Absence Of Potassium Ions Research Articles

Study of Co-crystallization of Neodymium and Strontium Sulfates in the Absence of Potassium Ions

Study of Co-crystallization of Neodymium and Strontium Sulfates in the Absence of Potassium Ions

CRTAC1 has a Compact β-propeller–TTR Core Stabilized by Potassium Ions

Cartilage acidic protein-1 (CRTAC1) is a secreted glycoprotein with roles in development, function and repair of the nervous system. It is linked to ischemic stroke, osteoarthritis and (long) COVID outcomes, and has suppressive activity in carcinoma and bladder cancer. Structural characterization of CRTAC1 has been complicated by its tendency to form disulfide-linked aggregates. Here, we show that CRTAC1 is stabilized by potassium ions. Using x-ray crystallography, we determined the structure of CRTAC1 to 1.6 Å. This reveals that the protein consists of a three-domain fold, including a previously-unreported compact β-propeller–TTR combination, in which an extended loop of the TTR plugs the β-propeller core. Electron density is observed for ten bound ions: six calcium, three potassium and one sodium. Low potassium ion concentrations lead to changes in tryptophan environment and exposure of two buried free cysteines located on a β-blade and in the β-propeller-plugging TTR loop. Mutating the two free cysteines to serines prevents covalent intermolecular interactions, but not aggregation, in absence of potassium ions. The potassium ion binding sites are located between the blades of the β-propeller, explaining their importance for the stability of the CRTAC1 fold. Despite varying in sequence, the three potassium ion binding sites are structurally similar and conserved features of the CRTAC protein family. These insights into the stability and structure of CRTAC1 provide a basis for further work into the function of CRTAC1 in health and disease.

Elucidation of Novel Potassium-Mediated Oxidation and Etching of Two-Dimensional Transition Metal Dichalcogenides.

Preparation of edge-rich two-dimensional (2D) transition metal dichalocogenides (TMDs) has been actively investigated with the aim to improve their electrical and catalytic properties. Here, we elucidate the role of potassium ions in oxidation of TMDs and suggest a consequent novel anisotropic etching mechanism driven by self-running oxide droplets. We discover that potassium-mediated oxidation of MoS2 leads to the formation of K-intercalated hexagonal-phase molybdenum oxides (h-KxMoO3), whereas orthorhombic-phase oxides are formed in the absence of potassium ions. Metastable h-KxMoO3 appears to have decomposed into oxide droplets at higher temperature. Self-running of the oxide droplets leads to layer-by-layer anisotropic etching of MoS2 along the armchair direction. The motion of the droplets appears to be triggered by the surface energy instability between the oxide droplets and the underlying MoS2 layer. This study opens new possibilities to design and manufacture novel edge-rich 2D TMDs that do not follow the equilibrium Wulff shape by modulating their oxidation with the assistance of alkali metals and also offers fundamental insights into the interactions between nanodroplets and 2D materials toward edge engineering.

Metallo-responsive self-assembly of lipophilic guanines in hydrocarbon solvents: a systematic SAXS structural characterization.

Lipophilic guanines (LipoGs) in aprotic solvents undergo different self-assembly processes based on different H-bonded motifs. Cylindrical nanotubes made by π-π stacked guanine tetramers (G-quadruplexes) and flat, tape-like aggregates (G-ribbons) have been observed depending on the presence of alkali metal ions. To obtain information on the structural properties and stability of these LipoG aggregates, Small-Angle X-ray Scattering (SAXS) experiments have been performed in dodecane, both in the presence and in the absence of potassium ions. As a result, the occurrence of the two different metallo-responsive architectures (nanoribbons or columnar nanotubes) was confirmed and we reported here for the first time a systematic study on the dependence of the aggregate properties on composition, temperature and molecular unit structure. Even if dodecane was selected to favour LipoG solubility, a strong tendency to self-organize into ordered lyotropic phases was indeed detected.

Методика розрахунку прямотечійнo-протитечійного розчинення калійної руди

Наведено результати теоретичного та експериментального дослідження процесу розчинення калійної руди, основу якої складають сполуки калій хлориду та калій сульфату. Подано результати експериментального дослідження розчинення калійної солі у реакторі з механічним та пневматичним перемішуванням, який імітував одну з комірок промислового апарата. Фізично змодельовано цей процес у реакторі з механічним перемішуванням. Процес розчинення проведено за низьких чисел обертів, які становили 80 об/хв, що імітувало розчинення у промисловому шнековому апараті-розчиннику, у якому тверда фаза переміщається шнеком по дну апарата, а рідина рухається над поверхнею твердої фази, при цьому тверда фаза не переходить у зважений стан. Транспортування твердої солі шнеком перемішує її та оновлює поверхню контакту солі з рідиною. Визначення коефіцієнта масовіддачі проведено під час розчинення калійної руди у насиченому розчині натрій хлориду за відсутності у ньому іонів калію, так і за їх наявності, що відповідає промисловим умовам розчинення і є необхідною умовою розчинення для кристалізації калійної солі. Наведено основні параметри процесу розчинення калійної солі у насиченому розчині натрій хлориду. На основі рівняння масовіддачі визначено коефіцієнт масовіддачі під час механічного перемішування та пневматичного барботування розчину. Досліджено розчинення калійної солі за умов механічного перемішування та додаткової подачі нагрітого повітря. Наведено методики розрахунку системи апаратів-розчинників у протитечійно-прямотечійній схемі розчинення. Для промислового розчинника на основі рівнянь матеріального балансу та кінетики складено математичну модель, яка описує процес розчинення. Розглянуто систему трьох апаратів-розчинників, кожен з яких розділений вертикальною перегородкою на дві комірки, що імітують реактор ідеального перемішування. У кожному апараті фази рухаються прямотечійно. У системі трьох апаратів рух твердої та рідкої фаз відбувається протитечійно. Рішення математичної моделі представлено у графічному вигляді.

A study of the effects of flocalin on respiration and potassium transport of rat-heart and liver mitochondria

The effects of the drug flocalin, which possesses cardioprotective properties, on the respiration rates of rat-heart and liver mitochondria in different functional states, the efficiency of oxidative phosphorylation, as well as the transport of potassium ions in these organelles, were studied. It was found that flocalin at concentrations of 7–30 μm stimulated respiration of rat-heart and liver mitochondria in V2 and V4 states in the presence of succinic add as a respiration substrate in a potassium-containing medium. In the absence of potassium ions in the incubation medium, flocalin had no effect on mitochondrial respiration in these states. Studying the functioning of the potassium transport system revealed that flocalin at these concentrations dose-dependently activated the ATP-dependent transport of potassium ions in rat-heart and liver mitochondria. The data we obtained indicate that the cardioprotective effect of flocalin can be associated with activation of the ATP-dependent potassium channel of the inner mitochondrial membrane.

Dioldehydrase: An Essential Role for Potassium Ion in the Homolytic Cleavage of the Cobalt−Carbon Bond in Adenosylcobalamin

The complex of dioldehydrase with adenosylcobalamin (coenzyme B12) and potassium ion reacts with molecular oxygen in the absence of a substrate to oxidize coenzyme and inactivate the complex. In this article, high performance liquid chromatography and mass spectral analysis are used to identify the nucleoside products resulting from oxygen inactivation. The product profile indicates that oxygen inactivation proceeds by direct reaction of molecular oxygen with the 5'-deoxyadenosyl radical and cob(II)alamin. Formation of 5'-peroxyadenosine as the initial nucleoside product chemically correlates this reaction with aerobic, aqueous photoinduced homolytic cleavage of adenosylcobalamin (Schwartz, P. A., and Frey, P. A., (2007) Biochemistry, in press), indicating that both reactions proceed through similar chemical intermediates. The oxygen inactivation of the enzyme-coenzyme complex shows an absolute requirement for the same monocations required in catalysis by dioldehydrase. Measurements of the dissociation constants for adenosylcobalamin from potassium-free (Kd = 16 +/- 2 microM) or potassium-bound dioldehydrase (Kd = 0.8 +/- 0.2 microM) reveal that the effect of the monocation in stimulating oxygen sensitivity cannot be explained by an effect on the binding of coenzyme to the enzyme. Cross-linking experiments suggest that the full quaternary structure is assembled in the absence of potassium ion under the experimental conditions. The results indicate that dioldehydrase likely harvests the binding energy of the activating monocation to stimulate the homolytic cleavage of the Co-C5' bond in adenosylcobalamin.

Purification, crystallization and structure determination of native GroEL from Escherichia coli lacking bound potassium ions.

GroEL is a member of the ATP-dependent chaperonin family that promotes the proper folding of many cytosolic bacterial proteins. The structures of GroEL in a variety of different states have been determined using X-ray crystallography and cryo-electron microscopy. In this study, a 3.02 A crystal structure of the native GroEL complex from Escherichia coli is presented. The complex was purified and crystallized in the absence of potassium ions, which allowed evaluation of the structural changes that may occur in response to cognate potassium-ion binding by comparison to the previously determined wild-type GroEL structure (PDB code 1xck), in which potassium ions were observed in all 14 subunits. In general, the structure is similar to the previously determined wild-type GroEL crystal structure with some differences in regard to temperature-factor distribution.

Treatment of radioactive liquid waste by sorption on natural zeolite in Turkey

Liquid radioactive waste has been generated from the use of radioactive materials in industrial applications, research and medicine in Turkey. Natural zeolites (clinoptilolite) have been studied for the removal of several key radionuclides (137Cs, 60Co, 90Sr and 110mAg) from liquid radioactive waste. The aim of the present study is to investigate effectiveness of zeolite treatment on decontamination factor (DF) in a combined process (chemical precipitation and adsorption) at the laboratory tests and scale up to the waste treatment plant. In this study, sorption and precipitation techniques were adapted to decontamination of liquid low level waste (LLW). Effective decontamination was achieved when sorbents are used during the chemical precipitation. Natural zeolite samples were taken from different zeolite formations in Turkey. Comparison of the ion-exchange properties of zeolite minerals from different formations shows that Gordes clinoptilolite was the most suitable natural sorbent for radionuclides under dynamic treatment conditions and as an additive for chemical precipitation process. Clinoptilolite were shown to have a high selectivity for 137Cs and 110mAg as sorbent. In the absence of potassium ions, native clinoptilolite removed 60Co and 90Sr very effectively from the liquid waste. In the end of this liquid waste treatment, decontamination factor was provided as 430 by using 0.5mm clinoptilolite at 30°C.

Twitch potentiation induced by caffeine in the mouse diaphragm depends on external calcium ions in the absence of potassium ions

1. 1. Removal of external K + ions increases the amplitude of directly elicited twitch contractions of the mouse diaphragm (Nishimura et al., 1996). This increase depends on external Ca 2+ ions. 2. 2. We examined the effect of caffeine (2 mM) on this increase in twitch amplitude. The mouse diaphragm muscle was directly stimulated in the presence of d-tubocurarine (10 μM). 3. 3. Caffeine increased the amplitude of twitches in a standard bathing solution. This effect was maintained in a solution without either K + or Ca 2+ ions but was abolished in a solution from which both ions were absent. Readdition of Ca 2+ ions restored the potentiating effect of caffeine. 4. 4. In the presence of caffeine, removal of both K + and Ca 2+ ions decreased the resting membrane potentials of muscle fibers to about−53 mV. The readdition of 2 mM Ca 2+ ions restored the membrane potentials. 5. 5. Twitch potentiation in the absence of external K + ions was attenuated by 10 μM bepridil but not by 3 μM verapamil or 10 μM Cd 2+ ions. 6. 6. These results support the hypothesis that Na +-Ca 2+ exchange can support twitch contraction during the inhibition of Na +-K +-ATPase activity. The influx of Ca 2+ ions into the cells might be stored in the sarcoplasmic reticulum.

Immunotitration Analysis of Cytosolic Acetoacetyl-Coenzyme A Thiolase Activity in Human Fibroblasts

There are five known thiolases in human fibroblasts, and all but mitochondrial trifunctional protein (TFP) have thiolase activity toward acetoacetyl-CoA (AACoA). We investigated the contribution of mitochondrial acetoacetyl-CoA thiolase (AACoAT) (T2), cytosolic AACoAT (CT), and mitochondrial 3-ketoacyl-CoA thiolase (T1) to the total AACoAT activity in control human fibroblasts. Immunotitration of AACoAT activity with antibodies against T2, CT, or T1 was carried out in control fibroblasts, with the following results. In the case of AACoAT activity in the absence of potassium ion, 26-38%, 40-47%, and 11-20% of the total activity derived from CT, T1, and T2, respectively. The residual 6-9% total activity was not immunotitrated when three antibodies were used in combination. Hence, the contribution of peroxisomal 3-ketoacyl-CoA thiolase to the total AACoAT activity in the absence of potassium ion was at least less than 6-9%. Because the normal range of total AACoAT activity is relatively wide, it is difficult to evaluate CT defects based on a decrease of total AACoAT activity. Immunotitration with anti-CT antibody in six control fibroblasts revealed that CT activity ranges between 1.3 and 2.4 nmol/min/mg of protein. Immunotitration proved to be an accurate method to evaluate CT activity. The two cell lines from patients with CT deficiency have become extinct.

Mutant Glu781-->Ala of the rat kidney Na+,K(+)-ATPase displays low cation affinity and catalyzes ATP hydrolysis at a high rate in the absence of potassium ions.

Site-specific mutagenesis was used to replace Glu329, Glu781, Asp806, Thr809, and Asp810 in the transmembrane domain of the ouabain-insensitive alpha 1-isoform of rat kidney Na+,K(+)-ATPase. cDNAs encoding any of the mutants Glu329-->Ala, Glu781-->Ala, Asp806-->Asn, Thr809-->Ala, and Asp810-->Asn were transfected into COS cells, and transfectants were grown in the presence of ouabain to inhibit the endogenous COS cell Na+,K(+)-ATPase. Mutants Glu781-->Ala and Thr809-->Ala were functional as evidenced by their ability to confer ouabain resistance to the cells, whereas mutants Glu329-->Ala, Asp806-->Asn, and Asp810-->Asn were inactive. The apparent Na+ affinities determined by titrations of Na+,K(+)-ATPase activity, Na(+)-ATPase activity, and phosphorylation from ATP in mutants Glu781-->Ala and Thr809-->Ala were strongly reduced relative to the affinity of the wild type (6-8-fold increase in K0.5 for Na+ in the phosphorylation assay for both mutants). The Glu781-->Ala mutant displayed a 3-4-fold reduction in the apparent affinity for K+ and was able to hydrolyze ATP at a high rate in the absence of K+ (Vmax for Na(+)-ATPase activity 5-fold higher than that of the wild-type enzyme). The steady-state phosphoenzyme level formed by the Glu781-->Ala mutant was increased 3-fold by addition of oligomycin, whereas only a slight effect of oligomycin was observed for mutant Thr809-->Ala and the wild type.(ABSTRACT TRUNCATED AT 250 WORDS)

31P and 23Na nuclear magnetic resonance studies of resting and stimulated mast cells

Exocytosis induced by crosslinking the type I receptor for Fc e, domains present on rat mucosal mast cells (RBL-2H3-line) requires the influx of Ca 2+ ions and is markedly influenced by the concentration of monovalent cations (K +, Na + and protons) in their medium. We investigated the role of these ions in coupling the immunological stimulus to secretion using NMR spectroscopy to monitor simultanously intraccllular pH, ATP and Na + concentrations and the secretory response of living adherent mast cells. Using this methodology we observed that: (i) ATP concentration and intracellular pH are highly regulated and no changes could be resolved in them upon stimulation and during exocytosis. (ii) In the absence of potassium ions in the cells' medium, a decrease is observed in the intracellular pH and ATP concentration and an increase in the Na + concentration. (iii) From the influx of extracellular Na + following inhibition of the Na +, K +-ATPase by ouabain, we estimated the inward Na + current of resting cells to 5 × 10 7 ions/(cell·s). This value does not vary by more than 10% during exocytosis.

Valinomycin binds stoichiometrically to cytochrome c oxidase and changes its structure and function

Valinomycin binds to soluble and reconstituted cytochrome c oxidase (COX) in a stoichiometric manner, as shown by a spectral shift of the oxidized gamma-band. No spectral change is found with nigericin or 18-crown-6 and in the absence of potassium ions. Titration of the proton pumping activity of reconstituted COX with valinomycin reached a maximum of H+/e- - 0.73 after addition of 1 mole of valinomycin per mole of reconstituted COX. It is concluded that K+-translocation in proton-pumping COX vesicles occurs via enzyme-bound valinomycin.

Characterization of ouabain-sensitive phosphatase activity in the absence of potassium ion in purified pig kidney Na,K-ATPase.

The ouabain-sensitive phosphatase activity of purified pig kidney Na,K-ATPase preparation in the absence of potassium ion ((-K)phosphatase) was examined precisely. During the preparation procedures, the (-K)3-O-methylfluoresceinphosphatase ((-K)3-OMFPase) activity or the (-K)p-nitrophenylphosphatase ((-K)pNPPase) activity appeared to be purified in parallel with the Na,K-ATPase activity. The (-K)phosphatase activity was competitively inhibited by ATP and by ADP, with the K1 values of 0.25 microM and 1.4 microM, respectively. These values are consistent with their Kd values for the high-affinity ATP binding site of the Na,K-ATPase (Hegyvary, C. & Post, R.L. (1971) J. Biol. Chem. 246, 5234-5240). The substrate, pNPP, apparently competed with covalently bound fluorescein-5'-isothiocyanate (FITC), which is known to bind in the neighborhood of the high-affinity ATP binding site of the Na,K-ATPase, in both the (-K)phosphatase and the (+K)phosphatase reactions. The FITC-fluorescence intensity of FITC-labeled enzyme at the maximal steady-state activity of the (-K)phosphatase reaction was at a similar level to that of the E2 species. However, the FITC-labeled enzyme in the presence of only magnesium ion or only pNPP gave a fluorescence level similar to that of the E1 species. Oligomycin inhibited the (-K)phosphatase activity by at most 46%. On the basis of these results, it is strongly suggested that the (-K)phosphatase reaction is catalyzed at the high-affinity ATP binding site of Na,K-ATPase, and the (-K)phosphatase reaction proceeds in a cyclic manner (E1----E2----E1).

Induction of amphibian oocyte maturation by polyvalent cations and alkaline pH in the absence of potassium ions

The maturation of Xenopus laevis oocytes was studied in media free of added potassium salts. Under these conditions maturation could be triggered by 1 m M Mn 2+ and La 3+ and, to a lesser extent, by 2–4 m M Ca 2+ and Mg 2+. Maturation induced by 1.5 m M Mn 2+ was inhibited by K + concentrations above 0.25 m M. Potassium was inhibitory when added up to 2 hr before germinal vesicle breakdown occurred. In potassium-free media, maturation could be induced by incubation of oocytes under mild alkaline media (pH 8.5–9). A high percentage of medium-sized oocytes (stage IV according to Dumont) was induced to mature by progesterone in the absence of potassium. Maturation of oocytes in potassium-free media was normal by the criteria of germinal vesicle breakdown, production of maturation promoting factor, vitelline membrane activation, and inhibition by known maturation inhibitors.

The effects of barium ions on the spontaneous excitatory post-synaptic potentials in the brain of Helix pomatia (L.)

1. 1. Intracellular methods have been used to study the effects of barium ions on the spontaneous EPSPs of the snail brain. 2. 2. An analysis of the interspike interval histograms of various pacemaker neurones showed characteristic differences when pacemaker activity and/or EPSPs were influenced in the barium media. 3. 3. The steady-state membrane resistance decreased when slow or fast EPSPs were evoked. The slope membrane resistance increased in some neurones while it decreased when the synaptically evoked effects of the barium ions predominated. 4. 4. The amplitude and frequency of the spontaneous fast and slow EPSPs increased when barium acted. 5. 5. The spontaneous EPSPs were not unequivocally prevented in 0 Ca 2+-30mM Mg 2+ medium. but they were highly depressed in some cases, and were again facilitated in the presence of Ba 2+ 6. 6. Na +-free (Tris or Choline) solution totally blocked the barium evoked spontaneous EPSPs, but after readmission of the sodium ions a facilitation of the transmitter release occurred. The delayed release was also increased if barium had been acting previously in the Na +-free medium. 7. 7. On the other hand K +-free solution increased the spontaneous transmitter release, and the facilitatory effect of barium ions was enhanced in the absence of potassium ions. 8. 8. Indirect and/or direct facilitatory effects of barium ions were involved in the spontaneous transmitter release depending on the doses used.

Titration of cyanide and hexacyanoferrate(II) with silver nitrate—I: Calculation of titration curves for potentiometric and conductometric titration

Stepwise potentiometric titration of cyanide and hexacyanoferrate(II) with silver nitrate is possible in the absence of potassium ions. At an initial concentration below 5.00 × 10 −4 M, cyanide can be titrated with silver nitrate (Ag:CN = 1:2) and the end-point indicated by precipitation of silver hexacyanoferrate(II); hexacyanoferrate(II) can be titrated with silver nitrate (Ag: Fe(CN) 6 = 4:1) and the end-point indicated by precipitation of silver dicyanoargentate. The hexacyanoferrate(II) reacts with silver to form two poorly soluble salts, Ag 4Fe(CN) 6, KAg 3Fe(CN) 6. The formation of these salts has been confirmed by conductometric titration of hexacyanoferrate(II) with silver nitrate in solutions containing varying concentrations of potassium nitrate.

Regulation of pyruvate kinases from Fusarium oxysporum.

Two types of pyruvate kinases were found in Fusarium oxysporum. One type (inducible) was present mainly during the early stages of growth on glucose or sucrose and displayed Michaelis-Menten kinetics with respect to phosphoenolpyruvate and adenosine diphosphate. The major type (constitutive) was present under all conditions of growth and displayed in the absence of potassium ions, a sigmoidal substrate saturation curve when phosphoenolpyruvate was used as the variable substrate. In the presence of potassium ions the saturation curve for phosphoenolpyruvate exhibits a plateau at half-maximal velocity. The effects of various metabolites on the activity of the inducible and constitutive kinases were also studied. Fructose-1,6-diphosphate, cyclic AMP, acetyl CoA, tryptophan, and phenylalanine had no effect on the activity of the enzymes. Citrate was a potent inhibitor of the constitutive pyruvate kinase activity and increased the sigmoidicity of the saturation curve for phosphoenolpyruvic acid. In the presence of K+, the bimodal plot observed in the absence of citrate gradually changed to a hyperbolic shape as the concentration of citric acid was increased. In the presence of K+ and ADP as the variable substrate citric acid converted the hyperbolic plot to a sigmoidal one. Citrate had no effect on the inducible enzyme.

The recBC enzyme of Escherichia coli K12: premature cessation of catalytic activities in vitro and reactivation by potassium ions.

It is shown that in vitro the degradation of native and single-stranded DNA as well as the hydrolysis of ATP by purified recBC enzyme ceases 2-3 min after the start of the reaction. The presence of potassium ions (60-100 mM), bovine serum albumin (1 mg/ml) or protein from cell-free Escherichia coli extract (10 microgram/ml) prevents the cessation of the activity. Once the cessation has occurred, the activity of the enzyme can be completely restored by the addition of potassium ions, but not by bovine serum albumin. Sedimentation studies revealed that, in contrast to the active recBC enzyme, the 'silent' enzyme is no longer associated with substrate DNA of high molecular weight. On the basis of these results and other observations it is hypothesized that during the degradation of DNA in the absence of potassium ions or bovine serum albumin the recBC enzyme is subject to an alteration of its molecular conformation which results in an inactive form.