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PubMed1988

Phosphate inhibition of the human red cell sodium pump: simultaneous binding of adenosine triphosphate and phosphate.

1. The Na+-K+ exchange carried out by the Na+ pump of human red cell ghosts and the Na+ + K+-dependent adenosine triphosphatase (Na+,K+-ATPase) activity of human red cell membranes are inhibited by MgPO4 rather than by free phosphate; similarly, the substrate for the K+-K+ exchange carried out by the pump is MgPO4 rather than free phosphate. 2. Inhibition of the Na+, K+-ATPase activity by MgPO4 is only partially competitive (mixed type) with ATP, and MgPO4 inhibition of the Na+-K+ exchange measured in Na+-free solutions and in K+-free ghosts which contain ATP at relatively high concentration is partially uncompetitive (mixed type) with external K+. 3. When measurements were made in K+-free ghosts and Na+-free solutions, or when Na+,K+-ATPase activity was measured at high ATP concentrations, inhibition by MgPO4 was non-competitive with cell Na+. This observation is not consistent with the Albers-Post reaction mechanism of the Na+ pump, and suggests the presence of an alternative reaction pathway in which ATP combines with the enzyme before phosphate is released. 4. MgPO4 monotonically inhibited the uncoupled Na+ efflux which occurs in solutions free of both Na+ and K+. The uncoupled efflux seemed to be more sensitive to MgPO4 inhibition than the Na+-K+ exchange. 5. Trinitrophenyladenosine-5'-tetraphosphate stimulated the K+-K+ exchange in the presence of MgPO4, and the characteristics of stimulation by TNP adenosine tetraphosphate were little different from the characteristics of stimulation by trinitrophenyladenosine-5'-triphosphate or -5'-diphosphate. The nucleotide binding site at which K+-K+ exchange is stimulated must be able to accommodate a nucleotide with a linear array of four phosphate groups.

Adenosine Triphosphate↗

PubMed1987

Effect of bicarbonate and phosphate on renal phosphate leak in experimental Fanconi syndrome.

The role of acidosis in the renal phosphate leak in Fanconi syndrome (FS) was studied in maleate-induced FS in rats. Clearance studies were performed in the following groups: 1) intact rats served as control, 2) rats with maleate-induced FS, 3) rats with FS receiving intravenous bicarbonate (HCO3-), 4) intact rats receiving intravenous 0.03 N HCl (inducing acidosis similar to that of Group 2), 5) rats with FS receiving intravenous phosphate buffer and NaCl, and 6) rats with FS receiving intravenous phosphate buffer and bicarbonate similar to Group 3. In Group 2 serum pH and fractional excretion of phosphate (CP/GFR) averaged 7.31 +/- 0.08 (mean +/- SE) and 1.00 +/- 0.06, respectively, and differed significantly from Group 1, in which the corresponding values were 7.41 +/- 0.01 and 0.12 +/- 0.02, respectively. In Group 3, intravenous HCO3- corrected pH to 7.43 +/- 0.01 and reduced CP/GFR to 0.33 +/- 0.05, both results were different from the corresponding rates in Group 2 (P less than 0.0005). In Group 4, intravenous HCl reduced serum pH to 7.31 +/- 0.02 (P not significant as compared with Group 2) and increased CP/GFR to 0.186 +/- 0.030, the latter was higher than CP/GFR in control rats (P less than 0.01) but was lower than that in HCO3- -treated FS rats. In Group 5 serum pH was 7.31 +/- 0.021, similar to Group 2. CP/GFR was 0.84 +/- 0.031, significantly lower than in Group 2 (P less than 0.05). In Group 6 serum pH was 7.43 +/- 0.013 and CP/GFR was 0.86 +/- 0.044.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Nerve and muscle regeneration after axonal division in rats treated with isaxonine phosphate (isopropylamino-2-pyrimidine phosphate).

Isaxonine phosphate (isopropylamino-2-pyrimidine phosphate), a neurotrophic agent, was tested on Schwann cell and muscle metabolism as evidenced by radiophosphate uptake in the inorganic phosphate and organic-bound acid-soluble phosphate fractions. It had no demonstrable effect either on sciatic nerve Schwann cells above and below an experimental crush or on the corresponding gastrocnemius and soleus muscles in their denervated and reinnervated state (7th to 28th postoperative day). It also failed to influence the end results (150th postoperative day) at nerve and muscle level after surgical division of the nerve and repair by either microsuture or fibrinogen adhesive.

Animals↗

PubMedDate not supplied

Sodium d-fructose-1,6-diphosphate vs. sodium monohydrogen phosphate in total parenteral nutrition: a comparative in vitro assessment of calcium phosphate compatibility.

BACKGROUND: The supply of high amounts of calcium (Ca) and phosphorus (P) during total parenteral nutrition (TPN) is matter of concern because of the risk associated with calcium phosphate precipitation. The in vitro Ca-P compatibility in ready-for-use TPN solutions after the addition of different concentrations of inorganic phosphate or d-fructose-1,6-diphosphate (FDP) and calcium chloride was evaluated. METHODS: Four series of experiments for each Ca + P couple were carried out by varying amino acid concentrations (2% or 4%), temperature (25 degrees C or 37 degrees C), and pH. The extent of precipitation was estimated by visual inspection and particle count. The areas of maximal compatibility (ie, areas showing the complete absence of precipitates) were drawn from the precipitation curves. RESULTS: The precipitation extent was considerably higher in conditions mimicking body environment for both Ca + P couples. The compatibility area at 37 degrees C and 2% amino acid for CaCl2 + Na2HPO4 admixtures was included within 2.50 mmol/L CaCl2 and 2.22 mmol/L Na2HPO4, whereas that for CaCl2 + FDP was within 33.3 mmol/L CaCl2 and 10.0 mmol/L FDP (20 mEq/L of P). Unlike inorganic calcium phosphate, FDP dicalcium salt precipitation was kinetically delayed and was only minimally enhanced by decreasing amino acid concentration. CONCLUSIONS: Our data indicated that the use of FDP as the P source in parenteral nutrition solutions was effective in avoiding the life-threatening calcium phosphate precipitation. Thus, the addition of FDP to TPN admixtures represents a safe choice, allowing the simultaneous administration of high amounts of Ca and P in restricted fluid volumes, even at low amino acid concentrations.

Calcium↗

PubMed2005

Acute phosphate nephropathy following oral sodium phosphate bowel purgative: an underrecognized cause of chronic renal failure.

The findings of diffuse tubular injury with abundant tubular calcium phosphate deposits on renal biopsy are referred to as nephrocalcinosis, a condition typically associated with hypercalcemia. During the period from 2000 to 2004, 31 cases of nephrocalcinosis were identified among the 7349 native renal biopsies processed at Columbia University. Among the 31 patients, 21 presented with acute renal failure (ARF), were normocalcemic, and had a history of recent colonoscopy preceded by bowel cleansing with oral sodium phosphate solution (OSPS) or Visicol. Because the precipitant was OSPS rather than hypercalcemia, these cases are best termed acute phosphate nephropathy. The cohort of 21 patients with APhN was predominantly female (81.0%) and white (81.0%), with a mean age of 64.0 yr. Sixteen of the 21 patients had a history of hypertension, 14 (87.5%) of whom were receiving an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker. The mean baseline serum creatinine was 1.0 mg/dl, available within 4 mo of colonoscopy in 19 (90.5%) patients. Patients presented with ARF and a mean creatinine of 3.9 mg/dl at a median of 1 mo after colonoscopy. In a few patients, ARF was discovered within 3 d of colonoscopy, at which time hyperphosphatemia was documented. Patients had minimal proteinuria, normocalcemia, and bland urinary sediment. At follow-up (mean 16.7 mo), four patients had gone on to require permanent hemodialysis. The remaining 17 patients all have developed chronic renal insufficiency (mean serum creatinine, 2.4 mg/dl). Acute phosphate nephropathy is an underrecognized cause of acute and chronic renal failure. Potential etiologic factors include inadequate hydration (while receiving OSPS), increased patient age, a history of hypertension, and concurrent use of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker.

Acute Kidney Injury↗

PubMed1998

Dipyridamole decreases renal phosphate leak and augments serum phosphorus in patients with low renal phosphate threshold.

It has been shown that an acute infusion of dipyridamole increased renal phosphate reabsorption in rats and humans. A prospective study was performed to determine whether chronic treatment by dipyridamole given orally could decrease renal phosphate leak and increase serum phosphorus in patients with idiopathic low renal phosphate threshold (TmPO4/GFR < 0.77 mM). Sixty-four patients with low TmPO4/GFR were included and treated with dipyridamole (75 mg, 4 times daily) for more than 12 mo. Serum phosphorus, TmPO4/GFR, parathyroid hormone, serum calcium, and 1,25-dihydroxyvitamin D were measured sequentially before treatment, and after 3, 6 to 9, and 12 mo of treatment. Under chronic treatment with dipyridamole, TmPO4/GFR and serum phosphorus significantly increased in 80% of patients within 3 mo, with maximal values reached within 9 mo. This improvement persisted after 12 mo of treatment. In 28 patients, 1,25-dihydroxyvitamin D concentrations were above the normal range (> 42 pg/ml) and normalized in parallel with the increase of serum phosphorus. The 24-h calcium excretion (which was initially increased in patients with high vitamin D concentrations) and urolithiasis decreased under treatment. Ionized serum calcium and parathyroid hormone remained unchanged. After 2 yr, treatment was discontinued in three patients; serum phosphorus and TmPO4/GFR decreased within 1 mo after discontinuation. Dipyridamole at a dose of 75 mg 4 times daily increases low TmPO4/GFR and improves hypophosphatemia in patients with renal phosphate losses and can be used to treat these patients.

Administration, Oral↗

PubMed1978

Phosphate metabolism and glucose-initiated efflux of phosphate ions in islets of fetal pancreas.

Elsewhere we have proposed that the rapid transient efflux of 32P orthophosphate that occurs when prelabeled pancreatic islets are exposed to nutrient secretagogues (the "phosphate flush") reflects one of the earliest steps in islet stimulus-secretion coupling. We have now shown that the "phosphate flush" is much smaller with islets from fetal rats 21 1/2 days old. This could be attributed to decreased cellular stores of radioactivity, especially inorganic orthophosphate (32P), at the onset of stimulation, which may have been due, in part, to the diminished ability of fetal islets to retain the radiophosphorus accumulated during the labeling period. Certain other differences in phosphate metabolism were also observed. With prelabeled islets from adult rats, exposure to 3.0 mg. per milliliter glucose effected acute increases in the tissue content of AT32P and GT32P. Comparable stimulation of prelabeled fetal islets with 3.0 mg. per milliliter glucose did not elicit detectable changes in the labeling of ATP or GTP. The findings indicate that selected aspects of phosphate metabolism may be immature in fetal islets and, perhaps, implicated in their obtunded secretion of insulin in response to stimulation with glucose.

Adenosine Triphosphate↗

PubMed1993

Inositol glycan phosphate derived from human erythrocyte acetylcholinesterase glycolipid anchor and inositol cyclic 1,2-phosphate antagonize glucagon activation of glycogen phosphorylase.

In this study we examine the hypothesis that an inositol glycan phosphate can act similarly to insulin on intact cells. The inositol glycan phosphate used in this study (glycan alpha) was isolated previously from the glycoinositol phospholipid anchor of human erythrocyte acetylcholinesterase and was shown to have the structure glycine-ethanolamine-PO4-Man-Man-(N,N-dimethylethanolamine-PO4)Man- (N,N-dimethyl)GlcN-inositol-PO4. The cellular response investigated was the glucagon-stimulated activation of glycogen phosphorylase in rat hepatocytes. When hepatocytes were incubated with 20 nM glucagon for 4 min, the ratio of phosphorylase a activity to total phosphorylase increased from a basal value of 0.49 +/- 0.02 to 0.82 +/- 0.03 (mean +/- SE, n = 15). Inclusion of either 100 nM insulin or 3-10 microM glycan alpha during the glucagon incubation significantly decreased the glucagon-stimulated activity ratio to 0.74 +/- 0.03 for either agent. Furthermore, hepatocyte preparations differed in their response to insulin and were divided into insulin-responsive and -resistant groups. Glycan alpha had a significant effect only in the insulin-responsive group for which the observed activity ratio for 10 microM glycan alpha plus glucagon (0.68 +/- 0.05) compared closely with that for insulin plus glucagon (0.70 +/- 0.04). For the insulin-resistant group, the activity ratio in the presence of 10 microM glycan alpha was 0.81 +/- 0.03, unchanged from the control with glucagon alone. Because glycan alpha contains an inositol phosphate group, the effect of inositol cyclic 1,2-phosphate on the glucagon-stimulated activity ratio was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗

PubMed1992

The least number of phosphate groups for crosslinking of casein by colloidal calcium phosphate.

Artificial casein micelles were formed with whole human casein at 20 mM calcium, 17 mM phosphate, and 10 mM citrate. The casein micelles disaggregated by 6 M urea were separated by high performance gel chromatography on a TSK-GEL G4000SW column into crosslinked and monomeric fractions. When the crosslinked casein fraction was analyzed by high performance ionexchange chromatography on a TSK-GEL DEAE-5PW column, a small peak, representing the 3-P component of human beta-casein, and distinct peaks of the 4-P and 5-P components were found. Artificial casein micelles were formed from mixtures of each purified component of human beta-casein and bovine kappa-casein, disaggregated by urea, and separated on a TSK-GEL G4000SW column. The casein aggregates crosslinked by colloidal calcium phosphate were formed in artificial casein micelles of the 3-P and 4-P components. In contrast, no crosslinkage was formed in artificial micelles of the 1-P and 2-P components. The results indicate that at least three phosphate groups are needed for crosslinking of casein by colloidal calcium phosphate.

Animals↗

PubMed1985

[Uranium, thorium and potassium contents and radioactive equilibrium states of the uranium and thorium series nuclides in phosphate rocks and phosphate fertilizers].

Uranium, thorium and potassium contents and radioactive equilibrium states of the uranium and thorium series nuclides have been studied for 2 phosphate rocks and 7 phosphate fertilizers. Uranium contents were found to be rather high (39-117 ppm) except for phosphate rock from Kola. The uranium series nuclides were found to be in various equilibration states, which can be grouped into following three categories. Almost in the equilibrium state, 238U approximately 230Th greater than 210Pb greater than 226Ra and 238U greater than 230Th greater than 210Pb greater than 226Ra. Thorium contents were found to be, in general, low and appreciable disequilibrium of the thorium series nuclides was not observed except one sample. Potassium contents were also very low (less than 0.3% K2O) except for complex fertilizers. Based on the present data, discussions were made for the radiation exposure due to phosphate fertilizers.

Alpha Particles↗

PubMed2005

Recycling of used commercial phosphate-bonded investments with additional mono-ammonium phosphate.

Industrial waste is on the increase, resulting in severe environmental contamination. Against this background, this study sought to investigate the possibility of recycling used phosphate-bonded investments. Commercial phosphate-bonded investment was mixed and heated according to manufacturer's instructions, then powdered with a ball mill machine to be used as recycled investment (Code: R). Mono-ammonium phosphate (NH4H2PO4) of 2, 5, 8, 11, and 14 g were added to 100 g of R because of residual MgO, and coded as Ra, Rb, Rc, Rd, and Re respectively. Investment properties were then examined. Particle size of R was 50.66 microm and close to the original investment. It was found that more NH4H2PO4 led to larger setting expansion, smaller thermal expansion, and lower fired strength. The data of Re in these three aspects were 1.42 +/- 0.09%, 0.78 +/- 0.21%, and 8.85 +/- 0.88 MPa respectively, and differences against the original investment were significant. Ra showed significantly longer setting time than other investments. Based on the results of this study, we concluded that it was possible to set used phosphate-bonded investments by adding NH4H2PO4; in particular, Rd showed suitable expansion and acceptable mechanical properties.

Conservation of Natural Resources↗

PubMed1999

Lipid phosphate phosphohydrolase-1 degrades exogenous glycerolipid and sphingolipid phosphate esters.

Lipid phosphate phosphohydrolase (LPP)-1 cDNA was cloned from a rat liver cDNA library. It codes for a 32-kDa protein that shares 87 and 82% amino acid sequence identities with putative products of murine and human LPP-1 cDNAs, respectively. Membrane fractions of rat2 fibroblasts that stably expressed mouse or rat LPP-1 exhibited 3.1-3. 6-fold higher specific activities for phosphatidate dephosphorylation compared with vector controls. Increases in the dephosphorylation of lysophosphatidate, ceramide 1-phosphate, sphingosine 1-phosphate and diacylglycerol pyrophosphate were similar to those for phosphatidate. Rat2 fibroblasts expressing mouse LPP-1 cDNA showed 1.6-2.3-fold increases in the hydrolysis of exogenous lysophosphatidate, phosphatidate and ceramide 1-phosphate compared with vector control cells. Recombinant LPP-1 was located partially in plasma membranes with its C-terminus on the cytosolic surface. Lysophosphatidate dephosphorylation was inhibited by extracellular Ca2+ and this inhibition was diminished by extracellular Mg2+. Changing intracellular Ca2+ concentrations did not alter exogenous lysophosphatidate dephosphorylation significantly. Permeabilized fibroblasts showed relatively little latency for the dephosphorylation of exogenous lysophosphatidate. LPP-1 expression decreased the activation of mitogen-activated protein kinase and DNA synthesis by exogenous lysophosphatidate. The product of LPP-1 cDNA is concluded to act partly to degrade exogenous lysophosphatidate and thereby regulate its effects on cell signalling.

Animals↗

PubMed1975

Effects of pyridoxal phosphate N-oxide and 2'-hydroxy pyridoxal phosphate on L-aspartate beta-decarboxylase.

Pyridoxal phosphate N-oxide and 2'-hydroxypyridoxal phosphate served as the coenzyme for aspartate beta-decarboxylase (EC 4.1.1.12) from Pseudomonas dacunhae. Reconstituted enzymes with those pyridoxal phosphate analogues exhibited an absorption band near 370 nm. Close to 1 mole of vitamin B6 derivative is bound per minimal catalytic unit with high affinity. The decarboxylase, desulfinase, and transaminase activites of the both pyridoxal phosphate derivate-enzymes are relatively low. But the Km values for aspartate and cysteine sulfinate are not affected.

Aspartic Acid↗

PubMed1990

Inverse relation between plasma inorganic phosphate and phospholipids in mice: effect of dietary inorganic phosphate, fasting and glucagon.

We measured in mice under various conditions plasma phospholipids (PlipPl), total phosphate (PtotPl), inorganic phosphate (PiPl), and calculated other phosphate-containing material (PXPl) by subtracting (Plip + Pi)Pl from PtotPl. In mice fed low Pi diet (LPD) for 10 days, PlipPl was higher, PxPl did not change, whereas PiPl and PtotPl were lower than under high Pi diet (HPD). A highly significant inverse correlation was found between PlipPl and PiPl. The effect on PlipPl of maneuvers known to change PiPl acutely (within hours) was then investigated. In LPD mice, 6 h fasting, which increases PiPl, led to a decrease of PlipPl without significant changes of PtotPl and PxPl. The conspicuous rise in PiPl observed with glucagon treatment was associated with a decrement of PlipPl of the same magnitude as the increase in PiPl without a change of PtotPl or PxPl. Finally, injection of Pi lowered PlipPl in a dose-dependent manner within 2 h. In mice fed HPD, PlipPl decreased similarly during all acute maneuvers described under LPD, except Pi injection, where it did not decrease. In conclusion, the effects described above would suggest that the regulation of the two phosphate species may be linked and that PlipPl may possibly be involved in Pi homeostasis.

Animals↗

PubMed1987

Effect of phosphate on different blood parameters of labourers at Rusaifa Phosphate Mines, Jordan.

The effect of phosphate on PCV, Hb, platelet count, WBC count and differential leukocytic count were investigated in 36 phosphate mine labourers and 21 office employees (not exposed to phosphate dust) at Rusaifa Phosphate Mines, Jordan. Their age range was 30-40 years and they had worked in the mines for 5 to 10 years. Most parameters were significantly higher in the mine labourers as compared to those of office employees.

Adult↗

PubMed1981

Function of the phosphate group of pyridoxal 5'-phosphate in the glycogen phosphorylase reaction.

To understand the catalytic mechanism of glycogen phosphorylase (EC 2.4.1.1), pyridoxal(5')phospho(1)-beta-D-glucose was synthesized and examined as a hypothetical intermediate in the catalysis. Pyridoxal phosphoglucose bound stoichiometrically to the cofactor site of rabbit muscle phosphorylase b in a similar mode of binding to the natural cofactor, pyridoxal 5'-phosphate. The rate of binding of pyridoxal phosphoglucose was only 1/100 compared with that of pyridoxal phosphate. The enzyme reconstituted with pyridoxal phosphoglucose showed no enzymatic activity at all even after prolonged incubation of the enzyme with substrates and activator. The present data would contradict participation of the phosphate group of pyridoxal phosphate in a covalent glucosyl-enzyme intermediate even if the covalent intermediate was formed during the catalysis.

Animals↗

PubMed1982

Analysis of phosphate in serum with the phosphate redox electrode system.

A phosphate redox electrode system (PRES) was designed, constructed, and evaluated for analysis of inorganic phosphate in serum. This system is based on the observed phosphate ion potential of a chemically treated iron wire in a turbulent flow-through cell at constant oxygen tension. We analyzed 110 clinical samples by this technique and with the Technicon SMAC. Of the specimens analyzed, 32% contained abnormal phosphate concentrations. Each was assayed two to four times with the PRES and once with the SMAC. The PRES assay rate was 60 samples/h. Mean phosphorus concentrations (and SEM) were: PRES, range of values for replicate data sets, 30.5-31.0 (0.5-1.1) mg/L; SMAC, 30.8 (1.0) mg/L. Results for the PRES (y) correlated well with those by the SMAC: r = 0.968 to 0.980, estimated slope = 0.99 to 1.03, and estimated intercept = -1.1 to 0.1 mg/L. Differences in results by the two methods were not statistically significant.

Electrochemistry↗

PubMed1988

Properties of mannosyl- and N-acetylglucosamine-1-phosphate transferases towards dolichol phosphate in liver microsomes from pig embryos.

1. The activity of mannosyl- and N-acetylglucosamine-1-phosphate transferases in microsomes from pig embryonic liver was linear to 1 min of incubation at 37 degrees C. 2. The activity of both enzymes was higher in the presence of Mg2+ as compared to Mn2+. A maximal stimulatory effect of Mn2+ was obtained at 2 mM concentration and greater concentrations of it inhibited the activities of both enzymes. 3. The activity of mannosyl transferase was found to be highest after treatment of microsomes with Nonidet P-40 while the activity of N-acetylglucosamine-1-phosphate transferase was greatest in the presence of sodium deoxycholate. 4. The Km for acceptor substrate was 1.6 x 10(-5)M in the reaction for dolichol phosphate mannose synthesis and 2.2 x 10(-5)M in the reaction for dolichol pyrophosphate N-acetylglucosamine formation. 5. The Km for GDP-mannose was 1.4 x 10(-5)M and for UDP-N-acetylglucosamine-6.2 x 10(-5)M. At saturating concentrations of donor substrates V values (pmol/min/mg) were 1330 and 150, respectively.

Animals↗