaching, and accelerated dezincification, due to lower pH values resulting from nitrification.

The role of phosphate in chronic kidney disease (CKD) progression: Part 2

The role of phosphate in chronic kidney disease (CKD) progression: Part 2

The role of phosphate in chronic kidney disease (CKD) progression: Part 1

The role of phosphate in chronic kidney disease (CKD) progression: Part 1

Arsenic, Cadmium, and Lead in California Cropland Soils: Role of Phosphate and Micronutrient Fertilizers

Phosphate and micronutrient fertilizers contain potentially harmful trace elements, such as arsenic (As), cadmium (Cd), and lead (Pb). We investigated if application of these fertilizer increases the As, Cd, and Pb concentrations of the receiving soils. More than 1000 soil samples were collected in seven major vegetable production regions across California. Benchmark soils (no or low fertilizer input) sampled in 1967 and re-sampled in 2001 served as a baseline. Soils were analyzed for total concentrations of As, Cd, Pb, P, and Zn. The P and Zn concentrations of the soils were indicators of P fertilizer and micronutrient inputs, respectively. Results showed that the concentrations of these elements in the vegetable production fields in some production areas of California had been shifted upward. Principal component analysis and cluster analysis showed that the seven production areas could be sorted into three categories: (i) enrichment of As, Cd, and Pb, which was associated with the enrichment of P and Zn in one of the seven areas surveyed; (ii) enrichment of As, which was associated with enrichment of Zn in two of the seven areas surveyed; and (iii) no remarkable correlation between enrichment of As, Cd, and Pb and enrichment of P and Zn in the other four areas surveyed.

OsPHR2 is involved in phosphate-starvation signaling and excessive phosphate accumulation in shoots of plants.

Previous research has demonstrated that AtPHR1 plays a central role in phosphate (Pi)-starvation signaling in Arabidopsis thaliana. In this work, two OsPHR genes from rice (Oryza sativa) were isolated and designated as OsPHR1 and OsPHR2 based on amino acid sequence homology to AtPHR1. Their functions in Pi signaling in rice were investigated using transgenic plants. Our results showed that both OsPHR1 and OsPHR2 are involved in Pi-starvation signaling pathway by regulation of the expression of Pi-starvation-induced genes, whereas only OsPHR2 overexpression results in the excessive accumulation of Pi in shoots under Pi-sufficient conditions. Under Pi-sufficient conditions, overexpression of OsPHR2 mimics Pi-starvation stress in rice with enhanced root elongation and proliferated root hair growth, suggesting the involvement of OsPHR2 in Pi-dependent root architecture alteration by both systematic and local pathways. In OsPHR2-overexpression plants, some Pi transporters were up-regulated under Pi-sufficient conditions, which correlates with the strongly increased content of Pi. The mechanism behind the OsPHR2 regulated Pi accumulation will provide useful approaches to develop smart plants with high Pi efficiency.

Possible role of the FGF23-Klotho axis in bone mineralization

FGF23 was identified as a causative factor for hypophosphatemic rickets/osteomalacia. The following studies have confirmed its essential role in phosphate and vitamin D metabolism in normal physiology. Recent studies revealed that Klotho, originally identified as an aging-associated molecule, is necessary for the specific action of FGF23. Much attention is now paid to the FGF23-Klotho axis as a novel regulatory system in the mineral metabolism, whereas local action of FGF23 in bone metabolism or bone mineralization remains unresolved.

Fetuin-A, Valve Calcification, and Diabetes

In the current issue of Circulation , Ix et al demonstrate an inverse correlation between mitral and aortic valve calcification and serum fetuin-A levels in a cross-sectional study of 970 patients with coronary artery disease and without renal disease.1 Increased serum fetuin was significantly associated with diabetes mellitus, hypertriglyceridemia, serum albumin, and body mass index, with a weaker association with serum C-reactive protein, low-density lipoprotein cholesterol, and serum calcium. The link between aortic stenosis and fetuin held only in those without diabetes.1 The data highlight the complex interactions of fetuin with inflammation, insulin resistance, and tissue calcification. Furthermore, the results, though intriguing, underscore our lack of understanding of the cellular mechanisms of calcification in diverse pathological substrates, such as the degenerating aortic leaflet and mitral annulus. Article p 2533 Fetuin is a member of the cystatin superfamily of cysteine protease inhibitors, originally discovered as the major component of fetal bovine serum. It is a carrier for growth factors, binds to and inactivates transforming growth factor (TGF)–β and bone morphogenic protein, and is a major component of mineralized bone.2 Fetuin-A is also an acute-phase glycoprotein, produced in adults primarily in the liver, and is a powerful circulating inhibitor of hydroxyapatite formation. Mice that lack fetuin-A exhibit extensive soft-tissue calcification, which is accelerated on a mineral-rich diet, which suggests that fetuin-A acts to inhibit calcification systemically.3 In addition to its effects on mineralization, fetuin-A inhibits insulin receptor autophosphorylation and tyrosine kinase activity in vitro and in vivo. Fetuin-null knockout mice demonstrate improved insulin sensitivity and resistance to diet-induced obesity, and it has been postulated that the absence of fetuin in mice may contribute to the improvement of insulin sensitivity associated with aging.4 Clinically, serum fetuin-A is decreased in patients with moderate to severe chronic kidney disease, especially …

From Chlorella to chloroplasts: a personal note

An historical and personal reflection on the function of the Benson-Calvin Cycle in isolated chloroplasts, the role of inorganic phosphate and the manner in which this might be best presented to students.

Iron deficiency differently affects metabolic responses in soybean roots

Iron deficiency responses were investigated in roots of soybean, a Strategy I plant species. Soybean responds to iron deficiency by decreasing growth, both at the root and shoot level. Chlorotic symptoms in younger leaves were evident after a few days of iron deficiency, with chlorophyll content being dramatically decreased. Moreover, several important differences were found as compared with other species belonging to the same Strategy I. The main differences are (i) a lower capacity to acidify the hydroponic culture medium, that was also reflected by a lower H(+)-ATPase activity as determined in a plasma membrane-enriched fraction isolated from the roots; (ii) a drastically reduced activity of the phosphoenolpyruvate carboxylase enzyme; (iii) a decrease in both cytosolic and vacuolar pHs; (iv) an increase in the vacuolar phosphate concentration, and (v) an increased exudation of organic carbon, particularly citrate, phenolics, and amino acids. Apparently, in soybean roots, some of the responses to iron deficiency, such as the acidification of the rhizosphere and other related processes, do not occur or occur only at a lower degree. These results suggest that the biochemical mechanisms induced by this nutritional disorder are differently regulated in this plant. A possible role of inorganic phosphate in the balance of intracellular pHs is also discussed.

Toxicity of phosphonoformic acid in vascular smooth muscle cells: relationship to vascular calcification

Medial vascular calcification (VC) develops as a consequence of hyperphosphatemia secondary to chronic kidney disease. The role of inorganic phosphate (Pi) transporters in the pathogenesis of VC has been previously determined by interference of RNA and inhibition by phosphonoformic acid (PFA). We have found that inhibition of Pi transport by PFA in vascular smooth muscle cells (VSMC) from rat aorta showed a Ki of 2.6 mM, while the Km for Pi was 0.1 mM. VSMC express both type III Pi transporters, Pit1 and Pit2. When expressed in Xenopus laevis oocytes Pit1 and Pit2 were inhibited with PFA with Ki values of 2.7 and 4.6 mM, respectively, while they showed affinities of 0.1 and 0.2 mM. PFA at either 1 or 5 mM completely prevented calcification of VSMC induced with 2 mM phosphate for 5 days. Phase-contrast microscopy revealed that cells treated with either 1 or 5 mM PFA in either normal (1 mM) or high (2 mM) Pi concentration showed a different morphology and evidence of cell death. Cytotoxicity was analyzed as a function of cytosolic lactate dehydrogenase activity, revealing a mean lethal concentration (LC50) of 0.38 mM. Therefore the prevention calcification was not due to inhibition of Pi transport but to cytotoxicity of PFA that prevented trans-differentiation of VSMC into osteogenic-like cells. Further experiments have been developed to characterize the type of cell death, including apoptosis.

Probing Early Growth Response 1 Interacting Proteins at the Active Promoter in Osteoblast Cells Using Oligoprecipitation and Mass Spectrometry

Current advances in proteomics have allowed for a rapidly expanding integration of associated methodologies with more traditional molecular and biochemical approaches to the study of cell function. Recent studies on the role of inorganic phosphate have suggested this ion is a novel signaling molecule capable of altering the function of numerous cell types. Elevated inorganic phosphate generated in the extracellular microenvironment by differentiating osteoblasts has recently been determined to act through a largely uncharacterized mechanism as an important signaling molecule responsible for altering the transcription of various genes during osteoblast differentiation. The transcription factor, early growth response protein 1 (EGR1), has previously been shown to be involved in the early response of osteoblasts to inorganic phosphate. To elucidate the role of EGR1 as a potential early regulator of transcription in the inorganic phosphate response, an oligoprecipitation procedure was optimized to capture the DNA bound, transcriptionally active form of EGR1. The interacting proteins thusly captured were identified using mass spectrometry (MS). Proteins involved in transcription, RNA processing, and chromatin modification were identified by this approach. The combined oligoprecipitation-MS approach presented here is highly effective for isolating and characterizing entire transcriptional complexes in the DNA bound state and is broadly extendable to the identification of both known and unknown transcription factor protein complexes.

Influence of parathyroid mass on the regulation of PTH secretion

In advanced uremia, parathyroid hormone (PTH) levels should be controlled at a moderately elevated level in order to promote normal bone turnover. As such, a certain degree of parathyroid gland (PG) hyperplasia has to be accepted. No convincing evidence of apoptosis or of involution of PG hyperplasia exists. However, even considerable parathyroid hyperplasia can be controlled when the functional demand for increased PTH levels is abolished. When 20 isogenic PG were implanted into one parathyroidectomized (PTX) rat normalization of Ca(2+) and PTH levels and normal suppressibility of PTH secretion by high Ca(2+) was obtained. Similarly, normal levels of Ca(2+) and PTH and suppressibility of PTH secretion were obtained when Eight isogenic PG from uremic rats were implanted into normal rats or when long-term uremia and severe secondary hyperparathyroidism (sec. HPT) was reversed by an isogenic kidney transplantation. Normalization of PTH levels after experimental kidney transplantation took place despite a persistent decrease of vitamin D receptor (VDR) mRNA and calcium sensing receptor (CaR) mRNA in PG. Thus, in experimental models PTH levels are determined by the functional demand and not by parathyroid mass, per se. When non-suppressible sec. HPT is present in patients referred to PTX, nodular hyperplasia with differences in gene expression between different nodules has been observed in most cases. An altered expression of some autocrine/paracrine factors has been demonstrated in the nodules. Enhanced expression of PTH-related peptide (PTHrP) has been demonstrated in PG from patients with severe secondary HPT. PTHrP has been shown to stimulate PTH secretion in vivo and in vitro. PTH/PTHrP receptor was demonstrated in the parathyroids. The low Ca(2+) stimulated PTH secretion was enhanced by 300% by PTHrP 1-40. The altered quality of the parathyroid mass and not only the increased parathyroid mass, per se, might be responsible for non-controllable hyperparathyroidism in uremia and after kidney transplantation.

Role of inorganic phosphate during electron transfer in the redox system NADH+flavin

We have used 31P NMR and EPR to study the effect of inorganic phosphate (Pi) on the process of electron transfer in oxidation of reduced nicotinamide adenine dinucleotide (NADH) by flavin in aqueous solutions. Observation of a significant (up to 40%) drop in the integrated intensity of the 31P NMR signal for the inorganic phosphate over the course of the reaction is interpreted as a manifestation of the effect of chemically induced polarization of the phosphorus nuclei during singlet-triplet conversion in charge-transfer complexes [NADH…Pi], and is evidence for a possible catalytic role for Pi in processes involving transfer of an electron (hydrogen atom) from NADH to appropriate acceptors. The results presented support the possibility of direct involvement of Pi in a chain of one-electron conversions in chemical systems.

Interactions of doubly phosphorylated human β‐casein with native and reduced, carboxymethylated bovine κ‐casein leading to micelle formation: Role of inorganic phosphate

Milk micelles are largely colloidal complexes of casein (CN) phosphoproteins. The reconstituted micelle system in the absence of inorganic phosphate (Pi) is quite temperature dependent, forming at higher temperatures but disappearing upon cooling. In the present study, β-CN-2P (~30% of the total β-CN) at 3 mg/ml in 0.02 M NaCl, 0.01 M imidazole, pH 7 was mixed with native (N-κ) or reduced, carboxymethylated (RCM-κ) bovine κ-CN at κ/β (w:w) ratios from 1:3 to 1:6. Turbidity (OD400 nm) and a lack of precipitation as temperature (T) increased from 4 to 37°C were used as an index of stability and micelle formation. Analytical ultracentrifuge measurements at different temperatures were also carried out with added Ca+2 and inorganic phosphate (Pi). At 10°C in the absence of Ca+2 and Pi, N-κ plus β-CN-2P (1:3) showed two peaks of ~2 and 4.6 S which became a single peak of ~30S at 37°C. With 2.5 mM Ca+2 and 2 mM Pi, a single peak with ~42S was obtained at 37°C. The S value increased up to 6 mM Pi and then decreased as material precipitated at higher Pi. RCM-κ alone also showed two peaks at 10°C of ~7 and 46S, and at 37°C, two skewed peaks of ~14 and 53S were obtained. For RCM-κ and β-CN-2P at a ratio of 1:6 (w:w),very turbid solutions were seen with increases in Pi. The stabilizing action of RCM-κ was dependent on its concentration. These studies suggest that interactions dictated by the sulfhydryl groups of κ-CN are less important than other interactions.

The role of inorganic phosphate on photosynthesis recovery of common bean after a mild water deficit

A foliar spray of inorganic phosphate (Pi) was applied at the pollination stage of two common bean genotypes A320 and Ouro Negro, growing in pots in a greenhouse. Two days after the foliar Pi supply, a mild water deficit was imposed for 7 days and photosynthesis was evaluated during water stress and recovery. The net CO 2 assimilation rate ( A) and stomatal conductance ( g s) were not affected by Pi supply during the dehydration of either genotype. On the fourth day of water deficit, A320 presented a high value of A despite lower g s, indicating a small effect of g s on A for this genotype, while Ouro Negro showed a low value for both A and g s. However, after rehydration A and g s for A320 and A for Ouro Negro, both supplied with Pi, were higher than for non-Pi-supplied plants. In addition, the O 2 evolution ( A c) of rehydrated A320 with foliar Pi supply was also higher than for non-Pi-supplied plants, and the non-photochemical quenching (NPQ) was higher for rehydrated A320 without foliar Pi. The results revealed an up-regulation of the recovery of photosynthesis after water deficit induced by the foliar Pi supply, which was genotype-specific.

Voltage gating and anions, especially phosphate: A model system

The voltage sensor of voltage gated sodium and potassium channels consists of four sets of transmembrane segments, of which one, called S4, contains at least four arginines; these are presumed to each carry positive charges. The channel opening is usually attributed to the outward (i.e., toward the extracellular side of the membrane) motion of S4. The evidence for this motion is based on certain experiments that appear to show differential access to parts of S4 from the intracellular and extracellular sides of the membrane in the open and closed states. A newly available structure [S.B. Long, E.B. Campbell and R. MacKinnon, Crystal structure of a mammalian voltage-dependent Shaker family K + channel. Science 309 (2005) 897–903; S.B. Long, E.B. Campbell, R. MacKinnon, Voltage sensor of Kv1.2: structural basis of electromechanical coupling. Science 309 (2005) 903–908][1,2] has now been used to argue for a large scale motion, although, as a static structure, it is not conclusive. In this paper, we consider the effect of anions in the surrounding medium. Phosphate is present in the intracellular as well as the extracellular fluid, apparently at hundreds of micromolar concentration, or more. There is evidence in the literature suggesting that phosphate–arginine complexes are rather strong. In a recent calculation one of us [M.E. Green, A possible role for phosphate in complexing the arginines of S4 in voltage gated channels J. Theor. Biol. 233 (2005) 337–341][3] has shown that a model peptide with a 2:1 arg:phosphate complex should have a favorable geometry. Here, we present NMR evidence of the existence of phosphate complexes of a model peptide with two arginines separated by two hydrophobic residues, the same spacing as in S4 segments. The complexes (there are different complexes for HPO 4 2− and for H 2PO 4 − [3]) form with concentrations of peptide in the range of hundreds of micromolar, making it significant in the biological context. NMR spectra provide changes in chemical shift as functions of both phosphate concentration and pH. The resulting curves show titration of the phosphate, with its standard pK. Possible implications for other anion–S4 interactions, including ion pairs rather than complexes, as with Cl −, are also discussed.