Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Polyphosphates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed2000

Identification of polyphosphate-accumulating organisms and design of 16S rRNA-directed probes for their detection and quantitation.

Laboratory-scale sequencing batch reactors (SBRs) as models for activated sludge processes were used to study enhanced biological phosphorus removal (EBPR) from wastewater. Enrichment for polyphosphate-accumulating organisms (PAOs) was achieved essentially by increasing the phosphorus concentration in the influent to the SBRs. Fluorescence in situ hybridization (FISH) using domain-, division-, and subdivision-level probes was used to assess the proportions of microorganisms in the sludges. The A sludge, a high-performance P-removing sludge containing 15.1% P in the biomass, was comprised of large clusters of polyphosphate-containing coccobacilli. By FISH, >80% of the A sludge bacteria were beta-2 Proteobacteria arranged in clusters of coccobacilli, strongly suggesting that this group contains a PAO responsible for EBPR. The second dominant group in the A sludge was the Actinobacteria. Clone libraries of PCR-amplified bacterial 16S rRNA genes from three high-performance P-removing sludges were prepared, and clones belonging to the beta-2 Proteobacteria were fully sequenced. A distinctive group of clones (sharing >/=98% sequence identity) related to Rhodocyclus spp. (94 to 97% identity) and Propionibacter pelophilus (95 to 96% identity) was identified as the most likely candidate PAOs. Three probes specific for the highly related candidate PAO group were designed from the sequence data. All three probes specifically bound to the morphologically distinctive clusters of PAOs in the A sludge, exactly coinciding with the beta-2 Proteobacteria probe. Sequential FISH and polyphosphate staining of EBPR sludges clearly demonstrated that PAO probe-binding cells contained polyphosphate. Subsequent PAO probe analyses of a number of sludges with various P removal capacities indicated a strong positive correlation between P removal from the wastewater as determined by sludge P content and number of PAO probe-binding cells. We conclude therefore that an important group of PAOs in EBPR sludges are bacteria closely related to Rhodocyclus and Propionibacter.

Actinobacteria↗
PubMed2004

Copper ions stimulate polyphosphate degradation and phosphate efflux in Acidithiobacillus ferrooxidans.

For some bacteria and algae, it has been proposed that inorganic polyphosphates and transport of metal-phosphate complexes could participate in heavy metal tolerance. To test for this possibility in Acidithiobacillus ferrooxidans, a microorganism with a high level of resistance to heavy metals, the polyphosphate levels were determined when the bacterium was grown in or shifted to the presence of a high copper concentration (100 mM). Under these conditions, cells showed a rapid decrease in polyphosphate levels with a concomitant increase in exopolyphosphatase activity and a stimulation of phosphate efflux. Copper in the range of 1 to 2 microM greatly stimulated exopolyphosphatase activity in cell extracts from A. ferrooxidans. The same was seen to a lesser extent with cadmium and zinc. Bioinformatic analysis of the available A. ferrooxidans ATCC 23270 genomic sequence did not show a putative pit gene for phosphate efflux but rather an open reading frame similar in primary and secondary structure to that of the Saccharomyces cerevisiae phosphate transporter that is functional at acidic pH (Pho84). Our results support a model for metal detoxification in which heavy metals stimulate polyphosphate hydrolysis and the metal-phosphate complexes formed are transported out of the cell as part of a possibly functional heavy metal tolerance mechanism in A. ferrooxidans.

Acidithiobacillus↗
PubMed2003

Polyphosphate loss promotes SNF/SWI- and Gcn5-dependent mitotic induction of PHO5.

Approximately 800 transcripts in Saccharomyces cerevisiae are cell cycle regulated. The oscillation of approximately 40% of these genes, including a prominent subclass involved in nutrient acquisition, is not understood. To address this problem, we focus on the mitosis-specific activation of the phosphate-responsive promoter, PHO5. We show that the unexpected mitotic induction of the PHO5 acid phosphatase in rich medium requires the transcriptional activators Pho4 and Pho2, the cyclin-dependent kinase inhibitor Pho81, and the chromatin-associated enzymes Gcn5 and Snf2/Swi2. PHO5 mitotic activation is repressed by addition of orthophosphate, which significantly increases cellular polyphosphate. Polyphosphate levels also fluctuate inversely with PHO5 mRNA during the cell cycle, further substantiating an antagonistic link between this phosphate polymer and PHO5 mitotic regulation. Moreover, deletion of PHM3, required for polyphosphate accumulation, leads to premature onset of PHO5 expression, as well as an increased rate, magnitude, and duration of PHO5 activation. Orthophosphate addition, however, represses mitotic PHO5 expression in a phm3delta strain. Thus, polyphosphate per se is not necessary to repress PHO transcription but, when present, replenishes cellular phosphate during nutrient depletion. These results demonstrate a dynamic mechanism of mitotic transcriptional regulation that operates mostly independently of factors that drive progression through the cell cycle.

Adenosine Triphosphatases↗
PubMed2001

Dissolution of calcium pyrophosphate crystals by polyphosphates: an in vitro and ex vivo study.

OBJECTIVE: To determine the dissolving ability (DA) of linear pentasodium tripolyphosphate (PSTP), cyclic trisodium metaphosphate (TSMP), polymeric sodium metaphosphate (SMP) on synthetic crystals of calcium pyrophosphate dihydrate (CPPD) and on crystalline aggregates of menisci from patients with chondrocalcinosis (CC). METHODS: Synthetic CPPD crystals were mixed with phosphate buffered saline (PBS), which contained the different polyphosphates, for one hour at 37 degrees C. The calcified menisci were obtained from the knees of four female patients with CPPD disease who underwent total arthroscopic meniscectomy for degenerative meniscal lesions. Meniscal cryosections and fragments were incubated in SMP (15 mg/ml PBS) at 37 degrees C for one hour and 24 hours, respectively. Histological evaluation on meniscal samples after polyphosphate incubation was carried out by ordinary transmitted light microscopy and polarised light microscopy. The dissolution of CPPD crystals by polyphosphates was assessed by atomic absorption spectroscopy, which determined the amount of calcium liberated from synthetic crystals and meniscal fragments. Cytotoxicity of SMP was evaluated by tetrazolium salt assay and by an ultrastructural study on cultured chondrocytes. RESULTS: SMP and PSTP showed higher DA on CPPD crystals than TSMP. Analysis of the DA values at increasing concentrations of SMP showed that a concentration of 15 mg/ml completely dissolved 2.0 mg CPPD crystals. The solution of meniscal CPPD crystals showed a significant increase of calcium concentration after three hours and 24 hours of SMP incubation (p=0.0001; Kruskal-Wallis analysis of variance) compared with fragments incubated in PBS control solution. Macroscopic and microscopic evaluation of meniscal specimens showed a notable reduction of CPPD deposits. A 50% inhibitory dose on cultured chondrocytes was reached at the maximum concentration of SMP used in this work (15 mg/ml); ultrastructural analysis did not show morphological alterations in the treated cells. CONCLUSION: The results of this study indicate that linear polyphosphates are effective in dissolving both synthetic and ex vivo CPPD crystal aggregates. This suggests a potential therapeutic use for these molecules in the treatment of symptomatic CC.

Aged↗
PubMed1978

Polyphosphate-deficient mutants of Anacystis nidulans.

Polyphosphate-deficient mutants of Anacystis nidulans have been isolated by either ethyl methanesulfonate (EMS) or N-methyl nitrosoguanidine (NTG) mutagenesis and penicillin-enrichment techniques. Mutagenised stock was preincubated in a medium lacking sulfate, then transferred to a phosphate-lacking medium before penicillin treatment. Many single-colony isolates, in contrast to wild-type, show little growth in absence of phosphate, and have altered polyphosphate, and have altered polyphosphate kinase levels indicating that the lesions affect either the activity or the expression of this enzyme. In these same mutants radioactive phosphate incorporation is severely retarded. Electron micrographs confirm the absence of polyphosphate granules in some mutants.

Cyanobacteria↗
PubMed1996

Effect of stunning time and polyphosphates on quality of cooked chicken breast meat.

The objective of this research was to determine effects of stunning duration and polyphosphates on color, pH, and texture of chicken breast meat. Sixty broiler chickens were electrically stunned for 2 to 10 s in 2-s intervals and then slaughtered. Left and right Pectoralis major muscles were excised 1 h post-mortem. The left muscles (treated) were treated with a sodium tripolyphosphate salt solution, and the right muscles (controls) were treated with a salt solution alone. All muscles were cooked to an endpoint temperature of 72 C in a 95 C water bath. Measurements of muscle pH were taken on the meat 1 h post-mortem, after treating, and after cooking. Color values and Warner-Bratzler shear values were evaluated on each cooked meat sample. As stunning time increased, pH increased at 1 h post-mortem but treating with either of the solutions eliminated this trend. Muscle pH also increased upon cooking except in the polyphosphate-treated muscles, because the latter muscles achieved maximum pH prior to cooking. Stunning had no apparent effect on color values of the cooked meat; however, polyphosphate treatment resulted in meat that was darker and less red than controls. Longer stunning times resulted in greater shear values but polyphosphates did not affect Warner-Bratzler results. Taken together, these data suggest that processing variables that affect muscle pH also affect quality attributes.

Animals↗
PubMed1978

[Inorganic polyphosphate metabolism in Staphylococcus aureus and the action on it of antibiotics].

The culure of Staph. aureus in the exponential growth phase contained 14-18 mg/g of dry orthophosphate biomass and 18-22 mg/g of dry acid insoluble polyphosphate biomass. The extracellular extract of the culture had a phosphohydrolase activity with respect to high molecular polyphosphates, tripolyphosphate and pyrophosphate. Penicillin and bacitracin which inhibited the biosynthesis of the cell wall had no effect on the content of polyphosphates and the phosphohydrolase activity of Staph. aureus. Heliomycin which inhibited the biosynthesis of RNA increased the content of polyphosphates by 1.5 times and decreased the content of ATP by 30 per cent in the cells of Staph. aureus.

Adenosine Triphosphate↗
PubMed1982

Fine cytochemical localization of polyphosphates in the yeast Saccharomyces cerevisiae.

A late exponential culture, cultivated in the absence of phosphates, and a similar culture supplied with phosphate (phosphate overcompensation conditions) were prepared from an industrial strain of Saccharomyces cerevisiae. For the cytochemical staining, the cellular phosphates were transformed into polymeric metal-phosphate complexes by Ca2+ and Mg2+ ions, added to the fixative. The fixative contained 3% glutaraldehyde, buffered by 100 mM Tris-HCl to pH 6.0, plus 100 mM MgCl2 and 100 mM CaCl2. Staining with lead acetate was followed by OsO4 post-fixation. In cells cultivated in the absence of phosphates lead deposits were found in vacuoles only. In the late exponential culture the staining was observed on the surface of the plasmalemma, on the membranes of the endoplasmic reticulum, in mitochondria, in the cell nucleus, and in vacuoles. As a rule, extensive polyphosphate deposits (metachromatic granules) were found in vacuoles. Two hours after phosphate overcompensation, a high quantity of polyphosphate as found also in the cell wall, e.g., in the isthmus of budding cells (scar ring), in the secondary septa of mother and daughter cells, and in the growth apex. When divalent cations were omitted from the fixative, the staining of polyphosphates was limited to the cell wall and large vacuolar granules. The results of cytochemical staining were compared with the biochemical analysis of polyphosphate content in the cultures under study.

Cell Membrane↗
PubMed1994

Incorporation of [32P]orthophosphate into inorganic polyphosphates by human granulocytes and other human cell types.

When human peripheral blood granulocytes were metabolically labeled at 37 degrees C with [32P]orthophosphate, inorganic polyphosphates became preferentially radiolabeled. Incorporation of radiolabel into the polymer appeared to be ATP-independent. [32P]Polyphosphate was identified by its (i) characteristic lability to acid hydrolysis, (ii) insolubility in barium acetate (pH 4.5), (iii) conversion to [32P]trimetaphosphate, (iv) hydrolysis to [32P]orthophosphate by an exopolyphosphate (Saccharomyces cerevisiae scPPX1), and (v) conversion to a "phosphate ladder" which co-migrated on a polyacrylamide gel with a synthetic phosphate ladder. Also, indirect evidence suggested that the [32P]polyphosphate was strongly, noncovalently associated with another unknown molecule. Particulate fractions (13,000 x g) from lysates of human granulocytes, skin fibroblasts, HL-60 and SK-N-SH cells, all demonstrated radiolabeling of polyphosphate when incubated at 37 degrees C with [32P]orthophosphate.

Acid Anhydride Hydrolases↗
PubMed2002

Ecto-diadenosine polyphosphates hydrolase activity on human prostasomes.

BACKGROUND: Ecto-diadenosine polyphosphates are ubiquitous compounds with several physiological roles. Ecto-diadenosine polyphosphates hydrolase control their actions by degrading and terminating their signaling. The present work deals with the identification and partial characterization of ecto-diadenosine polyphosphates hydrolase on human prostasomes. METHODS: Reverse-phase and paired-ion HPLC techniques have been used. RESULTS: Prostasomes have an ecto-diadenosine polyphosphates hydrolase that leads to the degradation of several diadenosine compounds. Kinetic parameters of the enzyme show that diadenosine tetraphosphate is the preferred substrate that is further metabolized by the prostasome-ecto-nucleotidases to adenosine. The ecto-enzyme is bound to the prostasome-membranes through a GPI-anchor and is activated by physiological concentration of Ca+2, Mg+2, and Mn+2. Its optimum pH is also in the slightly alkaline physiological range. Human spermatozoa do not possess this hydrolytic activity, but they can acquire it after fusion with prostasomes. CONCLUSIONS: The existence of an enzyme capable of degrading diadenosine compounds and can be transferred to human spermatozoa suggests new physiological implications for the role of prostasomes in fertilization.

Acid Anhydride Hydrolases↗
PubMed1999

High-performance liquid chromatographic assay of the diadenosine polyphosphates in human platelets.

Diadenosine pentaphosphate (Ap5A) and diadenosine hexaphosphate (Ap6A) were recently identified in human platelets and were shown to be important modulators of cardiovascular function. Here we describe an HPLC assay for quantitating Ap3A, Ap4A, Ap5A, and Ap6A contents in human platelets simultaneously. Di(1,N6-ethenoadenosine) hexaphosphate was used as internal standard. The extraction procedure consists of (a) deproteinization, (b) selective concentration of the diadenosine polyphosphates with a boronate affinity chromatography, and (c) desalting prior to the HPLC analysis. The assay was validated by PSD-MALDI-mass spectrometry and by addition of authentic diadenosine polyphosphate to platelet samples. The assay was carried out by an ion-pair reversed-phase perfusion chromatography. In platelets from human blood the following amounts of diadenosine polyphosphates were determined: Ap3A, 192.5 +/- 151.0 nM; Ap4A, 223.8 +/- 172.3 nM; Ap5A, 100.2 +/- 81.1 nM; Ap6A, 32.0 +/- 19.6 nM (mean +/- SD, n = 105). The described assay can be used with less than 20 ml blood and allows quantitation of the diadenosine polyphosphates in the picomole range.

Blood Platelets↗
PubMed1999

Multiple inositol polyphosphate phosphatase: evolution as a distinct group within the histidine phosphatase family and chromosomal localization of the human and mouse genes to chromosomes 10q23 and 19.

Multiple inositol polyphosphate phosphatase is the only enzyme known to hydrolyze the abundant metabolites inositol pentakisphosphate and inositol hexakisphosphate. We have previously demonstrated that the chick homolog of multiple inositol polyphosphate phosphatase, designated HiPER1, has a role in growth plate chondrocyte differentiation. The relationship of these enzymes to intracellular signaling is obscure, and as part of our investigation we have examined the murine ((MMU)Minpp1) and human ((HSA)MINPP1) homologs. Northern blot analysis demonstrated expression of ((MMU)Minpp1 in a variety of mouse tissues, comparable to the expression of other mammalian homologs, but less restricted than the expression of HiPER1 in chick. A purified (MMU)Minpp1 fusion protein cleaved phosphate from inositol (1,3,4,5)-tetrakisphosphate and para-nitrophenyl phosphate. When the presumptive active site histidine was altered to alanine by site-directed mutagenesis, enzyme activity was abolished, confirming the classification of (MMU)Minpp1 as a histidine phosphatase. The amino acid sequences of the murine and human MINPP proteins share >80% identity with the rat enzyme and >56% identity with HiPER1, with conservation of the C-terminal consensus sequence that retains proteins in the endoplasmic reticulum. The intron/exon structure of the mammalian (MMU)Minpp1 and (HSA)MINPP1 genes is also conserved compared to the chick HiPER1 gene. Sequence analysis of plant and fruit fly MINPP homologs supports the hypothesis that the MINPP enzymes constitute a distinct evolutionary group within the histidine phosphatase family. We have mapped (HSA)MINPP1 to human chromosome 10q23 by fluorescence in situ hybridization, YAC screening, and radiation hybrid mapping. This assignment places (HSA)MINPP1 in a region of chromosome 10 that is frequently mutated in human cancers and places (HSA)MINPP1 proximal to the tumor suppressor PTEN, which maps to 10q23.3. Using a radiation hybrid panel, we localized (MMU)Minpp1 to a region of mouse chromosome 19 that includes the murine homolog of Pten. The evolutionary conservation of this novel enzyme within the inositol polyphosphate pathway suggests a significant role for multiple inositol polyphosphate phosphatase throughout higher eukaryotes.

Amino Acid Sequence↗
PubMed1991

Formation of inositol polyphosphates in cultured adrenal chromaffin cells.

Formation of inositol polyphosphates has been characterized in cultured bovine adrenal chromaffin cells in terms of calcium dependency and isomers of inositol polyphosphates. There are two distinct pathways of generation of InsP3. Stimulants such as high K+ induce InsP3 accumulation by a calcium uptake-dependent mechanism. Stimulants such as Ang II induce InsP3 accumulation by a calcium uptake-independent mechanism. Both mechanisms are involved in nicotinic stimulation. These results suggest that calcium entry as well as receptor-mediated mechanisms play a significant role in phosphoinositides hydrolysis through phospholipase C in adrenal chromaffin cells. Nicotinic receptor stimulation induces a rapid and transient increase in Ins(1,4,5)P3 accumulation followed by a slower accumulation of Ins(1,3,4)P3. Moreover, nicotine induces a large and rapid increase in Ins(1,3,4,5,6)P5 accumulation with an extent and time course similar to Ins(1,4,5)P3, which peaks at 15 sec after stimulation. Nicotine also induced Ins(1,3,4,5)P4 and InsP6 accumulation with a slower time course and a lesser magnitude than Ins(1,3,4,5,6)P5. These results indicate that adrenal chromaffin cells possess fine regulation of inositol polyphosphates metabolism and that inositol polyphosphates are involved with the control of cellular function in these cells.

Adrenal Medulla↗
PubMed1995

Effects of diadenosine polyphosphates, ATP and angiotensin II on membrane voltage and membrane conductances of rat mesangial cells.

Diadenosine polyphosphates have been shown to influence renal perfusion pressure. As mesangial cells may contribute to these effects we investigated the effects of diadenosine triphosphate (Ap3A), diadenosine tetraphosphate (Ap4A), diadenosine pentaphosphate (Ap5A) and diadenosine hexaphosphate (Ap6A) on membrane voltage (Vm) and membrane conductance (gm) in mesangial cells (MC) of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats in primary and long-term culture. We applied the patch-clamp technique in the fast-whole-cell configuration to measure Vm and gm. To compare the effects of diadenosine polyphosphates with hitherto known agonists we also tested adenosine 5´-triphosphate (ATP) and angiotensin II (Ang II). As there was no significant difference in the Vm values in MC of WKY (-42 +/- 1 mV, n = 70) and SHR rats (-45 +/- 2 mV, n = 99) as well as in the agonist-induced changes of Vm, all data were pooled. The Vm of all the cells was -44 +/- 1 mV (n = 169) and gm was 15.9 +/- 1.8 nS (n = 141). Ion-exchange experiments showed the presence of a K+ and a non-selective cation conductance in resting MC whereas a Cl- conductance or a Na+-selective conductance could not be observed. Ap3A, Ap4A, Ap5A, AP6A and ATP each at a concentration of 5 micromol/l, led to a significant depolarization of Vm by 5 +/- 2 mV (n = 14), 7 +/- 1 mV (n = 25), 3 +/- 1 mV (n = 23), 2 +/- 1 mV (n = 16), and 14 +/- 2 mV (n = 23), respectively. For Ap4A, the most potent diadenosine polyphosphate, we determined the half-maximally effective concentration (EC50) as 6 micromol/l (n = 5-25), for ATP as 2 micromol/l (n = 9-37), and for Ang II as 8 nmol/l (n = 6-18). Ap4A 100 micromol/l increased gm significantly by 55 +/- 20% (n = 16), 100 micromol/l ATP by 135 +/- 60% (n = 18). The diadenosine polyphosphates examined were able to depolarize Vm (Ang II > ATP > Ap4A > Ap3A > Ap5A > Ap6A) by activation of a Cl- conductance and a non-selective cation conductance, as do ATP or Ang II.

Adenosine↗
PubMed1995

Effects of diadenosine polyphosphates, ATP and angiotensin II on cytosolic Ca2+ activity and contraction of rat mesangial cells.

Diadenosine polyphosphates (Apn A) are known to influence cellular Ca2+ activity ([Ca2+]i) in several cells. Their vasoactive potency has been described in various systems including the kidney. We examined the effects of diadenosine polyphosphates, adenosine 5'-triphosphate (ATP) and angiotensin II (Ang II) on cytosolic Ca2+ activity of mesangial cells (MC) in culture obtained from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. [Ca2+]i was measured as a fluorescence ratio F340/F380 with the fura-2 technique using three excitation wavelengths (340 nm, 360 nm and 380 nm) and a photon counting tube. Resting [Ca2+]i was not significantly different in MC from WKY and SHR rats and was measured as 132 +/- 9 nmol/l (n = 65) and 114 +/- 12 nmol/l (n = 36), respectively. Diadenosine polyphosphates (Ap3A-Ap6A) increased [Ca2+]i transiently with an initial peak and a secondary plateau phase comparable to the effects of ATP or Ang II. Increases in [Ca2+]i induced by all these agonists were not significantly different between MC of WKY and SHR rats. ATP, Ap3A, Ap4A, Ap5A, Ap6A (each 5 micromol/l) increased the fura-2 fluorescence ratio initially by 0.66 +/- 0.09 (n = 33), 0.52 +/- 0.08 (n = 18), 0.25 +/- 0.05 (n = 16), 0.09 +/- 0.06 (n = 7), 0.09 +/- 0.04 (n = 11), respectively. A half-maximal initial increase in the fura-2 fluorescence ratio was reached at 22 nmol/l, 0.9 micromol/l, 2.0 micromol/l and 4.0 micromol/l with Ang II, Ap3A, ATP and Ap4A, respectively. Ap4A (100 micromol/l, n = 18) led to a reversible contraction of MC. Diadenosine polyphosphates increase [Ca2+]i in rat MC, in a similar manner to ATP or Ang II and lead to a contraction of MC, suggesting that these nucleotides are also involved in the control of glomerular haemodynamics.

Adenosine Triphosphate↗
PubMed1976

Role of ATP-glucokinase and polyphosphate glucokinase in Streptomyces aureofaciens.

The activity of ATP-glucokinase and of polyphosphate glucokinase was examined during growth of the actinomycete Streptomyces aureofaciens 8425 under conditions of intense chlortetracycline (CTC) synthesis. ATP-glucokinase was active in the strain only during the logarithmic phase of culture growth; the activity of polyphosphate glucokinase appears only at the end of the logarithmic phase of growth and rises in parallel with the rate of CTC biosynthesis in the stationary phase. During the rise of activity of polyphosphate glucokinase and of CTC biosynthesis the cells accumulate sugar phosphates, mainly glucose-6-phosphate. It appears that the biosynthesis of CTC in Streptomyces aureofaciens takes place at the expense of glycolysis, using up the high-energy phosphate of high-molecular polyphosphates.

Adenosine Triphosphate↗
PubMed1997

Inositol polyphosphates modify the kinetics of a small chloride channel in skeletal muscle sarcoplasmic reticulum.

The actions of D-myo-inositol 1,4,5-trisphosphate (IP3) and D-myo-inositol 1,3,4,5-tetrakisphospate (IP4) on small chloride (SCl) channels from rabbit skeletal muscle sarcoplasmic reticulum are reported. We find that the inositol polyphosphates (6-40 microM) are potent reversible blockers of SCl channels in lipid bilayers at -40 mV with >10(-5) m cis (cytoplasmic) Ca2+ when added to the cis, but not trans, chamber. IP3 or IP4 at 20 microM reduced the mean open time from 89 +/- 16 msec to 11 +/- 2 msec or to 8.0 +/- 1.0 msec respectively, by abolishing the longest time constant component in the open time distribution. Neither IP3 nor IP4 altered the six single-channel conductance levels. The fraction of low conductance events increased approximately 4-fold and the dwell time at the lower conductance levels increased approximately 3-fold. Channel gating was altered so that most transitions were between the closed level and an open level, in contrast to control channels which remained open for long periods with many transitions between the six open levels. The actions of the inositol polyphosphates were: (1) not prevented by 20 microg/ml cis heparin (an IP3 receptor blocker); (2) mimicked by 10 microM cis synthetic inositol polyphosphates, L-chiro-inositol 1,4,6-trisphosphate and L-chiro-inositol 1,4,6-trisphosphorothionate (which do not bind to IP3 receptors); (3) mimicked by cis additions of the polyanions heparin or hepran (20 microg/ml each) and vanadate (500 microM). The results suggest that an interaction between polyanions and SCl channels would allow the channels to be modulated in vivo by inositol polyphosphates.

Animals↗
PubMed1987

Dependence on pH of formation and oxygen affinity of hemoglobin S fibers in the presence and absence of phosphates and polyphosphates.

This paper presents data on the effect of phosphates and polyphosphates on the formation of hemoglobin S fiber, and on the Bohr effect of hemoglobin S samples whose concentration was high enough (near 5 mM) in order to form fibers upon deoxygenation. The experiments were performed in 0.2 M Bistris or Tris buffers at 30 degrees C in the presence and absence of inositol hexakisphosphate and of 2,3-diphosphoglycerate. Alternatively, 0.2 M phosphate buffers were used without addition of effectors. Under these conditions, few fibers were formed in Tris or Bistris buffers, while extensive fiber formation occurred in the presence of phosphates and polyphosphates. In all cases, increasing pH strongly inhibited fiber formation. At pH 7.5 and above, fibers were not formed in our samples. In the presence of phosphates and polyphosphates fiber formation reduced the oxygen affinity of hemoglobin S with respect to either hemoglobin A or soluble hemoglobin S under similar experimental conditions. The fiber-polyphosphate complexes showed a larger Bohr effect than that in hemoglobin A. In the presence of inositol hexakisphosphate fiber-forming solutions of hemoglobin S liberated as much as six protons per tetramer upon oxygen binding. The increased liberation of protons was probably due to a higher affinity of the effectors for the fibers of hemoglobin S. Very likely the higher affinity was supported by a conformational change of hemoglobin S specific for the fibers.

Buffers↗