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PubMed1997

A phosphate-starvation-inducible outer-membrane protein of Pseudomonas fluorescens Ag1 as an immunological phosphate-starvation marker.

A phosphate-starvation-inducible outer-membrane protein of Pseudomonas fluorescens Ag1, expressed at phosphate concentrations below 0.08-0.13 mM, was purified and characterized. The purification method involved separation of outer-membrane proteins by SDS-PAGE and extraction of the protein from nitrocellulose or PVDF membranes after electrotransfer of proteins to the membranes. The N-terminal amino acid sequence of the purified protein, called Psi1, did not show homology to any known proteins, and in contrast to the phosphate-specific porin OprP of P. aeruginosa its mobility in SDS-PAGE was not affected by solubilization temperature. An antiserum against Psi1 recognized a protein of M, 55,000 in four other P. fluorescens strains among 24 tested strains representing Pseudomonas rRNA homology group I, showing antigenic heterogeneity within this group. A method for immunofluorescence microscopy involving cell permeabilization was adapted to visualize cell-specific expression of Psi1 in P. fluorescens exposed to limiting amounts of phosphate. This approach should be useful for further exploration of Psi1 as a marker to study the availability of phosphate to P. fluorescens in natural environments.

Amino Acid Sequence↗

PubMed2005

Structures of Mycobacterium tuberculosispyridoxine 5'-phosphate oxidase and its complexes with flavin mononucleotide and pyridoxal 5'-phosphate.

The X-ray crystal structure of a conserved hypothetical protein of molecular weight 16.3 kDa from Mycobacterium tuberculosis corresponding to open reading frame (ORF) Rv1155 has been solved by the multiwavelength anomalous dispersion method and refined at 1.8 A resolution. The crystal structure revealed that Rv1155 is a dimer in the crystal and that each monomer folds into a large and a small domain; the large domain is a six-stranded antiparallel beta-barrel flanked by two small alpha-helices and the small domain is a helix-loop-helix motif. The dimer interface is formed by residues protruding primarily from five of the six beta-strands in each subunit. Based on structural similarity and on ligand binding, it has been established that Rv1155 is a pyridoxine 5'-phosphate oxidase, the Escherichia coli and human counterparts of which catalyse the terminal step in the biosynthesis of pyridoxal 5'-phosphate (PLP), a cofactor used by many enzymes involved in amino-acid metabolism. The structures of flavin mononucleotide (FMN) and pyridoxal 5'-phosphate (PLP) bound separately to Rv1155 have been determined at 2.2 and 1.7 A resolution, respectively. Only one monomer binds non-covalently to one FMN molecule or to one PLP molecule. Arg55 and Lys57 are the key residues making hydrogen bonds and ionic interactions with the phosphate and ribose groups of the FMN molecule, whereas Arg55 and Arg129 provide hydrogen bonds and ionic interactions with the phosphate group of the PLP. Structural comparisons of Rv1155 from M. tuberculosis with its E. coli and human counterparts demonstrate that the core structure is highly conserved and the FMN-binding site is similarly disposed in each of the structures.

Amino Acid Sequence↗

PubMed2005

Efficacy and tolerability of a new formulation of sodium phosphate tablets (INKP-101), and a reduced sodium phosphate dose, in colon cleansing: a single-center open-label pilot trial.

BACKGROUND: The tablet form of sodium phosphate for bowel preparation for colonoscopy contains microcrystalline cellulose. This inactive ingredient produces a residue that obscures mucosal visualization and is time-consuming to remove during colonoscopy. AIM: To perform an open-label study of efficacy and tolerability of a modified formulation with microcrystalline cellulose reduced by 50% (code named INKP-101) and a lower total dose of sodium phosphate. METHODS: Patients scheduled for colonoscopy self-administered 28 INKP-101 tablets (42 g sodium phosphate). Colon cleansing efficacy was evaluated using a standard 4-point scoring system and the amount of microcrystalline cellulose present and time spent removing it using an 8-point scale. RESULTS: A total of 31 patients were screened and enrolled. Thirty patients had a colonoscopy and were evaluated for colon cleansing efficacy. Overall colon cleansing was rated as excellent and good in 90% and 10% of patients respectively. About 77% of patients had microcrystalline cellulose scores of 2 or 3 (corresponding to <1 or 1-2 min spent removing microcrystalline cellulose, respectively). The drug was well-tolerated and adverse events were generally benign. CONCLUSION: A new formulation of sodium phosphate with reduced microcrystalline cellulose and a lower total dose of sodium phosphate was effective for colonoscopy and well-tolerated.

Adult↗

PubMed1989

Changes in serum phosphate during beta-blockade in healthy men are not due to changes in the renal handling of phosphate.

Serum parathyroid hormone (PTH), phosphate, ionized calcium, magnesium, alkaline phosphatase and creatinine and the urinary excretion of phosphate and creatinine were studied after 1 and 3 weeks beta-blockade in 32 young healthy men given either atenolol at 50 mg, metoprolol at 100 mg, propranolol at 80 mg or placebo twice a day. After 1 week treatment serum phosphate (mean (range] increased in the propranolol-treated subjects (1.17 (0.99-1.30) to 1.32 (1.08-1.71) mmol l-1 (P = 0.03), minor changes were found in the atenolol and the metoprolol-treated subjects but not in the placebo group. Serum phosphate was unchanged compared to pretreatment values after 3 weeks. Renal clearance and urinary excretion of phosphate and creatinine was unchanged after both 1 and 3-weeks treatment. Serum PTH, ionized calcium, magnesium and alkaline phosphatase were unchanged in all groups, whereas serum urate and creatinine increased in the metoprolol-treated subjects after both 1 and 3 weeks.

Adult↗

PubMed1971

Experiments on the liberation of phosphate from the muscles of the human forearm during vigorous exercise and on the action of sodium phosphate on forearm muscle blood vessels.

1. During vigorous sustained or rhythmic exercise of the forearm muscles, plasma phosphate in the venous effluent from the active muscles increased by about 20%.2. The forearm muscles liberate phosphate during vigorous activity. This confirms observations made by Hilton & Vrbová (1970) on fast muscles in the cat.3. Infusions of sodium phosphate into the brachial artery which raised plasma phosphate in the venous effluent from the resting muscles by 400% had no effect upon the rate of the forearm blood flow.4. These results do not suggest that the liberation of phosphate plays any significant part in mediating the vasodilatation accompanying vigorous exercise of the muscles in the forearm.

Brachial Artery↗

PubMed1968

Trehalose phosphate synthesis in Streptomyces hygroscopicus: purification of guanosine diphosphate D-glucose: D-glucose-6-phosphate 1-glucosyl-transferase.

Guanosine diphosphate d-glucose:d-glucose-6-phosphate 1-glucosyl-transferase was purified approximately 100-fold from extracts of Streptomyces hygroscopicus. The purified enzyme catalyzed the transfer of glucose from guanosine diphosphate-d-glucose to glucose-6-phosphate to form trehalose phosphate and guanosine diphosphate. The enzyme was specific for these two substrates and was stimulated by the addition of magnesium ions. The product was characterized as alpha-alpha-trehalose-6-phosphate by its physical and chemical properties. The enzyme was present in a large number of Streptomyces species, suggesting that this group of organisms synthesized trehalose phosphate in a unique manner. This enzyme was not detected in fungi, since these organisms utilized uridine diphosphate-d-glucose as the glucosyl donor.

Carbon Isotopes↗

PubMed1985

Adaptation of phosphate transport in phosphate-deprived LLC-PK1 cells.

Sodium-dependent transport of phosphate was studied in LLC-PK1 cells that had been deprived of phosphate (Pi). Compared with control cells (fed with 2 mM Pi) a twofold increase in the rate of Na-Pi cotransport was observed in cells incubated for 15 h in a phosphate-free medium, whereas transport of L-alanine and the specific activity of alkaline phosphatase were not changed. The same adaptive response was observed with apical membrane vesicles isolated from Pi-deprived cells. In both experimental systems Pi deprivation caused a change in the Vmax but not in the apparent Km (for Pi) of the cotransport system. Adaptation of the Na-Pi cotransport was triggered by free phosphate concentrations between 0 and 100 microM. Over the first 20 h the adaptive response was found to be a linear process that could be prevented by 70 microM cycloheximide. Adapted cells that were re-treated with phosphate showed a rapid (less than 3 h) decrease in the Na-Pi transport. The data suggest that LLC-PK1 cells adapt to low Pi conditions by increasing the rate of the Na-Pi cotransport, which is located in the apical membrane. Two mechanisms may be involved in the adaptive response: a long-term process involving new protein synthesis, and a short-term response involving activation-inactivation of transport systems already existing.

Adaptation, Physiological↗

PubMed1986

Inactivation and degradation of yeast glucose-6-phosphate dehydrogenase selectively modified by pyridoxal-5-phosphate.

Modification by pyridoxal-5-phosphate of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) purified from Saccharomyces cerevisiae produces an inactivation effect, partially reversible by dilution in the presence of substrates. Spectroscopic analysis of the enzyme pyridoxal-5-phosphate complex reduced with NaBH4 provides the values expected for the binding of the aldehydic group to Lys residue. One Lys residue appears to be responsible for the observed enzyme inactivation, and the presence of the phosphate group is required for the effect. Besides the change of activity, the binding of pyridoxal-5-phosphate to the enzyme causes an increase in susceptibility to degradation by the intracellular yeast proteinase A at pH 7.6.

Aspartic Acid Endopeptidases↗

PubMed1994

Occlusion of dentinal tubules with calcium phosphate using acidic calcium phosphate solution followed by neutralization.

The occlusion of dentinal tubules with calcium phosphate, by a calcium phosphate precipitation method (CPP method), was investigated in vitro for evaluation of the potential value of this method for the treatment of dentin hypersensitivity. The method consists of treating the dentinal surface with a CPP solution, i.e., an acidic solution that contains both calcium and phosphate, followed by neutralization with basic post-treatment solution. The CPP solutions used in this study ([Ca] = 0.2 - 1.0 mol/L, [PO4] = 0.2 - 4.0 mol/L) were prepared by dissolving Ca(OH)2 or CaHPO4 x 2H2O in H3PO4 or HCl, and 1 mol/L NaOH solution was used for the post-treatment solution. Sections of human dentin disks treated by the CPP method were observed by scanning electron microscopy, and the precipitate in the dentinal tubules was subjected to x-ray micro-analysis. After treatment by the CPP method, dentinal tubules were occluded to a distance of approximately 15 microns from the surface, and the precipitate showed a Ca/P molar ratio of 1.03 +/- 0.01 To obtain a larger amount of precipitated mineral for further analysis, we used the same procedure with glass tubes (inside diameter, 1 mm). Powder x-ray diffraction analysis and FT-IR measurement revealed that the precipitate was dicalcium phosphate dihydrate (CaHPO4 x 2H2O). The instant precipitation of calcium phosphate mineral in the dentinal tubules demonstrated the potential value of the CPP method for the occlusion of dentinal tubules, this occlusion may be useful for the treatment of dentin hypersensitivity.

Calcium Phosphates↗

PubMedDate not supplied

Pathologic effects of butylated triphenyl phosphate-based hydraulic fluid and tricresyl phosphate on the adrenal gland, ovary, and testis in the Fischer-344 rat.

Triaryl phosphates including tricresyl phosphate (TCP) and butylated triphenyl phosphates (BTPs) are used in the commercial manufacture of plastics, lubricants, and hydraulic fluids. Recent reports implicate these compounds as endocrine and reproductive toxicants in rodents. The objectives of this study were to develop and characterize a rat model to investigate the mechanism(s) of toxicity of triaryl phosphate-based hydraulic fluids and to elucidate potential mechanistic pathways of toxicity through studies of structural/functional relationships. Groups of male and female rats received daily oral doses of either sesame oil alone or 1.7 g/kg of BTP or 0.4 g/kg TCP in sesame oil vehicle or 2.8 g/kg neat BTP for 20, 40, and 60 days. Light microscopic, morphometric, ultrastructural, and histochemical studies revealed hypertrophy and cholesteryl lipidosis of adrenocortical (both sexes) and ovarian interstitial cells that were progressive with duration of exposure. Minimal degeneration was observed in the adrenal cortex and ovary. TCP caused the most severe lesions in both the adrenal gland and ovary, but the morphologic and histochemical changes produced were similar for both compounds, suggesting a common mechanism of toxicity. Decreased testicular weight and degeneration of seminiferous tubules were detected only in TCP-treated rats. The Fischer-344 rat model using TCP and BTP administered by gavage is a valuable system to study mechanisms of endocrine and reproductive toxicity induced by triaryl phosphate-based hydraulic fluids.

Adrenal Cortex↗

PubMedDate not supplied

6-phosphogluconate dehydrogenase, glucose-6-phosphate dehydrogenase, glucose-6-phosphate isomerase, and hexokinase activity ratios in some human tumor cytosols.

The ratios of some key enzymatic activities of carbohydrate metabolism have been measured in human tumor cytosols. The activities of whole hexokinase (low Km, EC 2.7.1.1 and high Km, EC 2.7.1.2), 6-phosphogluconate dehydrogenase (EC 1.1.1.43), glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and glucose-6-phosphate isomerase (EC 5.3.1.9) change according to a biochemical pattern coherent with cell growth requirements. 6-phosphogluconate dehydrogenase activity was in each sample tested higher than glucose-6-phosphate dehydrogenase activity; this indicates that 6-phosphogluconate, a powerful inhibitor of glucose-6-phosphate isomerase, is unlikely to accumulate and inhibit this enzyme and glucose-6-phosphate channelling into glycolysis.

Cytosol↗

PubMed2000

Glucose-6-phosphate dehydrogenase and the oxidative pentose phosphate cycle protect cells against apoptosis induced by low doses of ionizing radiation.

The initial and rate-limiting enzyme of the oxidative pentose phosphate shunt, glucose-6-phosphate dehydrogenase (G6PD), is inhibited by NADPH and stimulated by NADP(+). Hence, under normal growth conditions, where NADPH levels exceed NADP(+) levels by as much as 100-fold, the activity of the pentose phosphate cycle is extremely low. However, during oxidant stress, pentose phosphate cycle activity can increase by as much as 200-fold over basal levels, to maintain the cytosolic reducing environment. G6PD-deficient (G6PD(-)) cell lines are sensitive to toxicity induced by chemical oxidants and ionizing radiation. Compared to wild-type CHO cells, enhanced sensitivity to ionizing radiation was observed for G6PD(-) cells exposed to single-dose or fractionated radiation. Fitting the single-dose radiation response data to the linear-quadratic model of radiation-induced cytotoxicity, we found that the G6PD(-) cells exhibited a significant enhancement in the alpha component of radiation-induced cell killing, while the values obtained for the beta component were similar in both the G6PD(-) and wild-type CHO cell lines. Here we report that the enhanced alpha component of radiation-induced cell killing is associated with a significant increase in the incidence of ionizing radiation-induced apoptosis in the G6PD(-) cells. These data suggest that G6PD and the oxidative pentose phosphate shunt protect cells from ionizing radiation-induced cell killing by limiting the incidence of radiation-induced apoptosis. The sensitivity to radiation-induced apoptosis was lost when the cDNA for wild-type G6PD was transfected into the G6PD(-) cell lines. Depleting GSH with l-BSO enhanced apoptosis of K1 cells while having no effect in the G6PD(-) cell line

Animals↗

PubMed1986

Phosphate metabolism and foetal growth in the rat. III. Net transfer of 31P and 32P inorganic phosphate from the maternal plasma to the placenta after foetectomy.

In primigravid rat females at the 12th day or later stages of gestation one foetus is surgically removed and the amniotic sac allowed to retract freely around the remaining placenta in situ. One hour to 10 days after foetectomy [32P]ortho-phosphate is injected intraperitoneally. The post-foetectomy placenta and matched normal placenta and foetus in the contralateral horn are taken after labelling periods of one or three hours and analysed for calcium, inorganic phosphate, organic-bound acid-soluble and organic-bound acid-insoluble phosphates in their [31P] and [32P] forms. The acutely foetectomized placenta--up to 24 hours after surgery--may serve as an appropriate model of the physiologically functioning syncytiotrophoblast: it is indeed noteworthy that organic-bound phosphate placental concentrations and labelling are little affected in the early post-foetectomy stages. On the other hand the placental inorganic phosphate concentration and labelling are profoundly affected by foetectomy. A surplus radioactive incorporation in the Pi fraction is observed which is strongly related to the weight of the control foetus and may represent up to twelve times the label incorporation in the control placenta; it decreases as the time interval since foetectomy lengthens. A cumulative increase in Pi concentration is observed which is strongly related to calcium concentration and may reach twenty-five times the maternal plasma Pi concentration. The presence of two independent pools of Pi is suggested: one geared to the metabolic needs of the placenta itself, the other representing the Pi normally transported to the foetus under metabolic control by the latter. The possibility of an electroneutral PO4(2-)/Ca2+ co-transport is evoked.

Animals↗

PubMed1984

Effect of parathyroid hormone on total phosphate and inorganic phosphate in blood, plasma, and urine of domestic fowl.

Previous work has shown that parathyroid hormone causes the kidneys of domestic fowl to secrete inorganic phosphate (Pi) into the urine. Secreted Pi is not derived directly from plasma Pi. The objective of the present study was to determine if direct or indirect correlations exist between the urinary Pi excretion rate and the concentration of phosphate in plasma or whole blood. Parathyroid hormone dissolved in gelatin carrier vehicle was injected into immature domestic fowl to cause net renal Pi secretion. Control birds were injected with carrier vehicle alone, resulting in net Pi reabsorption. Urine, plasma, and whole blood samples obtained during net Pi secretion were compared with samples obtained during net Pi reabsorption. Each sample was assayed for total and inorganic phosphate. Neither time course nor point by point comparisons of individual samples provided any evidence that secreted Pi is derived from organic phosphate in plasma or whole blood. These experiments suggest that phosphate pools within the kidneys may serve as a source for the Pi that is secreted in response to parathyroid hormone.

Animals↗

PubMed1991

Inositol-1,2-cyclic-phosphate 2-inositolphosphohydrolase. Substrate specificity and regulation of activity by phospholipids, metal ion chelators, and inositol 2-phosphate.

Glycerophosphoinositol (GroPIns) is a major inositol phosphate in many cell types. In this study we have determined the optimal conditions (pH 8.0 and 0.5 mM MnCl2) for the metabolism of this molecule in an extract from human placenta, and we show that the major product is inositol (1)-phosphate (Ins(1)P). The enzyme activity that catalyzes this reaction is contained in the same protein designated previously as inositol-(1,2)-cyclic-phosphate 2-inositolphosphohydrolase (cyclic hydrolase), a phosphodiesterase that catalyzes the conversion of inositol-(1,2)-cyclic phosphate (cIns(1,2)P) to Ins(1)P. In addition, the enzyme also catalyzes the production of Ins(1)P from inositol (1)-methylphosphate. All of these substrates, (cIns(1,2)P, GroPIns, and inositol (1)-methylphosphate), contain a phosphodiester bond at the 1-position of the inositol ring. Additional phosphate groups on the 4- or 5-positions of the inositol ring prevent hydrolysis by cyclic hydrolase. The Km of the enzyme for GroPIns is 0.67 mM, and the Vm is 5 mumol/min/mg of protein. GroPIns competitively inhibits cIns(1,2)P hydrolysis with a Ki equal to its Km as a substrate. Hydrolysis of GroPIns and cIns(1,2)P is stimulated by MnCl2, phosphatidylserine, and [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA). However, whereas cIns(1,2)P hydrolysis is increased 5-8-fold by phosphatidylserine and EGTA only a 2-fold increase of GroPIns hydrolysis occurs under the same conditions. Hydrolysis of both GroPIns and cIns(1,2)P is inhibited by Ins(2)P; the ID50 values are 12 and 1 microM, respectively. There are significant quantities of GroPIns and Ins(2)P in 3T3 cells, indicating that these compounds that alter cIns(1,2)P hydrolase activity may modulate intracellular levels of cIns(1,2)P. Finally, we present evidence suggesting that the substrate specificity of this enzyme is altered during cell transformation.

Animals↗

PubMed1989

Activation of glutamate by gamma-glutamate kinase: formation of gamma-cis-cycloglutamyl phosphate, an analog of gamma-glutamyl phosphate.

gamma-Glutamate kinase, the enzyme that catalyzes the first step in the pathway from glutamate to proline, has been postulated to convert glutamate to a gamma-activated form (possibly gamma-glutamyl phosphate), which is reduced by a NADPH-linked reductase to yield glutamate gamma-semialdehyde (in equilibrium with delta 1-pyrroline-5-carboxylate). In the present work we found that the kinase, in the absence or presence of the reductase (and in the absence of NADPH), catalyzes stoichiometric formation of 5-oxo-L-proline and Pi from L-glutamate and ATP, but catalyzes hydroxamate formation at only about 10% of the rate of ATP-cleavage. A new substrate of the kinase was found; thus, cis-cycloglutamate (cis-1-amino-1,3-dicarboxycyclohexane), a glutamate analog which cannot cyclize to form an analog of 5-oxoproline, interacts effectively with the kinase. The trans form of cycloglutamate does not interact with the kinase; only the cis form can assume a diequatorial conformation equivalent to the extended conformation of glutamate. cis-Cycloglutamyl phosphate formation was shown and evidence was obtained for formation of an enzyme-ADP-cycloglutamyl phosphate complex. Although cis-cycloglutamyl phosphate is not a reducible substrate of the NADPH-dependent reductase, the findings indicate that it interacts with the reductase. These studies, which elucidate several aspects of the mechanism of the utilization of glutamate for formation of delta 1-pyrroline-5-carboxylate, support the hypothesis that the kinase and reductase function as an enzyme complex. A model is suggested in which gamma-glutamyl phosphate formed on the kinase interacts with the reductase to form a gamma-glutamyl-reductase complex, which is reduced by NADPH to yield glutamate gamma-semialdehyde.

Adenosine Diphosphate↗

PubMedDate not supplied

[Phosphate inhibition of the conversion of ribose-1-phosphate--a product of purine nucleoside phosphorylase splitting in the phosphoribomutase reaction].

Different phosphate concentrations were studied for their effect on the degradation of adenosine by rat liver homogenates. It is shown that phosphate considerably inhibits the phosphoribomutase reaction without a significant effect on adenosine deaminase and purine nucleoside phosphorylase activities, that leads to the ribose-1-phosphate accumulation and to the disturbance of nucleoside utilization in reactions of the pentose phosphate pathway. It is supposed that the inhibition of the phosphoribomutase reaction by phosphate is important for regulation of nucleoside and nucleotide formation in a cell.

Adenosine↗

PubMed1983

Yeast carbamyl phosphate synthetase. Structure of the yeast gene and homology to Escherichia coli carbamyl phosphate synthetase.

A cloned fragment of yeast chromosomal DNA carrying the gene CPA2 coding for the large subunit of arginine-specific carbamyl phosphate synthetase has been sequenced. The cloned DNA has a 3,354-nucleotide long continuous reading frame coding for a polypeptide of 1,117 amino acids. The calculated molecular weight of the encoded polypeptide is 123,787, in good agreement with the reported molecular weight of the yeast carbamyl phosphate synthetase large subunit. The amino acid sequence of yeast carbamyl phosphate synthetase is homologous to the recently determined sequence of Escherichia coli carbamyl phosphate synthetase (Nyunoya, H., and Lusty, C. J. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 4629-4633) over almost the entire length of the protein. Like the E. coli large subunit, the yeast enzyme exhibits an extensive internal homology between its NH2- and carboxyl-terminal halves. The internal homology in both the yeast and E. coli proteins indicates that the gene coding for the large subunit of carbamyl phosphate synthetase was derived from a tandem duplication which occurred prior to the divergence of eukaryotes and prokaryotes.

Amino Acid Sequence↗