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PubMed2005

High early strength calcium phosphate bone cement: effects of dicalcium phosphate dihydrate and absorbable fibers.

Calcium phosphate cement (CPC) sets in situ to form resorbable hydroxyapatite with chemical and crystallographic similarity to the apatite in human bones, hence it is highly promising for clinical applications. The objective of the present study was to develop a CPC that is fast setting and has high strength in the early stages of implantation. Two approaches were combined to impart high early strength to the cement: the use of dicalcium phosphate dihydrate with a high solubility (which formed the cement CPC(D)) instead of anhydrous dicalcium phosphate (which formed the conventional cement CPC(A)), and the incorporation of absorbable fibers. A 2 x 8 design was tested with two materials (CPC(A) and CPC(D)) and eight levels of cement reaction time: 15 min, 30 min, 1 h, 1.5 h, 2 h, 4 h, 8 h, and 24 h. An absorbable suture fiber was incorporated into cements at 25% volume fraction. The Gilmore needle method measured a hardening time of 15.8 min for CPC(D), five-fold faster than 81.5 min for CPC(A), at a powder:liquid ratio of 3:1. Scanning electron microscopy revealed the formation of nanosized rod-like hydroxyapatite crystals and platelet crystals in the cements. At 30 min, the flexural strength (mean +/- standard deviation; n = 5) was 0 MPa for CPC(A) (the paste did not set), (4.2 +/- 0.3) MPa for CPC(D), and (10.7 +/- 2.4) MPa for CPC(D)-fiber specimens, significantly different from each other (Tukey's at 0.95). The work of fracture (toughness) was increased by two orders of magnitude for the CPC(D)-fiber cement. The high early strength matched the reported strength for cancellous bone and sintered porous hydroxyapatite implants. The composite strength S(c) was correlated to the matrix strength S(m): S(c) = 2.16S(m). In summary, substantial early strength was imparted to a moldable, self-hardening and resorbable hydroxyapatite via two synergistic approaches: dicalcium phosphate dihydrate, and absorbable fibers. The new fast-setting and strong cement may help prevent catastrophic fracture or disintegration in moderate stress-bearing bone repairs.

Bone Substitutes↗
PubMed1983

Sequential processes of phosphate limitation and of phosphate release in streptomycin fermentations.

The significance of the sequential processes of phosphate limitation and of phosphate release from medium constituents is demonstrated in technical streptomycin fermentations. The phosphate limitation initiated the streptomycin synthesis as well as the formation of phosphatases and protease. In later periods of the process the phosphate release influences especially the enzyme formation.

Culture Media↗
PubMed1987

Ion-exchange resins as potential phosphate-binding agents for renal failure patients: effect of the physicochemical properties of resins on phosphate and bile salt binding.

The effect of resin type, degree of cross-linking, bead size, and surface area on the phosphate and bile salt binding characteristics of five strongly basic Dowex anion-exchange resins in the chloride form was studied. The maximum uptake of phosphate (expressed as uptake of phosphorus) from sodium phosphate solutions was 137, 82, 86, 138, and 76 mg of phosphorus per gram of dry Dowex resins XF 43311, XY 40013, XF 43254, XY 40011, and XY 40012, respectively. The presence of simulated gastric or intestinal fluids resulted in small but insignificant alterations in phosphorus uptake by the resins. The resins all bound similar amounts of phosphorus and taurocholate (80-100% of the total phosphorus and taurocholate in solution) at physiological concentrations of phosphate and bile salt. Dowex resins XY 40013 and XF 43254, with identical physicochemical properties, but different bead sizes and surface areas, bound similar amounts of the bile salt sodium taurocholate at all taurocholate concentrations, indicating that binding was not restricted to the surface sites on the resin bead. The 2% cross-linked resins bound 3-4 times more taurocholate than the 8% cross-linked resins (at high taurocholate concentrations); the smaller pore size of the latter resins probably presents a greater mechanical exclusion barrier than the larger pore size of the 2% cross-linked resins.

Anions↗
PubMed1996

Glucose 6-phosphate and mannose 6-phosphate are equally and more actively hydrolyzed by glucose 6-phosphatase during hysteretic transition within intact microsomal membrane than after detergent treatment.

We have studied the rapid kinetics of glucose-6-phosphatase (Glc6Pase) toward glucose 6-phosphate (Glc6P) and mannose 6-phosphate (Man6P) in intact and detergent-treated microsomes, using a radiometric assay based on the use of [U(-)14C]hexose 6-phosphates. We show that a hysteretic transition of Glc6Pase from a rapid hydrolytic form to slower kinetic form within the intact membrane occurs for both substrates with the same relaxation time. During the hysteretic transition, preceding the steady-state rate of hydrolysis, Glc6Pase is able to hydrolyze both Glc6P and Man6P at very similar rates. Only Glc6P is significantly hydrolyzed at steady state. Moreover, the initial rates of hydrolysis of both Glc6P and Man6P in intact microsomes are higher than the respective rates of hydrolysis after detergent treatment of the membrane at high substrate concentrations (10 and 20 microM), while these rates are not different at lower substrate concentrations. These data show that the marked specificity of Glc6Pase at steady state in the membrane is acquired owing to a hysteretic transition induced by the hydrolytic phenomenon, independently of the nature of the prior phosphate donor. The role of the membrane in this phenomenon is crucial, since the transition does not occur in its absence.

Animals↗
PubMed1995

Allosteric activation of rabbit reticulocyte guanine nucleotide exchange factor activity by sugar phosphates and inositol phosphates.

Sugar phosphates are required to maintain active rates of translation in gel-filtered rabbit reticulocyte lysates. They may stimulate polypeptide chain initiation by acting as NADPH generators or by a direct interaction with initiation factor(s). We now provide evidence for the allosteric activation of the purified guanine nucleotide exchange factor (eIF-2B) by sugar phosphates and inositol phosphates. In the presence of microM fructose 1,6-bisphosphate, the rate of eIF-2B-catalyzed GDP/GTP exchange is increased approximately 2-fold. The half-maximal concentration for stimulation of eIF-2B activity (SC50) is 57 microM. The binding of GTP to isolated eIF-2B is stimulated 1.5-fold, whereas GTP-binding to ALP-treated eIF-2B is not affected by sugar phosphates. Inositol 1,4-bisphosphate, like fructose 1,6-bisphosphate, stimulates 2-3-fold the activity of the isolated eIF-2B (SC50, 140 microM).

Allosteric Regulation↗
PubMed1989

Model of early self-replication based on covalent complementarity for a copolymer of glycerate-3-phosphate and glycerol-3-phosphate.

Glyceraldehyde-3-phosphate acts as the substrate in a model of early self-replication of a phosphodiester copolymer of glycerate-3-phosphate and glycerol-3-phosphate. This model of self-replication is based on covalent complementarity in which information transfer is mediated by a single covalent bond, in contrast to multiple weak interactions that establish complementarity in nucleic acid replication. This replication model is connected to contemporary biochemistry through its use of glyceraldehyde-3-phosphate, a central metabolite of glycolysis and photosynthesis.

Evolution, Molecular↗
PubMed2004

Trehalose biosynthesis in Thermus thermophilus RQ-1: biochemical properties of the trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase.

The genes for trehalose synthesis in Thermus thermophilus RQ-1, namely otsA [trehalose-phosphate synthase (TPS)], otsB [trehalose-phosphate phosphatase (TPP)], and treS [trehalose synthase (maltose converting) (TreS)] genes are structurally linked. The TPS/TPP pathway plays a role in osmoadaptation, since mutants unable to synthesize trehalose via this pathway were less osmotolerant, in trehalose-deprived medium, than the wild-type strain. The otsA and otsB genes have now been individually cloned and overexpressed in Escherichia coli and the corresponding recombinant enzymes purified. The apparent molecular masses of TPS and TPP were 52 and 26 kDa, respectively. The recombinant TPS utilized UDP-glucose, TDP-glucose, ADP-glucose, or GDP-glucose, in this order as glucosyl donors, and glucose-6-phosphate as the glucosyl acceptor to produce trehalose-6-phosphate (T6P). The recombinant TPP catalyzed the dephosphorylation of T6P to trehalose. This enzyme also dephosphorylated G6P, and this activity was enhanced by NDP-glucose. TPS had an optimal activity at about 98 degrees C and pH near 6.0; TPP had a maximal activity near 70 degrees C and at pH 7.0. The enzymes were extremely thermostable: at 100 degrees C, TPS had a half-life of 31 min, and TPP had a half-life of 40 min. The enzymes did not require the presence of divalent cations for activity; however, the presence of Co2+ and Mg2+ stimulates both TPS and TPP. This is the first report of the characterization of TPS and TPP from a thermophilic organism.

Adenosine Diphosphate↗
PubMed2005

Measurement of serum electrolytes and phosphate after sodium phosphate colonoscopy bowel preparation: an evaluation.

Our purpose was to observe the effects of sodium phosphate (NaP) colonoscopy preparation on serum electrolytes, phosphate, and calcium and to identify factors associated with any adverse effects. In an unselected group of 100 consecutive patients attending for out patient colonoscopy, 45% of patients had raised serum phosphate, which was positively correlated with creatinine and age. There was a negative association of phosphate with calcium; 16% of patients had hypocalcemia and 26% had hypokalemia. Patients taking ACE inhibitors, AT2 antagonists, or diuretics were associated with hyperphosphatemia. Significant electrolyte and metabolic disturbance from colonoscopy preparation has been shown with NaP preparation, without overt clinical effects. We recommend that elderly patients and those with significant comorbidity have their electrolytes and calcium measured, and diuretics and ACE inhibitors stopped, before NaP administration. Endoscopy units should be alert for patients who might be suffering from electrolyte disturbance postpreparation and be prepared to measure their electrolytes.

Adult↗
PubMed1984

Measurement of phosphate concentration in the presence of very labile phosphate esters.

There are a number of methods available for the measurement of phosphate ion concentration, which may be used when moderately labile phosphate esters such as ATP are present in low concentration. However, the highly acidic conditions usually employed make these unsuitable when very labile esters such as phosphocreatine are present. A method in which the phosphomolybdate complex is developed under mildly acidic conditions, using high molybdate concentrations to counteract the reduced assay sensitivity at high pH, is described. The assay is linear in the range 5-300 microM phosphate, and micromolar concentrations of phosphate can be reliably measured in the presence of millimolar phosphocreatine.

Adenosine Triphosphatases↗
PubMed1986

Modification of an essential amino group of phosphoenolpyruvate carboxylase from maize leaves by pyridoxal phosphate and by pyridoxal phosphate-sensitized photooxidation.

Phosphoenolpyruvate carboxylase from maize leaves was inactivated by pyridoxal 5'-phosphate in the dark and in the light. A two-step reversible mechanism is proposed for inactivation in the dark, which involves the formation of a noncovalent complex prior to a Schiff base with amino groups of the enzyme. Spectral analysis of pyridoxal 5'-phosphate-modified phosphoenolpyruvate carboxylase showed absorption maxima at 432 and 327 nm, before and after reduction with NaBH4, respectively, suggesting that epsilon-amino groups of lysine residues are the reactive groups in the enzyme. A correlation between spectral data and the maximal inactivation obtained with several concentrations of inhibitor allowed us to establish that the incorporation of 4 mol of pyridoxal 5'-phosphate per mole of holoenzyme accounts for total inactivation. The absence of modifier bound to phosphoenolpyruvate carboxylase when the modification was carried out in the presence of phosphoenolpyruvate and MgCl2 suggests the existence of an essential lysine residue at the catalytic site of the enzyme. Modification of phosphoenolpyruvate carboxylase in the light under an oxygen atmosphere resulted in an irreversible inactivation, which was completely protected by phosphoenolpyruvate and MgCl2. Spectral analysis of the photomodified enzyme showed an absorption peak of 320 nm, suggesting light-mediated addition of a nucleophilic residue (probably an imidazole group) to the pyridoxal 5'-phosphate-lysine azomethine bond.

Binding Sites↗
PubMed1991

Specific lipids enhance the activity of UDP-GlcNAc: dolichol phosphate GlcNAc-1-phosphate transferase in rat liver endoplasmic reticulum membrane vesicles.

The rate of the reaction catalyzed by UDP-N-acetylglucosamine (GlcNAc):dolichol phosphate GlcNAc-1-phosphate transferase in rat liver endoplasmic reticulum vesicles was shown to be influenced by particular lipids. Utilizing in vitro assay conditions where the membrane vesicles retained latency of glucose-6-phosphatase activity, the addition of phosphatidylethanolamine, cardiolipin, or monogalactosyldiglyceride resulted in severalfold increases in the rate of dolichol pyrophosphate N-acetylglucosamine synthesis. Other phospholipids were not stimulatory. These rates were dependent on the concentrations of the exogenous lipids and of the substrate dolichol phosphate. In the presence of cardiolipin, the membrane-bound enzyme became more susceptible to inactivation by protease K and to inhibition by tunicamycin. Titration of cardiolipin-containing endoplasmic reticulum vesicles with adriamycin indicated that the majority of the cardiolipin was exposed on the outer surface. These results suggest that the particular lipids altered membrane structure in a way that allowed further access of the enzyme to substrate, inhibitor, and other molecules. Lipids observed in these studies to be stimulatory are known to exist in the macromolecular hexagonal phase and may therefore be affecting the GlcNAc-1-phosphate transferase by locally disrupting the bilayer structure of the membrane. As other dolichol-utilizing enzymes have been previously observed by other investigators to be similarly influenced by such lipids, the effects may be common to enzymes of the dolichol cycle.

Animals↗
PubMed1978

The effect of sodium on inorganic phosphate- and p-nitrophenyl phosphate-facilitated ouabain binding to (Na+ + K+)-activated ATPase.

The effect of the hydrolysis product Pi and the artificial substrate p-nitrophenyl phosphate (p-nitrophenyl-P) on ouabain binding to (Na+ + K+)-activated ATPase was investigated. The hypothesis that (Mg2+ + p-nitrophenyl-P)-supported ouabain binding might be due to Pi release and thus (Mg2+ + Pi)-supported could not be confirmed. The enzyme . ouabain complexes obtained with different substrates were characterized according to their dissociation rates after removal of the ligands facilitating binding. The character of the enzyme . ouabain complex is determined primarily by the monovalent ion present during ouabain binding, but, qualitatively at least, it is immaterial whether binding was obtained with p-nitrophenyl phosphate or Pi. The presence or absence of Na+ during binding has a special influence upon the character of the enzyme . ouabian complex. Without Na+ and in the presence of Tris ions the complex obtained with (Mg2+ + Pi) and that obtained with (Mg2+ + p-nitrophenyl-P) behaved in a nearly identical manner, both exhibiting a slow decay. High Na+ concentration diminished the level of Pi-supported ouabain binding, having almost no effect on p-nitrophenyl phosphate-supported binding. Both enzyme . ouabain complexes, however, now resembled the form obtained with (Na+ + ATP), as judged from their dissociation rates and the K+ sensitivity of their decay. The complexes obtained at a high Na+ concentration underwent a very fast decay which could be slowed considerably after adding a low concentration of K+ to the resuspension medium. The most stable enzyme . ouabain complex was obtained in the presence of Tris ions only, irrespective of whether p-nitrophenyl phosphate of Pi facilitated complex formation. The presence of K+ gave rise to a complex whose dissociation rate was intermediate between those of the complexes obtained in the presence of Tris and a high Na+ concentration. It is proposed that the different ouabain dissociation rates reflect different reactive states of the enzyme. The resemblance between the observations obtained in phosphorylation and ouabain binding experiments is pointed out.

Adenosine Triphosphatases↗
PubMed1984

Enzymatic removal of alkaline phosphatase from renal brush-border membranes. Effect on phosphate transport and on phosphate binding.

Brush-border membrane vesicles prepared from rabbit kidney cortex were incubated at 37 degrees C for 30 min with phosphatidylinositol-specific phospholipase C. This maneuver resulted in a release of approx. 85% of the brush-border membrane-linked enzyme alkaline phosphatase as determined by its enzymatic activity. Transport of inorganic [32P]phosphate (100 microM) by the PI-specific phospholipase C-treated brush-border membrane vesicles was measured at 20-22 degrees C in the presence of an inwardly directed 100 mM Na+ gradient. Neither initial uptake rates, as estimated from 10-s uptake values (103.5 +/- 6.8%, n = 7 experiments), nor equilibrium uptake values, measured after 2 h (102 +/- 3.4%) were different from controls (100%). Control and PI-specific phospholipase C-treated brush-border membrane vesicles were extracted with chloroform/methanol to obtain a proteolipid fraction which has been shown to bind Pi with high affinity and specificity (Kessler, R.J., Vaughn, D.A. and Fanestil, D.D. (1982) J. Biol. Chem. 257, 14311-14317). Phosphate binding (at 10 microM Pi) by the extracted proteolipid was measured. No significant difference in binding was observed between the two types of preparations: 31.0 +/- 9.37 in controls and 29.8 +/- 8.3 nmol/mg protein in the proteolipid extracted from PI-specific phospholipase C-treated brush-border membrane vesicles. It appears therefore that alkaline phosphatase activity is essential neither for Pi transport by brush-border membrane vesicles nor for Pi binding by proteolipid extracted from brush-border membrane. These results dissociate alkaline phosphatase activity, but not brush-border membrane vesicle transport of phosphate, from phosphate binding by proteolipid.

Alkaline Phosphatase↗
PubMed1993

Anion transport through the phosphate-specific OprP-channel of the Pseudomonas aeruginosa outer membrane: effects of phosphate, di- and tribasic anions and of negatively-charged lipids.

The mechanism of anion transport through the phosphate-starvation inducible OprP-channel of Pseudomonas aeruginosa outer membrane was studied in planar lipid bilayer membranes. The single-channel conductance of OprP was 160 pS in 100 mM chloride solution. Addition of other anions, in particular of phosphate, di and tribasic anions lead to a strong decrease of the chloride conductance. The decrease was used to calculate the stability constants for the binding of these ions to the binding site of the channel on the basis of a one-site two-barrier model. The stability constant of the binding of phosphate to the site was 11,000 M-1 at neutral pH. Surprisingly, di- and tribasic anions, such as sulfate and citrate had a much lower affinity to the binding site inside the channel. Although the single-channel conductance was dependent on the external pH, the stability constants for phosphate binding decrease only slightly for increasing the pH. The use of negatively-charged lipids instead of neutral ones in the planar lipid bilayers had no influence on the single-channel conductance of the OprP-channel, suggesting that the channel is shielded from the influence of surrounding molecules. Its permeability properties are probably not influenced by negatively-charged lipopolysaccharide molecules.

Anions↗
PubMed1986

The interaction of phosphate with the purple acid phosphatase from beef spleen: evidence that phosphate binding is accompanied by oxidation of the iron chromophore.

Reaction of the reduced (pink) form of the purple acid phosphatase from beef spleen with excess phosphate at pH 5.0, monitored by optical and low temperature EPR spectroscopy and by measurement of enzymatic activity, results in parallel loss of activity and oxidation of the iron chromophore. Colorimetric and radiochemical (32P) experiments indicate the presence of one mole of tightly bound phosphate in the oxidized (purple) form of the enzyme; this phosphate is released upon reduction. Acid hydrolysis of 32P-phosphate-containing enzyme, followed by high voltage paper electrophoresis, gave no evidence for significant amounts of acid-stable phosphoamino acids.

Acid Phosphatase↗
PubMed1991

Effect of phosphate-regulating hormones on plasma composition, cardiovascular function, and parotid salivary phosphate secretion in red kangaroos (Macropus rufus).

The effects of administration of phosphate-regulating hormones on plasma composition, cardiovascular function, and secretion of phosphate and other electrolytes in parotid saliva were investigated in anesthetized red kangaroos. Plasma [PO4] was elevated by intravenous injections of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) at 5 or 12.5 nmol/12 hr for 72 hr but was unaltered by intravenous or intracarotid infusion of either salmon or porcine calcitonins at rates up to 3.2 IU min-1 for 60 min or by intracarotid infusions of the 1-34 amino acid fragments of rat, human, or bovine parathyroid hormones (PTH(1-34) at 350-460 pmol/min for 60 min. Plasma [Ca] fell during high-rate calcitonin infusion and rose during 1,25(OH)2D3 administration. PTH(1-34) infusion did not alter plasma [Ca] but did lower plasma [K] and arterial blood pressure and elevated heart rate and hematocrit. Salivary [PO4] and [Ca] and secretion rates were unaffected by the calcitonin infusions, by PTH(1-34) infusions, or by 1,25(OH)2D3 injection. Plasma and salivary concentrations of other ions were unaltered. These data provide evidence that kangaroo tissue can recognize and respond to all three types of phosphate-regulating hormones despite the peptides being foreign; however, the parotid gland of kangaroos, unlike the parotids of rats and sheep, did not respond and presumably lacks some component of the receptor-secretion couplings for these hormones. This independence of salivary PO4 secretion from hormonal regulation may be one of several adaptations which ensure relatively stable and adequate phosphate delivery to the foregut microorganisms despite an unreliable phosphorus intake in the natural diet.

Animals↗
PubMed1994

Long-term in vivo study of plasma-sprayed coatings on titanium alloys of tetracalcium phosphate, hydroxyapatite and alpha-tricalcium phosphate.

In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium plugs of standard size were implanted in dog femora. The bone bonding and bone formation of hydroxyapatite, alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate plasma-sprayed coatings were evaluated by mechanical push-out tests and histological observations after 3, 5, 15 and 28 months of implantation. During this time all coating types degraded. alpha-TCP showed the most significant degradation after 3 months of implantation. Hydroxyapatite and tetracalcium phosphate showed significant signs of degradation after about 5 months of implantation. All coatings showed a small increase in bone bonding after 5 months of implantation. In general, all types of implants showed similar bone response, some bone contact and several remodelling lacunae along the surfaces after long-term implantation.

Alloys↗
PubMed1995

Nuclear magnetic resonance investigation of the structures of phosphate and phosphate-containing glasses: a review.

This paper presents a review of the nuclear magnetic resonance (NMR) data for phosphate and phosphate-containing glasses obtained primarily within the past 10 years and of the structural interpretations based on those data. Compositions discussed include P2O5, alkali and alkaline earth phosphates, aluminophosphates, borophosphates, fluorophosphates, and phosphate-containing silicate and aluminosilicate glasses. 31P NMR data, in conjunction with 27Al, 29Si, 11B, 7Li, and 23Na data if appropriate, have proven very powerful in providing direct evidence about the local structural environments present in the these materials and in many cases have allowed interpretation of the physical and chemical behavior of these glasses in terms of polyhedral structures.

Alkalies↗