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1.
Methane formation from H2 and CO2 in methanogenic bacteria is a Na+-dependent process. In this communication the effects of Na+ ionophores, of uncouplers, and of Na+/H+ antiporter inhibitors on methane formation from H2 and CO2 were studied with Methanobacterium thermoautotrophicum.
- Na+ ionophores (the Na+/H+ antiporters monensin and lasalocid and the Na+ uniporter gramicidin) stimulated methanogenesis at lwo external Na+ concentrations when the K+ concentration was high. The ionophores had no effect at high external Na+ concentrations and were inhibitory at low external K+ concentrations.
- Uncouplers (protonophores and valinomycin plus K+) inhibited methanogenesis at low external Na+ concentration at both low and high external K+ concentrations. Inhibition by uncouplers was relieved by the addition of either Na+ or Na+ ionophores.
- Na+/H+ antiporter inhibitors (harmaline, amiloride, and NH 4 + ) inhibited methanogenesis at low external Na+ concentration. Inhibition was relieved by the addition of either Na+ or of the Na+ ionophores.
2.
Ijeoma E. Obi Kenneth M. Sterling Gregory A. Ahearn 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2013,183(1):61-69
The effects of sodium, potassium, sugar inhibitors, and membrane potential on 3H-d-glucose uptake by hepatopancreatic epithelial brush border membrane vesicles (BBMV) of the Atlantic marine shrimp, Litopenaeus setiferus, were investigated. Brush border membrane vesicles were prepared using a MgCl2/EGTA precipitation method and uptake experiments were conducted using a high speed filtration technique. 3H-d-Glucose uptake was stimulated by both sodium and potassium and these transport rates were almost doubled in the presence of an inside-negative-induced membrane potential. Kinetics of 3H-d-glucose influx were hyperbolic functions of both external Na+ or K+, and an induced membrane potential increased influx J max and lowered Km in both salts. 3H-d-Glucose influx versus [glucose] in both Na+ or K+ media also displayed Michaelis–Menten properties that were only slightly affected by induced membrane potential. Phloridzin was a poor inhibitor of 0.5 mM 3H-d-glucose influx, requiring at least 5 mM in NaCl and 10 mM in KCl to significantly reduce hexose transport. Several sugars (d-galactose, α-methyl-d-gluco-pyranoside, unlabeled d-glucose, d-fructose, and d-mannose) were used at 75 mM as potential inhibitors of 0.1 mM 3H-d-glucose influx. Only unlabeled d-glucose, d-fructose, and d-mannose significantly (p < 0.05) reduced labeled glucose transport. An additional experiment using increasing concentrations of d-mannose (0, 10, 25, 75, and 100 mM) showed this hexose to be an effective inhibitor of 0.1 mM 3H-d-glucose uptake at concentrations of 75 mM and higher. As a whole these results suggest that 3H-d-glucose transport by hepatopancreatic BBMV occurs by a carrier system that is able to use both Na+ and K+ as drivers, is enhanced by membrane potential, is relatively refractory to phloridzin, and is only inhibited by itself, d-fructose, and d-mannose. These properties are similar to those exhibited by the mammalian SLC5A9/SGLT4 transporter, suggesting that an invertebrate analogue of this protein may occur in shrimp. 相似文献
3.
Ada Duka Gregory A. Ahearn 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2013,183(6):763-771
Hepatopancreatic brush border membrane vesicles (BBMV), made from Atlantic White shrimp (Litopenaeus setiferus), were used to characterize the transport properties of 3H-l-leucine influx by these membrane systems and how other essential amino acids and the cations, sodium and potassium, interact with this transport system. 3H-l-leucine uptake by BBMV was pH-sensitive and occurred against transient transmembrane concentration gradients in both Na+- and K+-containing incubation media, suggesting that either cation was capable of providing a driving force for amino acid accumulation. 3H-l-leucine uptake in NaCl or KCl media were each three times greater in acidic pH (pH 5.5) than in alkaline pH (pH 8.5). The essential amino acid, l-methionine, at 20 mM significantly (p < 0.0001) inhibited the 2-min uptakes of 1 mM 3H-l-leucine in both Na+- and K+-containing incubation media. The residual 3H-l-leucine uptake in the two media were significantly greater than zero (p < 0.001), but not significantly different from each other (p > 0.05) and may represent an l-methionine- and cation-independent transport system. 3H-l-leucine influxes in both NaCl and KCl incubation media were hyperbolic functions of [l-leucine], following the carrier-mediated Michaelis–Menten equation. In NaCl, 3H-l-leucine influx displayed a low apparent K M (high affinity) and low apparent J max, while in KCl the transport exhibited a high apparent K M (low affinity) and high apparent J max. l-methionine or l-phenylalanine (7 and 20 mM) were competitive inhibitors of 3H-l-leucine influxes in both NaCl and KCl media, producing a significant (p < 0.01) increase in 3H-l-leucine influx K M, but no significant response in 3H-l-leucine influx J max. Potassium was a competitive inhibitor of sodium co-transport with 3H-l-leucine, significantly (p < 0.01) increasing 3H-l-leucine influx K M in the presence of sodium, but having negligible effect on 3H-l-leucine influx J max in the same medium. These results suggest that shrimp BBMV transport 3H-l-leucine by a single l-methionine- and l-phenylalanine-shared carrier system that is enhanced by acidic pH and can be stimulated by either Na+ or K+ acting as co-transport drivers binding to shared activator sites. 相似文献
4.
Aleksandra Rašić-Marković Olivera Stanojlović Dragan Hrnčić Danijela Krstić Mirjana Čolović Veselinka Šušić Tatjana Radosavljević Dragan Djuric 《Molecular and cellular biochemistry》2009,327(1-2):39-45
Hyperhomocysteinemia is associated with various pathologies including cardiovascular disease, stroke, and cognitive dysfunctions. Systemic administration of homocysteine can trigger seizures in animals, and patients with homocystinuria suffer from epileptic seizures. Available data suggest that homocysteine can be harmful to human cells because of its metabolic conversion to homocysteine thiolactone, a reactive thioester. A number of reports have demonstrated a reduction of Na+/K+-ATPase activity in cerebral ischemia, epilepsy and neurodegeneration possibly associated with excitotoxic mechanisms. The aim of this study was to examine the in vivo effects of d,l-homocysteine and d,l-homocysteine thiolactone on Na+/K+- and Mg2+-ATPase activities in erythrocyte (RBC), brain cortex, hippocampus, and brain stem of adult male rats. Our results demonstrate a moderate inhibition of rat hippocampal Na+/K+-ATPase activity by d,l-homocysteine, which however expressed no effect on the activity of this enzyme in the cortex and brain stem. In contrast,d,l-homocysteine thiolactone strongly inhibited Na+/K+-ATPase activity in cortex, hippocampus and brain stem of rats. RBC Na+/K+-ATPase and Mg2+-ATPase activities were not affected by d,l-homocysteine, while d,l-homocysteine thiolactone inhibited only Na+/K+-ATPase activity. This study results show that homocysteine thiolactone significantly inhibits Na+/K+-ATPase activity in the cortex, hippocampus, and brain stem, which may contribute at least in part to the understanding of excitotoxic and convulsive properties of this substance. 相似文献
5.
V. A. Belyaev M. M. Dubrovin A. A. Terent’ev A. E. Trenin G. V. Sholin 《Plasma Physics Reports》2001,27(12):1032-1038
The effective cross section for the H 2 + +H 2 + → H 3 + +p reaction in the energy range 5.7–11.5 eV is measured by the split beam method. The maximum of the cross section at an energy of ~8 eV is related to the production of the H 4 ++ compound system. The reaction threshold W thr≈5 eV provides evidence in favor of the classical model of the H 2 + ion with the charge fixed on one of the nuclei throughout the collision event. 相似文献
6.
Chris M. Wood Lisa M. Robertson Ora E. Johannsson Adalberto Luis Val 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2014,184(7):877-890
Mechanisms of Na+ uptake, ammonia excretion, and their potential linkage were investigated in three characids (cardinal, hemigrammus, moenkhausia tetras), using radiotracer flux techniques to study the unidirectional influx (J in), efflux (J out), and net flux rates (J net) of Na+ and Cl?, and the net excretion rate of ammonia (J Amm). The fish were collected directly from the Rio Negro, and studied in their native “blackwater” which is acidic (pH 4.5), ion-poor (Na+, Cl? ~20 µM), and rich in dissolved organic matter (DOM 11.5 mg C l?1). J in Na , J in Cl , and J Amm were higher than in previous reports on tetras obtained from the North America aquarium trade and/or studied in low DOM water. In all three species, J in Na was unaffected by amiloride (10?4 M, NHE and Na+ channel blocker), but both J in Na and J in Cl were virtually eliminated (85–99 % blockade) by AgNO3 (10?7 M). A time course study on cardinal tetras demonstrated that J in Na blockade by AgNO3 was very rapid (<5 min), suggesting inhibition of branchial carbonic anhydrase (CA), and exposure to the CA-blocker acetazolamide (10?4 M) caused a 50 % reduction in J in Na .. Additionally, J in Na was unaffected by phenamil (10?5 M, Na+ channel blocker), bumetanide (10?4 M, NKCC blocker), hydrochlorothiazide (5 × 10?3 M, NCC blocker), and exposure to an acute 3 unit increase in water pH. None of these treatments, including partial or complete elimination of J in Na (by acetazolamide and AgNO3 respectively), had any inhibitory effect on J Amm. Therefore, Na+ uptake in Rio Negro tetras depends on an internal supply of H+ from CA, but does not fit any of the currently accepted H+-dependent models (NHE, Na+ channel/V-type H+-ATPase), or co-transport schemes (NCC, NKCC), and ammonia excretion does not fit the current “Na+/NH4 + exchange metabolon” paradigm. Na+, K+-ATPase and V-type H+-ATPase activities were present at similar levels in gill homogenates, Acute exposure to high environmental ammonia (NH4Cl, 10?3 M) significantly increased J in Na , and NH4 + was equally or more effective than K+ in activating branchial Na+,(K+) ATPase activity in vitro. We propose that ammonia excretion does not depend on Na+ uptake, but that Na+ uptake (by an as yet unknown H+-dependent apical mechanism) depends on ammonia excretion, driven by active NH4 + entry via basolateral Na+,(K+)-ATPase. 相似文献
7.
V. A. Belyaev M. M. Dubrovin A. A. Terent'ev A. E. Trenin G. V. Sholin 《Plasma Physics Reports》2001,27(10):901-903
The effective cross section for the H 2 + + H 2 + → H 3 + + p reaction in the energy range 5.7–11.5 eV is measured by the split beam method. The cross-section maximum at an energy of ~8 eV is related to the production of the H 4 ++ compound system. The reaction threshold W thr ≈5 eV provides evidence in favor of the classical model with the H 2 + ion charge fixed on one of the two nuclei during the entire collision event. 相似文献
8.
Boris N. Kholodenko 《Journal of bioenergetics and biomembranes》1993,25(3):285-295
Kinetic models of the F0F1-ATPase able to transport H+ or/and Na+ ions are proposed. It is assumed that (i) H+ and Na+ compete for the same binding sites, (ii) ion translocation through F0 is coupled to the rate-limiting step of the F1-catalyzed reaction. The main characteristics of the dependences of ATP synthesis and hydrolysis rates on Δφ, ΔpH, and ΔpNa are predicted for various versions of the coupling model. The mechanism of the switchover from \(\Delta \bar \mu _{H^ + } \) -dependent synthesis to the \(\Delta \bar \mu _{Na^ + } \) -dependent one is demonstrated. It is shown that even with a drastic drop in \(\Delta \bar \mu _{H^ + } \) , ATP hydrolysis by the proton mode of catalysis can be effectively inhibited by Δφ and ΔpNa. The results obtained strongly support the possibility that the same F0F1-ATPase in bacterial cells can utilize both \(\Delta \bar \mu _{H^ + } \) and \(\Delta \bar \mu _{Na^ + } \) for ATP synthesis underin vivo conditions. 相似文献
9.
We show that the voltage-gated K+ and Ca2+ currents of rat osteoblastic cells are strongly modulated by arachidonic acid (AA), and that these modulations are very sensitive to the AA concentration. At 2 or 3 μm, AA reduces the amplitude and accelerates the inactivation of the K+ current activated by depolarization; at higher concentrations (≥5 μm), AA still blocks this K+ current, but also induces a very large noninactivating K+ current. At 2 or 3 μm, AA enhances the T-type Ca2+ current, close to its threshold of activation, whereas at 10 μm, it blocks that current. AA (1–10 μm) also blocks the dihydropyridine-sensitive L-type Ca2+ current. Thus, the effect of AA on Ca2+ entry through voltage-gated Ca2+ channels can change qualitatively with the AA concentration: at 2 or 3 μm, AA will favor Ca2+ entry through T channels, both by lowering the voltage-gated K+ conductance and by increasing the T current, whereas at 10 μm, AA will prevent Ca2+ entry through voltage-gated Ca2+ channels, both by inducing a K+ conductance and by blocking Ca2+ channels. 相似文献
10.
This paper represents H+ circles through the bacterial membranes, their peculiarities and relationship with ATP synthesis or hydrolysis, utilization or accumulation of energy are considered. Data on passive and active proton (H+) fluxes through the bacterial membranes are analyzed and their relationship with membrane H+ conductance $\left( {G_m^{H^ + } } \right)$ and permeability for H+ $\left( {P_{H^ + } } \right)$ is discussed. Methods for determination of bacterial membrane $G_m^{H^ + }$ are presented and some difficulties in obtaining and interpreting data are pointed out. Different ways and mechanisms of passive and active H+ fluxes, including a role of membrane lipids in H+ transfer, importance of phase transitions in lipid bilayers, operation of protonophores as well as H+ translocation via the F0 factor of the F0F1-ATPase, are discussed. Dependence of $G_m^{H^ + }$ for Escherichia coli, Enterococcus hirae, Streptococcus lactis and other bacteria on some external physico-chemical growth factors, particularly, on pH and oxidation reduction potential as well as influence of osmotic stress on $G_m^{H^ + }$ and H+ active fluxes through the bacterial membrane under fermentation have been shown. The relationship between $G_m^{H^ + }$ , $P_{H^ + }$ and active H+ fluxes through a membrane is proposed, possible mechanisms of relationship between their alterations depending on pH and oxidation reduction potential are discussed. The results are important for understanding the structural and functional properties of bacterial membranes determining H+ cycles operation and mechanisms of H+ fluxes essential in adaptation of bacteria to altered environment conditions. 相似文献
11.
Wen-zheng Xu Fu-de Ren Jun Ren Sheng-nan Liu Yuan Yue Wen-liang Wang Shu-sen Chen 《Journal of molecular modeling》2010,16(4):615-627
The nature of the unusual cation–π interactions between cations (H+, Li+, Na+, Be2+ and Mg2+) and the electron-deficient B=B bond of the triplet state HB=BH ( $ {}^3\Sigma_g^{-} $ ) was investigated using UMP2(full) and UB3LYP methods at 6–311++G(2df,2p) and aug-cc-pVTZ levels, accompanied by a comparison with 1:1 and 2:1 σ-binding complexes between BH and the cations. The binding energies follow the order HB=BH...H+ > HB=BH...Be2+ > HB=BH...Mg2+ ? HB=BH...Li+ > HB=BH...Na+ and HB=BH (1Δg)...M+/M2+ > H2C=CH2...M+/M2+ > HC≡CH...M+/M2+ > HB=BH ( $ {}^3\Sigma_g^{-} $ )...M+/M2+. Furthermore, except for HB...H+, the σ-binding interaction energy of the 1:1 complex HB...M+/M2+ is stronger than the cation–π interaction energy of the C2H2...M+/M2+, C2H4...M+/M2+, B2H2 (1Δg)...M+/M2+ or B2H2 ( $ {}^3\Sigma_g^{-} $ )...M+/M2+ complex, and, for the 2:1 σ-binding complexes, except for HBBe2+...BH, they are less stable than the cation–π complexes of B2H2 (1Δg) or B2H2 ( $ {}^3\Sigma_g^{-} $ ). The atoms in molecules (AIM) theory was also applied to verify covalent interactions in the H+ complexes and confirm that HB=BH ( $ {}^3\Sigma_g^{-} $ ) can be a weaker π-electron donor than HB=BH (1Δg), H2C=CH2 or HC≡CH in the cation–π interaction. Analyses of natural bond orbital (NBO) and electron density shifts revealed that the origin of the cation–π interaction is mainly that many of the lost densities from the π-orbital of B=B and CC multiple bonds are shifted toward the cations. Figure
The nature of the unusual cation–π interactions between cations (H+, Li+, Na+, Be2+ and Mg2+) and the electron-deficient B=B bond of the triplet state HB=BH ( $ {}^3\Sigma_g^{-} $ ) as investigated using UMP2(full) and UB3LYP methods at 6-311++G(2df,2p) and aug-cc-pVTZ levels 相似文献
12.
The aim of this study was to determine from macroscopic current analysis how intracellular magnesium ions, Mg i 2+ , interfere with sodium channels of mammalian neurones. It is reported here that permeation across the sodium channel is voltage- and concentration-dependently reduced by Mg i 2+ . This results in a general reduction of sodium membrane conductance and an outward sodium peak current at large positive potentials. 30 mM Mg i 2+ leads to a negative shift of voltage dependence of sodium channel gating parameters, probably due to the surface potential change of the membrane. This shift alone is, however, insufficient to explain the reduction of outward sodium currents. The blockage by Mg i 2+ is decreased upon increasing intracellular or extracellular Na+ concentration, which suggests that Mg?' interferes with sodium permeation by competitively occupying sodium channels. Using a kinetic model to describe the sodium permeation, the dissociation constant (at zero membrane potential) of Mg i 2+ for the sodium channel has been calculated to be 8.65 ± 1.51 mM, with its binding site located at 0.26 ± 0.05 electrical distance from the inner membrane. This dissociation constant is smaller than that of Na i +, which is 83.76 ± 7.60 mM with its binding site located at 0.75 ± 0.23. The low dissociation constant of Mg i 2+ reflects its high affinity for the sodium channel. 相似文献
13.
14.
N. N. Rodionova E. Z. Bibineyshvili A. R. Brazhe A. I. Yusipovich G. V. Maksimov A. B. Rubin 《Biophysics》2014,59(1):83-85
Using Raman spectrometry and fluorescence microscopy, we studied the rearrangement of carotenoid molecules and membrane-bound Ca mb 2+ in myelinated nerve fibers after K+ depolarization, K+-channel blocking, and altering the membrane protein conformation. We observed a decrease in Ca mb 2+ and an increase of microviscosity in myelin after depolarization. Changes in Ca mb 2+ and microviscosity were registered after blocking the K+ channels and modifying proteins with PCMB. Our results suggest an interconnection between the condition of nerve fiber membrane proteins, Ca mb 2+ distribution, and myelin microviscosity. 相似文献
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16.
I. R. Arenstein C. Caruso-Neves L. F. Onuchic A. G. Lopes 《The Journal of membrane biology》1995,146(1):47-57
The cell volume regulation of the lower segment cells of the Malpighian tubule of Rhodnius neglectus in anisosmotic media was evaluated by using videooptic techniques. When the medium osmolality was increased with addition of 100 mm mannitol the cells shrank to a minimum of 16.84±2.62% and subsequently swelled towards their initial volume undergoing a typical regulatory volume increase (RVI). Replacement of either K+ or Cl? or HCO 3 ? by Na+, gluconate and phosphate, respectively, abolished the RVI response. Furthermore, the substitution of Na+ by tetramethylammonium (TMA+) in isosmotic conditions led to cellular swelling and death. Addition of either amiloride 10?4 m, anthracene-9-COOH 5×10?4 m, furosemide 5×10?4 m or ethacrynic acid 5×10?5 m, also abolished RVI. On the other hand, addition of either Ba2+ 10?3 m, SITS 5× 10?4 m, ouabain 10?3 m or vanadate 10?3 m, did not change the RVI response. When the tubules were incubated in hyperosmotic media with EGTA 2 mm or verapamil 10?6 m, the RVI response was abolished. In contrast, a decrease of NaCl concentration from 129 to 79 mm induced a cell swelling to a maximum of 33.11+1.73%, but the cells maintained swollen, only partially regulating their volume. These results show that the proximal cells of Malpighian tubule of R. neglectus are able to regulate their volume in hyperosmotic but only partially regulating in hyposmotic solutions. The mechanisms in RVI involve Na+, K+, Cl?, Ca2+ and HCO 3 ? transport pathways and a ouabain-insensitive ATPase stimulated by Na+. This work was supported by grants from the Fundação de Amparo à Pesquisa do Estado de São Paulo—FAPESP; Conselho Nacional de Desenvolvimento Científico e Tecnológico—CNPq e Financiadora de Projetos e Pesquisas-FINEP. 相似文献
17.
The uptake of glycine,l-aspartic acid andl-lysine at pH 5 was not systematically affected by the presence of up to 0.1m NaCl or KCl, without or with 0.3mm actidione. The observed effects, either positively or negatively altering the rate of amino acid uptake, depended on the concentration of the ion but were always qualitatively the same for Na+ and K+. The inhibition prevailing with 0.1m ions was significantly more pronounced with Na+ than with K+. The presence of other anions (phosphate, nitrate, sulphate) had a slight but significant effect on uptake as compared with the variant using chloride. It is concluded that inSaccharomyces cerevisiae the transport of amino acids is not essentially coupled with the transport of different ions. 相似文献
18.
19.
Ulrich Kragh-Hansen Karl Evald J?rgensen M. Iqbal Sheikh 《The Biochemical journal》1982,208(2):359-368
Renal transport of four different categories of organic solutes, namely sugars, neutral amino acids, monocarboxylic acids and dicarboxylic acids, was studied by using the potential-sensitive dye 3,3′-diethyloxadicarbocyanine iodide in purified luminal-membrane and basolateral-membrane vesicles isolated from rabbit kidney cortex. Valinomycin-induced K+ diffusion potentials resulted in concomitant changes in dye–membrane-vesicle absorption spectra. Linear relationships were obtained between these changes and depolarization and hyperpolarization of the vesicles. Addition of d-glucose, l-phenylalanine, succinate or l-lactate to luminal-membrane vesicles, in the presence of an extravesicular>intravesicular Na+ gradient, resulted in rapid transient depolarization. With basolateral-membrane vesicles no electrogenic transport of d-glucose or l-phenylalanine was observed. Spectrophotometric competition studies revealed that d-galactose is electrogenically taken up by the same transport system as that for d-glucose, whereas l-phenylalanine, succinate and l-lactate are transported by different systems in luminal-membrane vesicles. The absorbance changes associated with simultaneous addition of d-glucose and l-phenylalanine were additive. The uptake of these solutes was influenced by the presence of Na+-salt anions of different permeabilities in the order: Cl−>SO42−>gluconate. Addition of valinomycin to K+-loaded vesicles enhanced uptake of d-glucose and l-phenylalanine in the presence of an extravesicular>intravesicular Na+ gradient. Gramicidin or valinomycin plus nigericin diminished/abolished electrogenic solute uptake by Na+- or Na++K+-loaded vesicles respectively. These results strongly support the presence of Na+-dependent renal electrogenic transport of d-glucose, l-phenylalanine, succinate and l-lactate in luminal-membrane vesicles. 相似文献
20.
Biofortification of rice grain with zinc through zinc fertilization in different countries 总被引:5,自引:0,他引:5
N. Phattarakul B. Rerkasem L. J. Li L. H. Wu C. Q. Zou H. Ram V. S. Sohu B. S. Kang H. Surek M. Kalayci A. Yazici F. S. Zhang I. Cakmak 《Plant and Soil》2012,358(1-2):131-141