Cyclopiazonic acid is complexed to a divalent metal ion when bound to the sarcoplasmic reticulum Ca2+-ATPase

We have determined the structure of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) in an E2.P(i)-like form stabilized as a complex with MgF(4)(2-), an ATP analog, adenosine 5'-(beta,gamma-methylene)triphosphate (AMPPCP), and cyclopiazonic acid (CPA). The structure determined at 2.5A resolution leads to a significantly revised model of CPA binding when compared with earlier reports. It shows that a divalent metal ion is required for CPA binding through coordination of the tetramic acid moiety at a characteristic kink of the M1 helix found in all P-type ATPase structures, which is expected to be part of the cytoplasmic cation access pathway. Our model is consistent with the biochemical data on CPA function and provides new measures in structure-based drug design targeting Ca(2+)-ATPases, e.g. from pathogens. We also present an extended structural basis of ATP modulation pinpointing key residues at or near the ATP binding site. A structural comparison to the Na(+),K(+)-ATPase reveals that the Phe(93) side chain occupies the equivalent binding pocket of the CPA site in SERCA, suggesting an important role of this residue in stabilization of the potassium-occluded E2 state of Na(+),K(+)-ATPase.

Antidepressant activity of zinc and magnesium in view of the current hypotheses of antidepressant action

The clinical efficacy of current antidepressant therapies is unsatisfactory; antidepressants induce a variety of unwanted effects, and, moreover, their therapeutic mechanism is not clearly understood. Thus, a search for better and safer agents is continuously in progress. Recently, studies have demonstrated that zinc and magnesium possess antidepressant properties. Zinc and magnesium exhibit antidepressant-like activity in a variety of tests and models in laboratory animals. They are active in forced swim and tail suspension tests in mice and rats, and, furthermore, they enhance the activity of conventional antidepressants (e.g., imipramine and citalopram). Zinc demonstrates activity in the olfactory bulbectomy, chronic mild and chronic unpredictable stress models in rats, while magnesium is active in stress-induced depression-like behavior in mice. Clinical studies demonstrate that the efficacy of pharmacotherapy is enhanced by supplementation with zinc and magnesium. The antidepressant mechanisms of zinc and magnesium are discussed in the context of glutamate, brain-derived neurotrophic factor (BDNF) and glycogen synthase kinase-3 (GSK-3) hypotheses. All the available data indicate the importance of zinc and magnesium homeostasis in the psychopathology and therapy of affective disorders.

Ca-Mg kutnahorite and struvite production by Idiomarina strains at modern seawater salinities

The production of Mg-rich carbonates by Idiomarina bacteria at modern seawater salinities has been investigated. With this objective, four strains: Idiomarina abyssalis (strain ATCC BAA-312), Idiomarina baltica (strain DSM 15154), Idiomarina loihiensis (strains DSM 15497 and MAH1) were used. The strain I. loihiensis MAH1 is a new isolate, identified in the scope of this work. The four moderately halophilic strains precipitated struvite (NH4MgPO4 x 6H2O) crystals that appear encased by small Ca-Mg kutnahorite [CaMg(CO3)2] spheres and dumbbells, which are also regularly distributed in the bacterial colonies. The proportion of Ca-Mg kutnahorite produced by the bacteria assayed ranged from 50% to 20%, and I. abyssalis also produced monohydrocalcite. All precipitated minerals appeared to be related to the bacterial metabolism and, consequently, can be considered biologically induced. Amino acid metabolism resulted in a release of ammonia and CO2 that increase the pH and CO(3)(2-) concentration of the culture medium, creating an alkaline environment that favoured carbonate and struvite precipitation. This precipitation may be also related to heterogeneous nucleation on negatively charged points of biological structures. Because the nature of the organic matrix determines which ion is preferentially adsorbed and, consequently, which mineral phase is formed, the uniquely high content in odd-iso-branched fatty acids of the Idiomarina suggests that their particular membrane characteristics could induce Ca-Mg kutnahorite production. The Ca-Mg kutnahorite, a mineral with a dolomite-ordered structure, production at seawater salinities is noticeable. To date, such precipitation in laboratory cultures, has only been described in hypersaline conditions. It has also been the first time that biomineralization processes have been related to Idiomarina bacteria.

"Ni-struvite" - a new biomineral formed by a nickel resistant Streptomyces acidiscabies

Biomineralization dependent on bacterial activity has been described for struvite which is formed in soils, guano, putrescent matter and sediments. A new biomineral containing nickel instead of magnesium, Ni(NH4)(PO4) . 6H2O, has been identified. It was formed by nickel resistant Streptomyces acidiscabies E13, and putatively named nickel struvite. The mineral formation is dependent on biological activity since non-viable bacterial cells are not capable to induce formation of Ni-struvite under identical conditions. Formation of Ni-struvite was observed on colony surfaces upon prolonged incubation of solid minimal or complex media containing elevated concentrations of 8-15mM NiCl2. The formation of magnesium containing crystals was not observed although Mg2+ is present in the medium. However, the process was not depending on desiccation since small crystals attached to the mycelial biomass of the bacteria were observed microscopically also in liquid cultures of nickel supplemented minimal and complex media after two weeks of incubation. The capacity to induce biomineralization of a nickel containing mineral is postulated to constitute a resistance factor, allowing the soil bacterium to withstand high nickel concentrations. The strain shows nickel resistance as an adaption to its habitat, since this bacterium was isolated from a former uranium mining site in Eastern Thuringia, Germany, where nickel concentrations of up to 2000ppm (translating to appr. 30mM) occur as a result of former mining activities.

Uptake of Cd, Zn and Mn by willow increases during terrestrialisation of initially ponded polluted sediments

Metal concentration of plants growing on contaminated soils among other factors may depend on changes in the hydrological regime of the soil. Foliar and stem metal concentrations in Salix cinerea (grey sallow) were measured in 2 consecutive growing seasons on a submerged sediment-derived soil that underwent gradual terrestrialisation. Foliar and stem cutting concentrations for Cd, Zn and Mn increased on plots that were submerged during the first year, but emerged in the second year of monitoring. The litter layer was sampled under the shrubs of a plot with a recent abrupt change in hydrological regime and on the reference plot. It was separated in three size fractions through sieving. Analysis of the litter fractions suggested that Cd and Zn concentrations remained constant during fragmentation. However, Cr, Cu, Ni and Pb concentrations increased, which was attributed to adhesion of mineral soil particles on the fine fraction. After correction for the metal content in the mineral fraction, an increase in Cd, Mn and Cu concentration during fragmentation of the organic part of the litter layer was observed for the polluted plot. Net litter layer decomposition rate was low, which may indicate low colonisation by the decomposing community. Terrestrialisation resulted in higher Cd, Mn and Zn uptake by willows. The deviant litter layer metal concentrations for Cd, Zn and Mn and low decomposition rate must be further monitored. Feasibility of measures aiming at re-establishing wetland conditions for the dredged sediment landfill must be considered.

ATP as effector of inorganic pyrophosphatase of Escherichia coli. Identification of the binding site for ATP

The interaction of Escherichia coli inorganic pyrophosphatase (E-PPase) with effector ATP has been studied. The E-PPase has been chemically modified with the dialdehyde derivative of ATP. It has been established that in the experiment only one molecule of effector ATP is bound to each subunit of the hexameric enzyme. Tryptic digestion of the adenylated protein followed by isolation of a modified peptide by HPLC and its mass-spectrometric identification has showed that it is an amino group of Lys146 that undergoes modification. Molecular docking of ATP to E-PPase indicates that the binding site for effector ATP is located in a cluster of positively charged amino acid residues proposed earlier on the basis of site-directed mutagenesis to participate in binding of effector pyrophosphate. Molecular docking also reveals several other amino acid residues probably involved in the interaction with effectors.

Biomineralization of carbonate and phosphate by moderately halophilic bacteria

We investigated the precipitation of carbonate and phosphate minerals by 19 species of moderately halophilic bacteria using media with variable Mg(2+)/Ca(2+) ratios. The precipitated minerals were calcite, magnesium (Mg) calcite, and struvite (MgNH(4)PO(4) x 6H(2)O) in variable proportions depending on the Mg(2+)/Ca(2+) ratio of the medium. The Mg content of the Mg-calcite decreased with increasing Ca(2+) concentration in the medium. According to the saturation indices, other minerals could also have precipitated. We observed important differences between the morphology of carbonate and phosphate, which may help us to recognize these minerals in natural systems. We studied the growth and pH curves of four bacteria in media specific for carbonate and struvite precipitation. We consider the biomineralization processes that produce carbonate and phosphate minerals, and propose a hypothesis for the lack of struvite in natural environments and ancient rocks.

Use of a seeder reactor to manage crystal growth in the fluidized bed reactor for phosphorus recovery

The authors have been engaged in the development of a phosphorus recovery system capable of maintaining high recovery efficiencies, with the chemical cost suppressed. This time, they conducted demonstration tests of a fluidized bed magnesium ammonium phosphate reactor provided with a seeder reactor for the supernatant from anaerobic digestion using a pilot experimental plant with a wastewater treatment capacity of 20 m3/d. For the digestion supernatant with a phosphorus concentration of approximately 300 mg/L, the treated water phosphorus concentration was 10 to 25 mg/L, and the phosphorus recovery efficiency was more than 90%. Relative to the chemical cost in the case of magnesium chloride, the chemical cost in the case of magnesium hydroxide is approximately 40%. Thus, with the new system, it was possible to reduce the running cost while maintaining high recovery efficiencies.

Struvite precipitation thermodynamics in source-separated urine

Struvite (MgNH(4)PO(4).6H(2)O) precipitation eliminates phosphate efficiently from urine, a small but highly concentrated stream in the total flux of domestic wastewater. Precipitation experiments with hydrolysed urine evaluated the solubility product of struvite. The stored and fully hydrolysed urine had an ionic strength of between 0.33 and 0.56M and required the estimation of activity coefficients. From our data, we identified the Davies approximation with the two constants A=0.509 and B=0.3 as agreeing best with our laboratory results. The standard solubility product K(s)(0)=f(1)[NH4(+)]f(2)[Mg2+]f(3)[PO(4)(3-)] ([ ]=concentration of the species; f(x)=corresponding activity coefficient) of struvite in urine was found to be 10(-13.26+/-0.057) at 25 degrees C and the enthalpy of struvite formation DeltaH was 22.6(+/-1.1) kJmol(-1). The equilibrium calculations required the following dissolved complexes: [MgCO(3)](aq), [MgHCO(3)](+), [MgPO(4)](-), [NH4HPO4and [NaHPO(4)](-) and to a lesser extent [MgSO(4)](aq) and [NH(4)SO(4)](-). Organic complexes do not seem to influence the solubility product substantially. For practical purposes, a conditional solubility product K(s)(cond)=[Mg(aq)].[NH(4)(+)+NH(3)].[P(ortho)]=10(-7.57)M(3) was derived to calculate struvite solubility in urine at 25 degrees C, pH=9.0 and ionic strength I=0.4M directly from measured concentrations.

Synthesis, characterization and DNA binding of magnesium–ciprofloxacin (cfH) complex [Mg(cf)2]·2.5H2O

Interactions of the tested systems (title compound [Mg(cf)(2)] * 2.5H(2)O (1), ciprofloxacin (cfH) and ciprofloxacin in the mixture with MgCl(2)), with single and double stranded calf thymus DNA, poly[d(AT)] * poly[d(AT)] and poly[d(GC)] * poly[d(GC)] were studied by UV-spectrophotometric (melting curves) and fluorescence emission measurements. Pronounced quenching of ciprofloxacin's fluorescence intensity has been observed for all the tested compounds after titration with various GC containing DNA molecules. It seems probable that quenching originates in the electron transfer from guanine to the photo-excited fluoroquinolone. The UV-spectrophotometric results obtained for 1 are substantially different from the other solutions and the biggest differences were observed for GC containing DNAs. Solution of 1 provokes a large thermal destabilization of poly[d(GC)] * poly[d(GC)]. This process is irreversible which suggests that the species present in solution of 1 alone inhibit re-annealing by associating irreversibly with the single strands. We have realized that aqueous solutions of 1 are colloidal and we propose that colloidal particles are involved in specific binding to GC containing sequences, most probably in the major groove of DNA.

Magnesium requirements: new estimations for men and women by cross-sectional statistical analyses of metabolic magnesium balance data

BACKGROUND

Current recommendations for magnesium requirements are based on sparse balance data.

OBJECTIVE

To provide new estimates of the average magnesium requirement for men and women, we pooled magnesium data from 27 different tightly controlled balance studies conducted at the US Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND.

DESIGN

Magnesium balance data (magnesium intake - [fecal magnesium + urinary magnesium]) (664 data points) were collected from 243 subjects (women: n = 150; weight: 71.6 +/- 16.5 kg; age: 51.3 +/- 17.4 y; men: n = 93, weight: 76.3 +/- 12.5 kg; age: 28.1 +/- 8.1 y). Data from the last 6-14 d of each dietary period (> or =28 d) of each study were analyzed and were excluded if individual intakes of calcium, copper, iron, phosphorus, or zinc fell below respective estimated average requirements (EARs) or exceeded 99th percentiles of usual intakes of those elements (iron: above the upper limit) from the 1994 Continuing Survey of Food Intakes by Individuals. Daily intakes of magnesium ranged between 84 and 598 mg. The relation between magnesium intake and magnesium output was investigated by fitting random coefficient models.

RESULTS

The models predicted neutral magnesium balance [defined as magnesium output (Y) equal to magnesium intake (M)] at magnesium intakes of 165 mg/d [95% prediction interval (PI): 113, 237 mg/d; Y = 19.8 + 0.880 M], 2.36 mg . kg(-1) . d(-1) (95% PI: 1.58, 3.38 mg . kg(-1) . d(-1); Y = 0.306 + 0.870 M), or 0.075 mg . kcal(-1) . d(-1) (95% PI: 0.05, 0.11 mg . kcal(-1) . d(-1); Y = 0.011 + 0.857 M). Neither age nor sex affected the relation between magnesium intake and output.

CONCLUSION

The findings suggest a lower magnesium requirement for healthy men and women than estimated previously.

A Trojan horse transition state analogue generated by MgF3- formation in an enzyme active site

Identifying how enzymes stabilize high-energy species along the reaction pathway is central to explaining their enormous rate acceleration. beta-Phosphoglucomutase catalyses the isomerization of beta-glucose-1-phosphate to beta-glucose-6-phosphate and appeared to be unique in its ability to stabilize a high-energy pentacoordinate phosphorane intermediate sufficiently to be directly observable in the enzyme active site. Using (19)F-NMR and kinetic analysis, we report that the complex that forms is not the postulated high-energy reaction intermediate, but a deceptively similar transition state analogue in which MgF(3)(-) mimics the transferring PO(3)(-) moiety. Here we present a detailed characterization of the metal ion-fluoride complex bound to the enzyme active site in solution, which reveals the molecular mechanism for fluoride inhibition of beta-phosphoglucomutase. This NMR methodology has a general application in identifying specific interactions between fluoride complexes and proteins and resolving structural assignments that are indistinguishable by x-ray crystallography.

Rat strains differ in susceptibility to Ureaplasma parvum-induced urinary tract infection and struvite stone formation

Individuals with struvite uroliths are susceptible to recurrent urinary tract infections (UTI), sepsis, and renal disease. Unfortunately, little is known about the host-specific factors that predispose to this disease. In order to develop a rodent model that can address this problem, we inoculated female Fischer 344 (F344), Lewis (LEW), Sprague-Dawley (SD), and Wistar (WIS) rats with a host-adapted strain of Ureaplasma parvum. Animals were necropsied at 2 weeks postinoculation; 100% of F344, 42% of SD, 10% of LEW, and 10% of WIS rats remained infected. Severe bladder lesions and struvite calculi were seen in 64% of F344 rats; in other rat strains, bladder lesions were mild or absent. F344 rats with struvite uroliths had the highest urinary levels of proinflammatory cytokines, such as GRO/KC, interleukin-1alpha (IL-1alpha), and IL-1beta. F344 rats without struvite stones at necropsy had milder bladder lesions and significantly lower urinary levels of proinflammatory cytokines but a more prominent inflammatory response than did other rat strains. Based on our results, struvite stone formation is linked to a robust inflammatory response that does not resolve UTI but instead promotes damage to surrounding tissues.

Modulation of crystalline Proteus mirabilis biofilm development on urinary catheters

The crystalline biofilms formed by Proteus mirabilis can seriously complicate the care of patients undergoing long-term bladder catheterization. The generation of alkaline urine by the bacterial urease causes calcium and magnesium phosphates to precipitate from urine and accumulate in the catheter biofilm, blocking the flow of urine from the bladder. The pH at which these salts crystallize from a urine sample, the nucleation pH (pH(n)), can be elevated by diluting the urine and by increasing its citrate content. The aim of this study was to examine whether manipulation of pH(n) in these ways modulated the rate at which crystalline biofilm developed. Experiments in laboratory models of the catheterized bladder infected with P. mirabilis showed that when the bladder was supplied with a concentrated urine (pH(n) 6.7) at a low fluid output (720 ml per 24 h), catheters blocked at 19-31 h. Diluting this urine 1:4 increased the pH(n) to 7.5 and models supplied with this urine at 2880 ml per 24 h took 110-137 h to block. When models were supplied with urine containing citrate at 1.5 mg ml(-1) or above (pH(n) 8.3-9.1), the catheters drained freely for the full 7 day experimental period. Scanning electron microscopy revealed that the catheter biofilms that developed in urine with high pH(n) values were devoid of crystalline formations. These observations should encourage a clinical trial to examine the effect of increasing a patient's fluid intake with citrate-containing drinks on the encrustation and blockage of catheters.

[The role of macro-elements in the human body]

The authors summarize the role of essential macro metal elements (Na, K, Ca, Mg) in human body: their homeostasis, absorption, transport, storage and excretion. Metabolism of macro-elements, daily requirements, cause of metal deficiencies and diseases caused by deficiencies are also discussed. Messenger and prooxidant effect of Ca2+-ions, indirect antioxidant effect of Mg2+-ions and the adjuvant application of magnesium are also reviewed.

Channel phosphorylation and modulation of L-type Ca2+ currents by cytosolic Mg2+ concentration

Previous studies have shown that inhibition of L-type Ca(2+) current (I(Ca)) by cytosolic free Mg(2+) concentration ([Mg(2+)](i)) is profoundly affected by activation of cAMP-dependent protein kinase pathways. To investigate the mechanism underlying this counterregulation of I(Ca), rat cardiac myocytes and tsA201 cells expressing L-type Ca(2+) channels were whole cell voltage-clamped with patch pipettes in which [Mg(2+)] ([Mg(2+)](p)) was buffered by citrate and ATP. In tsA201 cells expressing wild-type Ca(2+) channels (alpha(1C)/beta(2A)/alpha(2)delta), increasing [Mg(2+)](p) from 0.2 mM to 1.8 mM decreased peak I(Ca) by 76 +/- 4.5% (n = 7). Mg(2+)-dependent modulation of I(Ca) was also observed in cells loaded with ATP-gamma-S. With 0.2 mM [Mg(2+)](p), manipulating phosphorylation conditions by pipette application of protein kinase A (PKA) or phosphatase 2A (PP(2A)) produced large changes in I(Ca) amplitude; however, with 1.8 mM [Mg(2+)](p), these same manipulations had no significant effect on I(Ca). With mutant channels lacking principal PKA phosphorylation sites (alpha(1C/S1928A)/beta(2A/S478A/S479A)/alpha(2)delta), increasing [Mg(2+)](p) had only small effects on I(Ca). However, when channel open probability was increased by alpha(1C)-subunit truncation (alpha(1CDelta1905)/beta(2A/S478A/S479A)/alpha(2)delta), increasing [Mg(2+)](p) greatly reduced peak I(Ca). Correspondingly, in myocytes voltage-clamped with pipette PP(2A) to minimize channel phosphorylation, increasing [Mg(2+)](p) produced a much larger reduction in I(Ca) when channel opening was promoted with BAY K8644. These data suggest that, around its physiological concentration range, cytosolic Mg(2+) modulates the extent to which channel phosphorylation regulates I(Ca). This modulation does not necessarily involve changes in channel phosphorylation per se, but more generally appears to depend on the kinetics of gating induced by channel phosphorylation.

Inhibition of the ATPase activity of Escherichia coli ATP synthase by magnesium fluoride

Inhibition of ATPase activity of Escherichia coli ATP synthase by magnesium fluoride (MgFx) was studied. Wild-type F(1)-ATPase was inhibited potently, albeit slowly, when incubated with MgCl(2), NaF, and NaADP. The combination of all three components was required. Reactivation of ATPase activity, after removal of unbound ligands, occurred with half-time of approximately 14 h at 22 degrees C and was quasi-irreversible at 4 degrees C. Mutant F(1)-ATPases, in which catalytic site residues involved in transition state formation were modified, were found to be resistant to inhibition by MgFx. The data demonstrate that MgFx in combination with MgADP behaves as a tight-binding transition state analog in E. coli ATP synthase.

Kidney stone disease

About 5% of American women and 12% of men will develop a kidney stone at some time in their life, and prevalence has been rising in both sexes. Approximately 80% of stones are composed of calcium oxalate (CaOx) and calcium phosphate (CaP); 10% of struvite (magnesium ammonium phosphate produced during infection with bacteria that possess the enzyme urease), 9% of uric acid (UA); and the remaining 1% are composed of cystine or ammonium acid urate or are diagnosed as drug-related stones. Stones ultimately arise because of an unwanted phase change of these substances from liquid to solid state. Here we focus on the mechanisms of pathogenesis involved in CaOx, CaP, UA, and cystine stone formation, including recent developments in our understanding of related changes in human kidney tissue and of underlying genetic causes, in addition to current therapeutics.

Auto-nucleation and crystal growth of struvite in a demonstrative fluidized bed reactor (FBR)

The experience of P removal by auto-nucleation and crystal growth of struvite (MAP) in a demonstrative plant is proposed. The demonstrative plant is located in a municipal wastewater treatment plant in northern Italy. The trials are a consequence of previous experimentation carried out using silica sand as seed material. Working in metastable conditions the auto-nucleation process is performed, and allows the control of the precipitation and the growth of MAP inside the FBR reactor. No scaling problems are observed in the collecting pipes. After the treatment of 650m3 of anaerobic supernatants, 0.28 tons of granulated crystalline MAP are produced. The chemical analysis shows its possible use in agriculture as fertilizer. Operative costs analysis confirms the SCP as a cheap way to remove and recover P from anaerobic supernatants.

Kinetic studies of yeast polyA polymerase indicate an induced fit mechanism for nucleotide specificity

Polyadenylate polymerase (PAP) catalyzes the synthesis of 3'-polyadenylate tails onto mRNA. A comprehensive steady-state kinetic analysis of PAP was conducted which included initial velocity studies of the forward and reverse reactions, inhibition studies, and the use of alternative substrates. The reaction (A(n) + ATP <--> A(n+1) + PP(i)) is adequately described by a rapid equilibrium random mechanism. Several thermodynamic parameters for the reaction were determined or calculated, including the overall equilibrium constant (K(eq) = 84) and the apparent equilibrium constant of the internal step (K(int) = 4) which involves the rate-determining interconversion of central complexes. A large (100-fold) difference in Vmax accounts for nucleotide specificity (ATP vs CTP), despite an only 3-fold difference in Km. Comparison of the sulfur elemental effect on Vmax for ATP and CTP suggests that the chemical step is rate-determining for both reactions. Comparison of the sulfur elemental effect on Vmax/Km revealed differences in the mechanism by which either nucleotide is incorporated. Consistent with these data, an induced fit mechanism for nucleotide specificity is proposed whereby PAP couples a uniform binding mechanism, which selects for ATP, with a ground-state destabilization mechanism, which serves to accelerate the velocity for the correct substrate.

Cellular and molecular gateways to urolithiasis: a new insight

Urolithiasis is a relevant clinical problem in everyday practice with a subsequent burden for the health system. Urolithiasis is classically explained as the derangement in the process of biomineralization involving the equilibrium between promoters and inhibitors of crystallization: a deficit of one or several inhibitors or an excess of one or several promoters plays a pivotal role in the stone formation. The revolutionary introduction of the molecular biology in medicine has given a new insight in urolithiasis too. Genetic factors have also been postulated to play an important role. A review of the current knowledge on urolithiasis based upon a molecular and genetic approach is reported.

Formation of insoluble magnesium phosphates during growth of the archaea Halorubrum distributum and Halobacterium salinarium and the bacterium Brevibacterium antiquum

Stationary phase cells of the halophilic archaea Halobacterium salinarium and Halorubrum distributum, growing at 3-4 M NaCl, and of the halotolerant bacterium Brevibacterium antiquum, growing with and without 2.6 NaCl, took up approximately 90% of the phosphate from the culture media containing 2.3 and 11.5 mM phosphate. The uptake was blocked by the uncoupler FCCP. In B. antiquum, EDTA inhibited the phosphate uptake. The content of polyphosphates in the cells was significantly lower than the content of orthophosphate. At a high phosphate concentration, up to 80% of the phosphate taken up from the culture medium was accumulated as Mg(2)PO(4)OH x 4H(2)O in H. salinarium and H. distributum and as NH(4)MgPO(4) x 6H(2)O in B. antiquum. Consolidation of the cytoplasm and enlargement of the nucleoid zone were observed in the cells during phosphate accumulation. At phosphate surplus, part of the H. salinarium and H. distributum cell population was lysed. The cells of B. antiquum were not lysed and phosphate crystals were observed in the cytoplasm.

Optimum doses of Mg and P salts for precipitating ammonia into struvite crystals in aerobic composting

It was previously reported that struvite crystals could be formed in the aerobic composting reaction provided that Mg and P salts are added [Bioresource Technology 79 (2001) 129]. The formation of struvite crystals significantly reduced gaseous loss of ammonia and resulted in substantial increase in the ammonia content in the compost, attaining 1.5%. In this context, the present study was conducted to determine the optimal doses of Mg and P salts for struvite crystallization. It was found that cumulative ammonia production was about 33-36% of the initial total nitrogen in the aerobic composting reaction, irrespective of the amounts of Mg and P salts added. The theoretical doses for complete conversion of ammonia into struvite crystals seemed to be about 33-36% of the initial nitrogen. The addition of Mg and P salts at this level, however, caused adverse effects on the degradation of organic materials. Therefore, it was concluded that the optimal doses of Mg and P salts should be about 20% of the initial nitrogen in the compost mixture not to cause any harmful effects on the composting reaction.

Metal-free PPi activates hydrolysis of MgPPi by an Escherichia coli inorganic pyrophosphatase

Soluble inorganic pyrophosphatase from Escherichia coli (E-PPase) is a hexamer forming under acidic conditions the active trimers. We have earlier found that the hydrolysis of a substrate (MgPP(i)) by the trimers as well as a mutant E-PPase Asp26Ala did not obey the Michaelis-Menten equation. To explain this fact, a model has been proposed implying the existence of, aside from an active site, an effector site that can bind PP(i) and thus accelerate MgPP(i) hydrolysis. In this paper, we demonstrate that the noncompetitive activation of MgPP(i) hydrolysis by metal-free PP(i) can also explain kinetic features of hexameric forms of both the native enzyme and the specially obtained mutant E-PPase with a substituted residue Glu145 in a flexible loop 144-149. Aside from PP(i), its non-hydrolyzable analog methylene diphosphonate can also occupy the effector site resulting in the acceleration of the substrate hydrolysis. Our finding that two moles of [32P]PP(i) can bind with each enzyme subunit is direct evidence for the existence of the effector site in the native E-PPase.