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PubMed2002

Implanted octacalcium phosphate is more resorbable than beta-tricalcium phosphate and hydroxyapatite.

Our previous studies have suggested that synthetic octacalcium phosphate (OCP) could be resorbed and replaced by newly formed bone if implanted in rat skull defects. We hypothesized that the implanted OCP is more resorbable than other commonly used bone graft substitutes of calcium phosphate compounds, such as hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP). To test the hypothesis, the present study was designed to compare histomorphometrically resorption of the implanted OCP, HA, and beta-TCP, which were kept in the experimental cranial defect of rats for a long term. A full thickness of standardized trephine defect was made in the rat parietal bone, and the same volume of granules of OCP, HA, and beta-TCP were implanted into the defect. Five specimens of each group were fixed 6 months after implantation. The percentage of remaining implants (r-Imp%) and newly formed bone (n-Bone%) in the defect was analyzed histomorphometrically. The statistical analysis showed that the r-Imp% of OCP was significantly lower than that of HA and beta-TCP. In contrast, the n-Bone% of OCP was significantly higher than that of HA and beta-TCP. The present study has shown that the implanted OCP in the rat cranial defect is more resorbable than the implanted beta-TCP and HA, whereas the implanted OCP enhances bone formation more than the implanted beta-TCP and HA.

Animals↗
PubMed2003

Long-term craniofacial osteoblast culture on a sodium phosphate and a calcium/sodium phosphate glass.

The aim of this study was to determine the characteristics of human craniofacial osteoblasts cultured on sodium phosphate glass and calcium-sodium phosphate glass in a long-term culture of up to 28 days. The characteristics studied were attachment, proliferation, alkaline phosphatase activity, collagen-1 production, and mineralization. A comparison of the degradation rate, measured by mass loss of the glasses, which are intended for use as a component of a novel degradable composite for craniofacial bone repair, was also performed. It was our hypothesis that the glass would be degradable with a change in degradation rate observed by calcium addition and support osteoblast proliferation and expression of the above characteristics. The inclusion of calcium into the reaction mixture significantly decreased the degradation rate, and it is suggested that the slower degradation is the result of pseudo crosslinking (ionic crosslinks rather than covalent bonding) of the polyphosphate chains by the calcium ions. Therefore, twice as many P-O bonds will need to be hydrolyzed for dissolution of the metal phosphate to occur, therefore greatly reducing the rate of hydrolysis. Osteoblasts were able to attach, spread, and proliferate in a manner comparable with the positive control, as shown by analysis of variance. Formation of a collagen-rich mineralized matrix was also observed. The results presented here suggest that a biocompatible soluble glass has been produced, which has potential to be included in a novel biodegradable craniofacial implant.

Calcium↗
PubMed2007

Phosphatidic acid regulates the affinity of the murine phosphatidylinositol 4-phosphate 5-kinase-Ibeta for phosphatidylinositol-4-phosphate.

Type I phosphatidylinositol 4-phosphate 5-kinase (PI4P5K) catalyzes the phosphorylation of phosphatidylinositol 4 phosphate [PI(4)P] at carbon 5, producing phosphatidylinositol 4,5 bisphosphate [PI(4,5)P2]. Phosphatidic acid (PA) activates PI4P5K in vitro and plays a central role in the activation of PIP5K pathways in vivo. This report demonstrates that actin fiber formation in murine fibroblasts involves PA activation of PIP5Ks and defines biochemical interactions between PA and the PIP5Ks. Inhibition of phospholipase D production of PA results in the loss of actin fibers. Overexpression of the beta isoform of the type I murine phosphatidylinositol 4-phosphate 5-kinase (mPIP5K-Ibeta) maintains actin fiber structure in the face of phospholipase D inhibition. PA activates mPIP5K-Ibeta by direct binding to mPIP5K-Ibeta through both electrostatic and hydrophobic interactions, with the fatty acid acyl chain length and degree of saturation acting as critical determinants of binding and activation. Furthermore, kinetic analysis suggests that phosphorylation of the PI(4)P substrate does not follow classical Michaelis-Menten kinetics. Instead, the kinetic data are consistent with a model in which mPIP5K-Ibeta initially binds to the lipid micelle and subsequently binds the PI(4)P substrate. In addition, the kinetics indicate substrate inhibition, suggesting that mPIP5K-Ibeta contains an inhibitory PI(4)P-binding site. These results suggest a model in which mPIP5K-Ibeta is surrounded by PI(4)P, but is unable to catalyze its conversion to PI(4,5)P2 unless PA is bound.

Actin Cytoskeleton↗
PubMed1981

[Cell wall polysaccharide structure in the food protein yeast, Candida spec. H. II. Characterization of phosphate binding to the mannan-protein-phosphate complex and identification of phosphodiester-bound mono- oligosaccharides].

The proteophosphomannan (PPM) obtained by extraction with citrate buffer, purification by the cetavlon method and gel filtration contains a high proportion of diesterified phosphate groups between the C-6 of a side chain mannose and another glycosidically bound carbohydrate. Mild acid hydrolysis cleaved the phosphate diester linkages to yield mono- and oligosaccharide fractions. Chemical analysis and 1H-NMR studies demonstrated the heterogeneity of the oligosaccharide fractions containing alpha(1,2)-, alpha(1,3)- and alpha(1,6)-linked manno-oligosaccharides. All repeated PPM preparations contained mono-, tri- and heptasaccharides as the phosphate bound main compounds. Galactose, arabinose, fucose, and rhamnose of the monosaccharide fraction and tetra-, penta- and hexasaccharides were not found in all preparations.

Candida↗
PubMed1998

Purine nucleoside phosphorylase: its use in a spectroscopic assay for inorganic phosphate and for removing inorganic phosphate with the aid of phosphodeoxyribomutase.

The kinetics of the phosphorolysis of 7-methylated guanosine analogues catalyzed by purine nucleoside phosphorylase has been analyzed to understand the use of this system as a "Pi mop" to remove Pi from solutions and as a spectroscopic assay for Pi at micromolar concentrations. An expression system was developed for the phosphorylase from Escherichia coli: this protein (subunit molecular mass 26 kDa) and one from a commercial source (29 kDa) were used in this study. Rates of >50 s-1 were obtained for the phosphorolysis at 30 degrees C, so that when the phosphorylase is coupled to the phosphatase being studied, rates of Pi release from the phosphatase can be measured close to this rate. The kinetic mechanism appears to obey the Michaelis-Menten model in the steady state with the bond cleavage rate limiting. Slow hydrolysis of ribose-1-phosphate to Pi catalyzed by the phosphorylase limits the efficiency of the Pi mop. To overcome this, phosphodeoxyribomutase was used to catalyze the conversion of ribose-1-phosphate to ribose-5-phosphate, enabling the Pi mop to remove large amounts of Pi quantitatively. Acyclovir diphosphate provides a simple method to switch off the Pi mop as it is a tight inhibitor (Kd 12 nM) of purine nucleoside phosphorylase.

Acyclovir↗
PubMed1993

Pentose-phosphate pathway in Saccharomyces cerevisiae: analysis of deletion mutants for transketolase, transaldolase, and glucose 6-phosphate dehydrogenase.

Deletion mutants for the yeast transketolase gene TKL1 were constructed by gene replacement. Transketolase activity was below the level of detection in mutant crude extracts. Transketolase protein could be detected as a single protein band of the expected size by Western-blot analysis in wild-type strains but not in the deletion mutant. Deletion of TKL1 led to a reduced but distinct growth in synthetic medium without an aromatic amino-acid supplement. We also isolated double and triple mutants for transketolase (tkl1), transaldolase (tal1), and glucose 6-phosphate dehydrogenase (zwf1) by crossing the different mutants. A tal1 tkl1 double mutant grew nearly like wild-type in rich medium. Only the tkl1 zwf1 double and the tal1 tkl1 zwf1 triple mutant grew more slowly than the wild-type in rich medium. This growth defect could be partly alleviated by the addition of xylulose but not ribose. The triple mutant still grew slowly on a synthetic mineral salts medium without a supplement of aromatic amino acids. This suggests the existence of an alternative but limited source of pentose phosphates and erythrose 4-phosphate in the tkl1 zwf1 double mutants. Hybridization with low stringency showed the existence of a sequence with homology to transketolase, possibly a second gene.

Base Sequence↗
PubMed1978

Maximal reabsorptive capacity for inorganic phosphate (TmPi) in the absence of parathyroid hormone in the rat: decrease of the TmPi during prolonged administration of phosphate and the role of calcium.

Clearance titration studies were performed to examine the maximal reabsorptive capacity for inorganic phosphate (TmPi) in acutely parathyroidectomized (PTX) rats. Under control conditions, the reabsorption of Pi was 6.01 +/- 0.92mumol/min (mean +/- S.D.), and during the administration of phosphate the reabsorption of Pi increased initially to 11.62 +/- 2.20 and decreased finally to 7.97 +/- 2.02mumol/min. The Reabs/GFR values were 2.12 +/- 0.23 (control), 3.57 +/- 0.21 and 2.49 +/- 0.42mumol/ml (experimental), respectively. Thus, the TmPi decreased significantly during phosphate loading. Because this drop of the TmPi was accompanied by a significant decrease of the calcium concentration in plasma in these PTX animals, another series of experiments was performed in which the calcium losses in plasma were replaced. Under these conditions the decrease of the TMPi was significantly smaller than in hypocalcemia. It is concluded that calcium may regulate the renal Pi transport in the absence of parathyroid hormones, at least in hypo- and normocalcemic states.

Animals↗
PubMed1975

Precipitation of calcium phosphates from electrolyte solutions. III. Radiometric studies of the kinetics of precipitation and aging of calcium phosphates.

Precipitation and precipitate transformation in the system sodium phosphate (pre-adjusted to pH 7.4)--calcium chloride (25 degrees) was studied by means of radiometric analysis using 45Ca and 32P as tracers. Changes in the pH and the total concentrations of calcium and phosphate were followed during solid phase formation and the data were used to calculate composition changes of the precipitates and their supernatants. In all investigated systems two-step precipitation was observed, the precursor being more basic than the secondary precipitate. The composition of the latter was mostly within the range of the composition of octacalcium phosphate. The course of further chemical changes was dependent on the pH established during secondary precipitation. The heterogeneous exchange of the radionuclides between the solid phase and their supernatant solutions was also followed as a function of time. The results indicate that recrystallization through the mother liquid accompanied by composition changes is the dominant mechanism of equilibrium of the solid phases.

Apatites↗
PubMedDate not supplied

Modeling of the actomyosin ATPase activity. Origin of the initial phosphate burst and implications of the phosphate release kinetics.

In the rapid "quench" kinetics of myosin, the "initial phosphate burst" is the excess inorganic phosphate that is produced during the early time-course of ATP hydrolysis by myosin subfragment-1 (S-1) or HMM. In general, the existence of a Pi burst implies a rapid (i.e., generally an order of magnitude faster than the steady-state hydrolysis rate) lysis of the phospho-anhydride bond within the ATP molecule, followed by one or more slower steps that are rate limiting for the process. Thus, the presence of a Pi burst can provide an important clue to the mechanism of the reaction. However, in the case of actomyosin, this clue has long been the subject of controversy and misunderstanding. To measure the (initial) Pi burst, myosin S-1 (or HMM) is rapidly mixed with ATP and then the mixture is acid quenched after a specific time period. The medium produced contains free Pi generated from hydrolysis of the ATP. The quantitative measure of the phosphate generated in this way has always been significantly greater than that expected by steady-state "release" of Pi alone, and it is that very difference between this measured Pi after the quench and that amount of Pi expected to be released by steady-state considerations in that same time period that has been referred to as the "initial Pi burst." Recent investigations of the kinetics of Pi release have used an entirely new method that directly measures the release of Pi from the enzyme-product complex. These studies have made reference to the properties of the "initial Pi burst" in the presence of actin, as well as to a new kinetic entity: the "burst of Pi release," and have been often vague concerning the true nature of the initial Pi burst, as well as the properties of Pi release as predicted by the current models of the actin activation of the myosin ATPase activity. The purpose of the current article is to correct this oversight, to discuss the "burst" in some detail, and to display the kinetics predicted by the current models for the actin activation of myosin. Furthermore, predictions for the kinetics of the new "burst of Pi release" are discussed in terms of its ability to discriminate between the two current competing models for actin activation of the myosin ATPase activity.

Actins↗
PubMed1983

Determination of protein-bound phosphate by continuous flow analysis: automated procedure for the determination of alkali-labile phosphate.

A method is described for the specific, quantitative determination of protein-bound phosphorus by a continuous flow procedure using a Technicon AutoAnalyzer. It is based on the exceptional alkali lability of serine phosphate linkages to beta-elimination when the serine residues are present in a polypeptide chain. The results are reproducible within about 3, 5, or 10%, respectively, when the analytical sample contains about 100, 10, or 3 nmol of protein-bound P. The presence of less than 1 nmol protein-bound P can be detected. The method tolerates wide variations of the pH and ionic composition of the sample, making it suitable for the automatic, serial analysis of chromatographic effluent fractions. Low-molecular-weight phosphomonoesters, ribonucleic acid (phosphodiester), and nucleotide phosphates (pyrophosphate) do not react measurably. Carboxyphenyl phosphate is partially hydrolyzed (10-15%). In contrast, the release of P from various phosphoproteins is quantitative.

Alkalies↗
PubMed1986

Stimulation by dolichol phosphate-mannose of N-acetylglucosaminyl-lipid biosynthesis by membranes from class E Thy-1-negative mutant mouse lymphoma cells which are defective in dolichol phosphate-mannose biosynthesis.

Dolichol phosphate-mannose has been shown previously to stimulate the biosynthesis of N-acetylglucosaminyl-diphosphate-dolichol (E. L. Kean (1985) J. Biol. Chem. 260, 12561-12571). Although the class E Thy-1-negative mutant mouse lymphoma cells are unable to synthesize dolichol phosphate-mannose, the addition of this compound exogenously to membranes from the mutant cells brought about a stimulation of N-acetylglucosaminyl-lipid synthesis similar to that obtained with membranes from wild type cells. The retention of this activity by the mutant cells supports the suggestion of a regulatory role for dolichol phosphate-mannose as an intrinsic property of the glucosaminyltransferase which catalyzes the initial reaction of the dolichol pathway.

Acetylglucosamine↗
PubMed1980

Studies on (Na+ + K+)-activated ATPase. XLIV. Single phosphate incorporation during dual phosphorylation by inorganic phosphate and adenosine triphosphate.

(Na+ + K+)-ATPase can be phosphorylated by its substrate ATP as well as by its product inorganic phosphate. The maximal capacity for phosphorylation by either of these two substances is one mol phosphate per mol enzyme. In order to investigate whether the enzyme molecule possesses only on phosphorylation site common to ATP and Pi, or two phosphorylation sites, one for ATP and one for Pi, dual phosphorylation of the enzyme has been carried out. Under conditions, which are maximally favourable for each type of phosphorylation, successive phosphorylation by Pi and ATP leads to a maximal incorporation of only one mol phosphate per mol enzyme. The phosphorylation capacity for ATP decreases by the same amount as the Pi-phosphorylation level increases, without an effect on the apparent affinity for ATP. The results can be explained by assuming either a single common phosphorylation site for Pi and ATP, or a conformational change of the enzyme following phosphorylation by Pi, which excludes phosphorylation by ATP.

Adenosine Triphosphate↗
PubMed1980

Nucleation-controlled aggregation of deoxyhemoglobin S. Effect of organic phosphates on the kinetics of aggregation of deoxyhemoglobin S in concentrated phosphate buffer.

The kinetics of the aggregatin of deoxyhemoglobin S in concentrated phosphate buffer were studied turbidimetrically in the presence of organic phosphates. The addition of inositol hexsphosphate shortened the delay time by 35-80%, the range depending on the hemoglobin concentration. The logarithmic plot of delay time versus hemoglobin concentration in 1.85 M potassium phosphate buffer, pH 7.34, showed a linear relationship with a slope (n value) of 2.5 +/- 0.14 in the absence of inositol hexaphosphate, while the slope was decreased to 2.1 in the presence of inositol hexaphosphate. The turbidity (A700) of aggregates per g deoxy Hb S was found to be lower in the presence of inositol hexaphosphate than in the absence of inositol hexaphosphate. The solubility of deoxy Hb S was decreased by inositol hexaphosphate. 2,3-Diphosphoglyceric acid also showed an effect similar to that of inositol hexaphosphate. However, if the pentacyclohexylammonium salt of diphosphoglyceric acid were used, the delay time was increased significantly. The opposite effect of the pentacyclohexylammonium salt of diphosphoglyceric acid on the delay time was found to be attributed to the anti-gelation effect of the pentacyclohexoxylammonium ion. The difference in the effect of inositol hexaphosphate and diphosphoglyceric acid on the delay time appears to be related to their effect on the solubility of deoxy Hb S.

Diphosphoglyceric Acids↗
PubMed1989

Formation of directly mutagenic alpha-hydroxy-N-nitrosopiperidine phosphate ester by near-ultraviolet irradiation of N-nitrosopiperidine in phosphate buffer.

Previously we found that direct-acting mutagens can be formed from N-nitrosodialkylamines on exposure to near-ultraviolet light in the presence of phosphates. We have now isolated the mutagenic photoproduct formed from N-nitrosopiperidine and inorganic phosphate and identified its structure as the phosphate ester of alpha-hydroxy-N-nitrosopiperidine. This reaction represents a new, non-enzymatic activation of promutagenic N-nitrosodialkylamines.

Buffers↗
PubMed1978

Effect of racemic and S(+) alpha-chlorohydrin-1-phosphate on glyceraldehyde-3-phosphate dehydrogenase in relation to its contraceptive action.

The phosphate esters of racemic (+/-) alpha-chlorohydrin and its S(+)-optical isomer have been prepared as cyclohexylamine salts. In vitro both inhibited glyceraldehyde-3-phosphate dehydrogenase by a competitive mechanism, whereas (+/-) alpha-chlorohydrin did not. The S(+)-isomer was approximately four times as potent as the racemate. These results correlate with data concerning the relative contraceptive activity in rats of racemic and S(+) alpha-chlorohydrin. They support the view that the antifertility mechanism involves in vivo formation of S(+) alpha-chlorohydrin-1-phosphate, with resulting inhibition of glycolysis in sperm.

Animals↗
PubMed1993

Sucrose-phosphate synthase phosphatase, a type 2A protein phosphatase, changes its sensitivity towards inhibition by inorganic phosphate in spinach leaves.

The activity of a type 2A protein phosphatase from spinach leaves was monitored using phosphorylated sucrose-phosphate synthase (SPS) as a substrate. After partial purification the overall activities of sucrose-phosphate synthase phosphatase (SPS-P) recovered from leaves harvested in the dark and in the light did not vary. However, SPS-P preparations from darkened leaves were more strongly inhibited by inorganic phosphate and certain phosphorylated compounds than preparations from illuminated or mannose fed leaves. We conclude, that activation of SPS involves an interconversion of multiple forms of SPS-P activity.

Catalysis↗
PubMed1985

Activities of L-lactate and glycerol phosphate production rates in vitro from glucose 6-phosphate in regenerating rat liver.

Activities of L-lactate and glycerol phosphate production in vitro were assayed in regenerating rat liver at different times after partial hepatectomy and were compared with activities of sham operated controls. Results show an oscillatory shift in these activities with smallest values for both L-lactate and glycerol phosphate production rates at 20 hr, these being 80% and 50%, respectively of normal values, and with highest values at 42 hr where these rates were 150% and 125%, respectively, both recovering their original state 60 hr after surgery. From these data it is concluded that in regenerating liver there are changes in the ability of the glycolysis system to produce L-lactate and glycerol phosphate.

Animals↗
PubMed1994

On the photochemical release of phosphate from 3,5-dinitrophenyl phosphate in a protein crystal.

In time-resolved diffraction studies, reaction initiation should ideally be both uniform throughout the body of the crystal and rapid with respect to the reaction under study. Caged compounds have been used in a number of experiments to provide photochemical initiation of catalytic reactions in enzyme crystals. No in situ measurements have been reported so far on the kinetics of photolysis or on the distribution of photolysis products within crystals. With the aid of a fast single-crystal microspectrophotometer, we performed quantitative studies on the photolysis of a caged compound, 3,5-dinitrophenyl phosphate, in crystals of glycogen phosphorylase b. The results show that for concentrations required in kinetic experiments, the photolytic release of phosphate from 3,5-dinitrophenyl phosphate is restricted to a thin surface layer only. The liberated substrate is then transported by diffusion into the body of the crystal. In effect, the speed of reaction initiation is limited by the rate of diffusion rather than by the rate of the photochemical reaction. The paper discusses general criteria and experimental strategies for the successful use of photoreactive protective groups in time-resolved diffraction experiments.

Crystallization↗