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PubMed1991

Binding of sugar phosphates, inositol phosphates and phosphorylated amino acids to actin.

Binding of biological phosphate compounds to actin was investigated by the effect of these compounds on the critical concentration of the pointed ends of gelsolin-capped actin filaments. According to this assay millimolar concentrations of glucose 6-phosphate and the bisphosphorylated sugars fructose 1,6-bisphosphate, fructose 2,6-bisphosphate, glucose 1,6-bisphosphate, sedoheptulose 1,7-bisphosphate and 2,3-bisphosphoglycerate were found to associate with actin. Glycerophosphoinositol phosphates bound to actin if they were present in millimolar concentrations, and if carbon atom 4 of the inositol ring was phosphorylated and carbon atom 5 was free of phosphate. Also phosphoserine and phosphotyrosine were found to interact with actin. Most of the actin-binding compounds stabilized actin filaments by decreasing the critical concentration suggesting that these compounds had a higher affinity for the subunits along actin filaments than for actin monomers. However, 2,3-bisphosphoglycerate and fructose 2,6-bisphosphate increased the critical concentration probably because these sugar phosphates bound to actin monomers thereby inhibiting actin polymerization.

Actins↗
PubMed2002

A phosphate-stimulated NAD(P)+-dependent glyceraldehyde-3-phosphate dehydrogenase in Bacillus cereus.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme of central carbon metabolism, was studied in a Bacillus cereus strain isolated from the phosphate layer from Morocco. Enzymatic assays with cell extracts demonstrated that when grown on Luria-Bertani (LB) medium, B. cereus contains a major NAD+-dependent GAPDH activity and only traces of NADP+-dependent activity, but in cells grown on Pi-supplemented LB medium a strong increase of the NADP+-dependent activity, that became predominant, occurs concurrently with a GAPDH protein increase. Our results show that B. cereus possesses two GAPDH activities, namely NAD+- and NADP+-dependent, catalyzed by two enzymes with distinct coenzyme specificity and different phosphate regulation patterns. The finding of a phosphate-stimulated NADP+-dependent GAPDH in B. cereus indicates that this bacterium can modulate its primary carbon metabolism according to phosphate availability.

Bacillus cereus↗
PubMed2005

CpsE from type 2 Streptococcus pneumoniae catalyzes the reversible addition of glucose-1-phosphate to a polyprenyl phosphate acceptor, initiating type 2 capsule repeat unit formation.

The majority of the 90 capsule types made by the gram-positive pathogen Streptococcus pneumoniae are assembled by a block-type mechanism similar to that utilized by the Wzy-dependent O antigens and capsules of gram-negative bacteria. In this mechanism, initiation of repeat unit formation occurs by the transfer of a sugar to a lipid acceptor. In S. pneumoniae, this step is catalyzed by CpsE, a protein conserved among the majority of capsule types. Membranes from S. pneumoniae type 2 strain D39 and Escherichia coli containing recombinant Cps2E catalyzed incorporation of [14C]Glc from UDP-[14C]Glc into a lipid fraction in a Cps2E-dependent manner. The Cps2E-dependent glycolipid product from both membranes was sensitive to mild acid hydrolysis, suggesting that Cps2E was catalyzing the formation of a polyprenyl pyrophosphate Glc. Addition of exogenous polyprenyl phosphates ranging in size from 35 to 105 carbons to D39 and E. coli membranes stimulated Cps2E activity. The stimulation was due, in part, to utilization of the exogenous polyprenyl phosphates as an acceptor. The glycolipid product synthesized in the absence of exogenous polyprenyl phosphates comigrated with a 60-carbon polyprenyl pyrophosphate Glc. When 10 or 100 microM UMP was added to reaction mixtures containing D39 membranes, Cps2E activity was inhibited 40% and 80%, respectively. UMP, which acted as a competitive inhibitor of UDP-Glc, also stimulated Cps2E to catalyze the reverse reaction, with synthesis of UDP-Glc from the polyprenyl pyrophosphate Glc. These data indicated that Cps2E was catalyzing the addition of Glc-1-P to a polyprenyl phosphate acceptor, likely undecaprenyl phosphate.

Bacterial Capsules↗
PubMed1990

Mitochondrial phosphate transport. N-ethylmaleimide insensitivity correlates with absence of beef heart-like Cys42 from the Saccharomyces cerevisiae phosphate transport protein.

The mitochondrial phosphate transport protein (PTP) has been purified in a reconstitutively active form from Saccharomyces cerevisiae and Candida parapsilosis. ADP/ATP carriers that copurify have been identified. The PTP from S. cerevisiae migrates as a single band (35 kDa) in sodium dodecyl sulfate gels with the same mobility as the N-ethylmaleimide-alkylated beef heart PTP. It does not cross-react with anti-sera against beef heart PTP. The CNBr peptide maps of the yeast and beef proteins are very different. The rate of unidirectional phosphate uptake into reconstituted proteoliposomes is stimulated about 2.5-fold to a Vmax of 170 mumol of phosphate min-1 (mg PTP)-1 (22 degrees C) by increasing the pHi of the proteoliposomes from 6.8 (same as pHe) to 8.0. The Km for Pi of this reconstituted activity is 2.2 mM. The transport is sensitive to mersalyl (50% inhibition at 60 microM) and insensitive to N-ethylmaleimide. We have purified peptides matching the highly conserved motif Pro-X-(Asp/glu)-X-X-(Lys/Arg)-X-(Arg/lys) (X is an unspecified amino acid) of the triplicate gene structure sequence of the beef heart PTP. The N-ethylmaleimide-reactive Cys42 of the beef heart protein, located between the two basic amino acids of this motif (Lys41-Cys42-Arg43), is replaced with a Thr in the yeast protein. This substitution most likely is responsible for the lack of N-ethylmaleimide sensitivity of the yeast protein and mersalyl thus reacts with another cysteine to inhibit the transport. Finally it is concluded that Cys42 has no essential role in the catalysis of inorganic phosphate transport by the mitochondrial phosphate transport protein.

Amino Acid Sequence↗
PubMed1985

Elevated phosphate transporting activity and phosphate carrier content in mitochondria of rat hepatoma with high glycolytic capacity.

Transport of inorganic phosphate into Zajdela hepatoma mitochondria proceeds with approximately the same Km and about two times higher Vmax than the transport into mitochondria of rat liver. As detected by (a) titration of the inhibition of mitochondrial phosphate-stimulated respiration and phosphate-induced swelling by mersalyl and (b) binding of /14C/-NEM and /14C/-DCCD to a 33 kDa protein in mitochondria, the higher phosphate transporting activity of the hepatoma mitochondria is due to about a three fold increase in phosphate carrier content in the tumor mitochondria.

Animals↗
PubMed1983

Crystal populations in human synovial fluid. Identification of apatite, octacalcium phosphate, and tricalcium phosphate.

Defatted joint fluid pellets from 4 patients with the "Milwaukee shoulder" syndrome, an aspirate of milky fluid from subcutaneous tissue of a girl with dermatomyositis/calcinosis, and 2 rabbit synovial membranes calcified by calciphylaxis were studied by Fourier transform infrared analysis. This method permits sequential electronic subtraction ("stripping") of known patterns of highly characterized reference compounds from an unknown sample pattern. Collagen and hydroxyapatite, with carbonate partially (1-3%) substituted for phosphate, and to a lesser extent hydroxyl, were found in all samples. Octacalcium phosphate (OCP) was found in all samples except that from a patient with synovial chondromatosis which contained tricalcium phosphate (TCP). Sulfate was found in 2 of the shoulder joint fluid specimens. An unidentified organic phase was present in all samples. This study confirms recent observations by others that pathologic calcifications contain several mineral phases. These data raise the possibility that hydroxyapatite nucleation may be controlled by hydrolytic alteration of precursor calcium phosphate phases such as OCP or TCP. Studies of the biologic effects of synthetic calcium phosphate crystals must take into account the existence of several crystalline phases in natural pathologic calcifications.

Animals↗
PubMed1995

Effect of particle size of metastable calcium phosphates on mechanical strength of a novel self-setting bioactive calcium phosphate cement.

Resistance to compressive strength after setting of the calcium phosphate cement consisting of tetracalcium phosphate (TECP), dicalcium phosphate dihydrate (DCPD), and 40 wt/wt% of a synthetic hydroxyapatite (HAP) was tested. An equimolar mixture of the calcium phosphate powder containing DCPD (particle diameter [D] 0.52-3.33 microns) and TECP (D, 1.1-13.1 microns) transformed into HAP at 37 degrees C, 100% RH after being mixed with 25 mM phosphoric acid. X-ray diffraction suggested that the cement containing fine particles of DCPD and TECP completely transformed to HAP, but that mixtures containing larger particles did not. Because particle size of both DCPD and TECP affected the compressive strength of the cement, the crystal growth of HAP during cement formation depended on the specific surface area (Sw) of the raw materials. The crystallite size of transformed HAP was estimated based on X-ray diffraction peaks at 25.8 and 32.8 degrees attributable to the 002 and 300 planes. The crystalline size attributable to the 300 plane decreased with increasing Sw, but that attributable to the 002 plane showed no significant relationship. The compressive strength of the cement after hardening increased with an increase of its Sw. This suggested that the harder calcium phosphate cement was (derived) from the smaller particle size of the raw materials.

Bone Cements↗
PubMed2004

Effect of rapidly resorbable calcium phosphates and a calcium phosphate bone cement on the expression of bone-related genes and proteins in vitro.

The use of biodegradable bone substitutes is advantageous for alveolar ridge augmentation because it avoids second-site surgery for autograft harvesting. This study examines the effect of novel, rapidly resorbable calcium phosphates and a calcium phosphate bone cement on the expression of bone-related genes and proteins by human bone-derived cells (HBDCs) and compares this behavior to that of tricalciumphosphate (TCP). Test materials were alpha-TCP, two materials with a crystalline phase Ca(2)KNa(PO(4))(2) and with a small amorphous portion containing either magnesium potassium phosphate (material denominated GB14) or silica phosphate (material denominated GB9), and a calcium phosphate bone cement (material denominated Biocement D). HBDCs were grown on the substrata for 3, 7, 14, and 21 days, counted, and probed for various mRNAs and proteins (type I collagen, osteocalcin, osteopontin, osteonectin, alkaline phosphatase, and bone sialoprotein). All substrates supported continuous cellular growth for 21 days. In the presence of GB14 and Biocement D specimens cell proliferation was reduced and cell differentiation increased. At day 21, the greatest number of cells was found on GB9 expressing significantly higher levels of bone-related proteins than cells grown on all other surfaces. Because all novel materials facilitated the expression of the osteoblastic phenotype at least as much as TCP and the polystyrene control, these biomaterials can be regarded as excellent candidate bone substitute materials. GB9 induced the highest proliferation and cellular differentiation after 21 days of incubation, suggesting that this material may possess a higher potency for enhancing osteogenesis than TCP.

Adolescent↗
PubMed1985

Influence of inorganic phosphate on the lipid synthesis of a phosphate-deregulated mutant of Streptomyces noursei.

Phosphate-dependent changes of the mycelial lipid composition were studied in the streptothricin-producing parental strain Streptomyces noursei JA 3890 b/2 and its mutant RG 2. In contrast to its ancestor, the mutant was capable of producing the antibiotic nourseothricin even when large quantities of inorganic phosphate were present in the medium. The apparent insensitivity of the secondary metabolism to phosphate inhibition corresponds to a decreased level of phospholipids in the presence of excessive inorganic phosphate and, during phosphate limitation, to a much higher production of the alkaline phosphatases. A model is discussed which proposed the control by a common genetic element of both the phospholipid and antibiotic production.

Alkaline Phosphatase↗
PubMed1998

Substrates of hexokinase, glucose-6-phosphate dehydrogenase, and glyceraldehyde-3-phosphate dehydrogenase prevent the inhibitory response induced by ascorbic acid/iron and dehydroascorbic acid in rabbit erythrocytes.

Exposure of intact rabbit erythrocytes or erythrocyte lysates to ascorbic acid/FeCl3 in a glucose-free saline promoted a rapid decline in reduced glutathione and this response was paralleled by inactivation of hexokinase. Under the same conditions, the activity of the enzymes glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase did not show appreciablevariations in intact cells, but was severely inhibited in the cell-free system. Similar results were obtained by replacing ascorbic acid/FeCl3 with dehydroascorbic acid. In addition, both treatments effectively inhibited the activity of purified hexokinase as well as those of glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. Further studies using the cell-free system indicated that the inhibition of enzyme activities elicited by either of the two treatments was effectively counteracted by the specific substrates of these enzymes. The fact that the hexokinase substrate glucose freely permeates the plasma membrane, unlike the substrates of glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphatedehydrogenase, explains the selective inhibition of hexokinase observed in intact cells. The above results also indicate that dehydroascorbic acid is an inhibitor of these enzymes and strongly suggest that it is at least in part responsible for the effects mediated by the cocktail ascorbic acid/FeCl3.

Animals↗
PubMed1993

Pathogenesis of cholesteryl lipidosis of adrenocortical and ovarian interstitial cells in F344 rats caused by tricresyl phosphate and butylated triphenyl phosphate.

Triaryl phosphates including tricresyl phosphate (TCP) and butylated triphenyl phosphate (BTP) are organophosphates used in the commercial manufacture of plastics, lubricants, and hydraulic fluids. Rat steroidogenic tissues such as adrenocortical (AC), ovarian interstitial (OI), and Leydig cells use an intracellular pathway to store cholesterol (substrate for biosynthesis of steroid hormones) as cholesteryl ester (CE). This pathway and the pathway for uptake of serum cholesterol are less used in Leydig cells of the adult male rat, resulting in a lower CE pool. BTP and TCP caused cholesteryl lipidosis in steroid hormone-synthesizing AC and OI, but not Leydig cells in the adult rat. The objectives of this study were to determine if the administration of triaryl phosphate fluids caused a defect in the cholesterol storage pathway of AC and OI cells and to determine the mechanism of action. Female rats received daily oral doses of 0 or 0.4 g/kg TCP in sesame oil vehicle or 1.7 g/kg neat BTP for 40 days. Adrenal glands from both treatment groups and ovaries from TCP-treated rats were heavier than controls. Microscopic and biochemical studies revealed cholesteryl lipidosis composed of CE in the adrenal glands and ovaries in BTP- and TCP-treated rats with the latter group affected most severely. The activity of neutral CE hydrolase (nCEH), an enzyme that converts CE to cholesterol in the uptake and storage pathways, also was inhibited most in the TCP-treated group (97% inhibition compared to that of control). The activity of acyl coenzyme A:cholesterol acyl transferase, an enzyme that esterifies cholesterol to make CE, was depressed 27% compared to that of control adrenal glands of the TCP group, resulting in elevated intracellular cholesterol levels in AC cells. An inhibition of nCEH in the storage and uptake pathways by triaryl phosphates most likely resulted in the striking accumulation of CE in cytoplasmic lipid droplets of AC and OI cells in F344 rats.

Adrenal Cortex Diseases↗
PubMed1991

Solid state 31NMR studies of the conversion of amorphous tricalcium phosphate to apatitic tricalcium phosphate.

The hydrolytic conversion of a solid amorphous calcium phosphate of empirical formula Ca9 (PO4)6 to a poorly crystalline apatitic phase, under conditions where Ca2+ and PO4(3-) were conserved, was studied by means of solid-state magic-angle sample spinning 31P-NMR (nuclear magnetic resonance). Results showed a gradual decrease in hydrated amorphous calcium phosphate and the formation of two new PO4(3-)-containing components: an apatitic component similar to poorly crystalline hydroxyapatite and a protonated PO4(3-), probably HPO4(2-) in a dicalcium phosphate dihydrate (DCPD) brushite-like configuration. This latter component resembles the brushite-like HPO4(2-) component previously observed by 31P-NMR in apatitic calcium phosphates of biological origin. Results were consistent with previous studies by Heughebaert and Montel [18] of the kinetics of the conversion of amorphous calcium phosphate to hydroxyapatite under the same conditions.

Apatites↗
PubMed2003

Phosphate ions in bone: identification of a calcium-organic phosphate complex by 31P solid-state NMR spectroscopy at early stages of mineralization.

Previous 31P cross-polarization and differential cross-polarization magic angle spinning (CP/MAS and DCP/MAS) solid-state NMR spectroscopy studies of native bone and of the isolated crystals of the calcified matrix synthesized by osteoblasts in cell culture identified and characterized the major PO(-3)(4) phosphate components of the mineral phase. The isotropic and anisotropic chemical shift parameters of the minor HPO(-2)(4) component in bone mineral and in mineral deposited in osteoblast cell cultures were found to differ significantly from those of brushite, octacalcium phosphate, and other synthetic calcium phosphates. However, because of in vivo and in vitro evidence that phosphoproteins may play a significant role in the nucleation of the solid mineral phase of calcium phosphate in bone and other vertebrate calcified tissues, the focus of the current solid-state 31P NMR experiments was to detect the possible presence of and characterize the phosphoryl groups of phosphoproteins in bone at the very earliest stages of bone mineralization, as well as the possible presence of calcium-phosphoprotein complexes. The present study demonstrates that by far the major phosphate components identified by solid-state 31P NMR in the very earliest stages of mineralization are protein phosphoryl groups which are not complexed with calcium. However, very small amounts of calcium-complexed protein phosphoryl groups as well as even smaller, trace amounts of apatite crystals were also present at the earliest phases of mineralization. These data support the hypothesis that phosphoproteins complexed with calcium play a significant role in the initiation of bone calcification.

Animals↗
PubMed2006

Effects of phosphates on the expression of tissue-nonspecific alkaline phosphatase gene and phosphate-regulating genes in short-term cultures of human osteosarcoma cell lines.

We studied the effects of phosphates on the expression of the human tissue-nonspecific alkaline phosphatase (TNSALP) gene and phosphate-regulating genes in short-term cultures of human osteoblastic osteosarcoma cell lines. When human osteosarcoma cell lines, SaOS-2, MG-63, and U(2)OS were cultured with 10 mM inorganic sodium dihydrogenphosphate, 10 mM beta-glycerophosphate, 250 microM pyridoxal phosphate, or 100 microM inorganic pyrophosphate, enzymatic activity of alkaline phosphatase began to increase at 72 h after addition of sodium dihydrogenphosphate and beta-glycerophosphate in SaOS-2 cells. Pyridoxal phosphate and pyrophosphate did not induce alkaline phosphatase activity. U(2)OS cells slightly reacted to beta-glycerophosphate, but MG-63 cells did not react on exposure to phosphates. In SaOS-2 cells, TNSALP mRNA measured by real-time RT-PCR reached a peak level at 72 h after the addition of beta-glycerophosphate. PHEX and MEPE mRNAs were also induced by beta-glycerophosphate. These results suggest that TNSALP, PHEX and MEPE were concordantly induced by beta-glycerophosphate on mineralisation.

Alkaline Phosphatase↗
PubMed1991

Net phosphate transport in phosphate-starved Candida utilis: relationships with pH and K+.

Phosphate transport was studied in phosphate-starved Candida utilis using 31P-NMR and in situ pH and K(+)-specific electrodes. A transient efflux of K+ was associated with the initial net influx of orthophosphate across the plasma membrane and decrease of both the plasma membrane pH gradient and the cytosol pH. Recovery of cytosol pH, and the plasma membrane pH gradient after phosphate uptake, was slow when extracellular K+ was depleted, but rapid when K+ was added to the suspension either with orthophosphate or after phosphate uptake. Net phosphate transport into the vacuole occurs against its concentration gradient and is associated with an increase of the tonoplast pH gradient. It is proposed that transport of orthophosphate into the vacuole is mediated by an electrical uniport and driven by the tonoplast membrane potential.

Biological Transport↗
PubMed1976

Specific activities of 6-phosphogluconate dehydrogenase, glucose-6-phosphate dehydrogenase and glucose-6-phosphate isomerase during Bufo bufo development.

It has been suggested by some authors that during amphibian development, due to the higher glucose-6-phosphate dehydrogenase (EC 1.1.1.49) activity compared to that of 6-phosphogluconate dehydrogenase (EC 1.1.1.43), 6-phosphogluconate could accumulate in the embryo tissues and regulate the channelling of glucose-6-phosphate into glycolysis. Here, on the base of the specific activities of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and glucose-6-phosphate isomerase (EC 5.3.1.9) found in the embryos of Bufo bufo during development, it is discussed whether 6-phosphogluconate can accumulate and play a regulative role on glucose-6-phosphate metabolism in the anuran embryo.

Animals↗
PubMed1984

The triose-phosphate site of homogeneous reconstituted sn-glycerol-3-phosphate acyltransferase of Escherichia coli.

The sn-glycerol-3-phosphate (glycerol-phosphate) acyltransferase of Escherichia coli was purified to near homogeneity and its activity reconstituted with phospholipids (Green, P.R., Merrill, A.M., Jr. and Bell, R.M. (1981) J. Biol. Chem. 256, 11151-11159). The competency of glycerol-P analogues to serve as inhibitors and as substrates was investigated. Dihydroxyacetone-P, ethyleneglycol-P, 1,3-propanediol-P, 3,4-dihydroxybutylphosphonate and DL-glyceraldehyde-3-P were inhibitors of the reconstituted purified glycerol-phosphate acyltransferase. The kinetics of inhibition, while formally of the mixed type, most closely resembled that of a simple competitive inhibition with respect to glycerol-3-P. Inorganic phosphate was also found to be a competitive inhibitor. All of the glycerol-3-P analogues except DL-glyceraldehyde-3-P were substrates. Of these, dihydroxyacetone-P proved to be the best substrate. The secondary hydroxyl was not necessary for activity. Glycerol-phosphate acyltransferase catalyzed the hydrolysis of palmitoyl-CoA in the presence of DL-, but not D-glyceraldehyde-3-P. This suggests that the gem diol of L-glyceraldehyde-3-P may be a substrate, and that the acylated adduct may be unstable. The enzyme was inactivated by phenylglyoxal and butanedione, suggesting that arginine may be at or near the active site.

Acyltransferases↗
PubMed1992

Inhibition of glycerol-3-phosphate acyltransferase by analogs of glycerol-3-phosphate.

Analogs of glycerol-3-phosphate were tested as substrates or inhibitors of the glycerol-3-phosphate acyltransferases of mitochondria and microsomes. (rac)-3,4-Dihydroxybutyl-1-phosphonate, (rac)-glyceraldehyde 3-phosphate, (rac)-3-hydroxy-4-oxobutyl-1-phosphonate, (1S,3S)-1,3,4-trihydroxybutyl-1-phosphonate, and (1R,3S)-1,3,4 trihydroxybutyl-1-phosphonate were competitive inhibitors of both mitochondrial and microsomal sn-glycerol-3-phosphate acyltransferase activity. An isosteric analog of dihydroxyacetone phosphate, 4-hydroxy-3-oxobutyl-1-phosphonate, was a much stronger competitive inhibitor of the microsomal than the mitochondrial enzyme. Phenethyl alcohol was a noncompetitive inhibitor of both the microsomal and the mitochondrial acyltransferases. The product of the mitochondrial acyltransferase reaction with (rac)-3,4-dihydroxybutyl-1- phosphonate was almost exclusively (rac)-4-palmitoyloxy-3-hydroxybutyl-1-phosphonate. The microsomal acylation reaction generated both the monoacyl product and (S)-3,4-dipalmitoyloxybutyl-1-phosphonate. The apparent Km for (S)-3,4-dihydroxybutyl-1-phosphonate was 2.50 and 1.38 mM for the mitochondrial and microsomal enzymes, respectively.

Acylation↗