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1.
The crystal structure of potassium hydroxide complexed amylose, obtained by heterogeneous deacetylation of amylose triacetate, has been determined through a combined stereochemical structure-refinement and X-ray diffraction-analysis. The structure crystallizes in an orthorhombic unit-cell with parameters a 8.84, b 12.31, and c (fiber repeat) 22.41 Å, and with P212121 symmetry. The conformation of the amylose chain is a distorted, left-handed helix with 6 d-glucose residues per turn. Each three-residue asymmetric unit is complexed with one molecule of potassium hydroxide and three molecules of water. The K+ ion coordinates with four oxygen atoms of the amylose chain and with two other oxygen atoms, and this coordination is probably the cause for the more-extended amylose chain-conformation than would be predicted from a φ, ψ map. The distortions in the chain are primarily manifested by different O-6 rotations and by slightly different bridge and φ, ψ angles for the individual residues. The structure is extensively hydrogen bonded, although largely through water molecules, which accounts for its ready water solubility. The left-handed conformation of the chain in this structure is consistent with the conformations of amylose triacetate and V-amylose, both of which are left-handed. 相似文献
2.
A simple procedure is described for the assay of phosphorylation using C?erenkov radiation to detect 32P in a liquid scintillation counter. Unreacted 32Pi is first removed from the reaction mixture as the phosphomolybdate complex by butanol/benzene extraction. Addition of ammonium hydroxide to the remaining aqueous fraction avoids color quenching, phase separation, and instability in the counting rate during measurement of 32P. Application of this procedure to several photophosphorylation systems is included. 相似文献
3.
The transport of protons and potassium ions across the membranes of the bacteria Enterococcus hirae growing in an alkaline medium (pH 8.0) or under experimental conditions (pH 7.5) during glucose fermentation accomplished
by a KtrI system of absorption of potassium ions, which can interact with F0F1-ATPase to form at H+-K+-pump, has been studied. It was found on cells with a high membrane permeability that the administration of nicotinamide adenine
dinucleotides results in the potassium absorption which is insensitive to the inhibitor of F0F1-ATPase N,N′-dicyclohexylcarbodiimide. It is assumed that, along with the KtrI system which interacts with F0F1-ATPase, a separate KtrI or another K+ absorption system operates in these bacteria under particular conditions, which is dependent on NAD+ +NADH. Presumably, these interact with this system, changing its conformational state required for the transition to the
“active” form. 相似文献
4.
Juan A. Cooper Steven J. Haylock Leonard F. Blackwell Paul D. Buckley 《Inorganica chimica acta》1985,106(4):223-227
The mixture of chromium, nicotinic acid and the amino acids glycine, glutamic acid and cysteine which stimulates the rate of CO2 production in a yeast bioassay system was subjected to the separation scheme based on ion-exchange chromatography which has been used to separate the chromium- containing fractions in brewer's yeast, [S.J. Haylock, P.D. Buckley and L.F. Blackwell, J. Inorg. Biochem., 18, 195 (1983)]. Four chromium-containing fractions (C2 to C5) were obtained by salt gradients and two further fractions (G1 and G2) were obtained using a pH gradient. All were amino acid-containing complexes of chromium and all except C5 also contained nicotinic acid. However, none of the isolated chromium fractions showed any activity in a yeast bioassay. On the basis of previous work, the activity of the original mixture was attributed to the presence of an oxygen-coordinated trans chromium(III)-dinicotinate complex. Biologically- inactive chromium complexes such as Cr(glu)2(H2O)+2 and Cr(gly)2(H2O)+2 after elution by ammonium hydroxide from Dowex 50W-X12 cation- exchange columns, stimulated the rate of CO2 production in the yeast bioassay. Elution with other bases, such as lithium hydroxide, potassium hydroxide and sodium hydroxide led to inactive fractions in all cases. A warning is therefore given that the use of ammonium hydroxide-elution of ion-exchange columns to isolate glucose tolerance factor fractions from biological samples (such as brewer's yeast) can lead to active fractions which do not relate to the native material. 相似文献
5.
Ankur Srivastava Gargi Mishra Kshitij RB Singh Jay Singh Rampal Pandey Mrituanjay D. Pandey 《Luminescence》2023,38(7):1347-1357
Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4-N,N-dimethylaminobenzoate-κO)(μ2–4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La2O3 nanomaterials to obtain a nanohybrid La2O3/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and 1H and 13C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La2O3/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La2O3/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour. 相似文献
6.
Suryabhan Singh 《Inorganica chimica acta》2011,367(1):230-232
Compounds of the type R3SnSH are believed to be unstable (unless sterically protected by very bulky R groups) because of their facile condensation into the corresponding sulfide, (R3Sn)2S. One such compound, Ph3SnSH has been synthesized by an one pot reaction of triphenyltin hydroxide with thiophosgene followed by the hydrolysis of the intermediate triphenyltin chlorothioformate. The product, triphenyltin hydrosulfide has been characterized by IR, 1H, 13C and 119Sn NMR spectral techniques. Single crystal X-ray analysis revealed that the molecule is a discrete monomer containing tin atom at the centre of a distorted tetrahedron. Plausible reaction mechanism for the formation of the molecule has also been reported. 相似文献
7.
Akopova OV Nosar VI Bouryi VA Mankovskaya IN Sagach VF 《Biochemistry. Biokhimii?a》2010,75(9):1139-1147
The influence of the KATP+-channel opener diazoxide on the K+ cycle and oxygen consumption has been studied in rat liver mitochondria. It was found that diazoxide activates the KATP+-channel in the range of nanomolar concentrations (50–300 nM, K
1/2 ∼ 140 nM), which results in activation of K+/H+ exchange in mitochondria. The latter, in turn, accelerates mitochondrial respiration in respiratory state 2. The contribution
of KATP+-channel to the mitochondrial potassium cycle was estimated using the selective KATP+-channel blocker glibenclamide. The data show that the relative contribution of KATP+-channel in the potassium cycle of mitochondria is variable and increases only with the decrease in the ATP-independent component
of K+ uptake. Possible mechanisms underlying the observed phenomena are discussed. The experimental results more fully elucidate
the role of KATP+-channel in the regulation of mitochondrial functions, especially under pathological conditions accompanied by impairment
of the mitochondrial energy state. 相似文献
8.
- 1.1. The role of aldosterone on active potassium transport across lizard colon under voltage-clamped conditions has been investigated.
- 2.2. Control colons exhibited no net potassium flux (Jknet) despite of the existence of active opposite unidi ectional fluxes.
- 3.3. An important net secretory potassium flux was found in short-circuited aldosterone-stimulated colons.
- 4.4. Mucosal amiloride did not change (Jknet) either in control or aldosterone-stimulated colons.
- 5.5. Luminal barium alters K + transport in a manner consistent with the presence of barium-sensitive conductances at the apical membrane of both control and aldosterone-treated colons.
- 6.6. The effects of ouabain and barium on control and aldosterone-induced potassium flows were consistent with a model involving basolateral uptake by an Na +-K +-ATPase and conductive exit across the apical membrane.
- 7.7. The stimulatory effect of aldosterone on potassium secretion is associated with parallel increases of both basolateral K + entry and the apical conductive pathway.
9.
Glass AD 《Plant physiology》1980,65(1):160-164
Potassium influx isotherms were obtained for 10 cultivars of barley using plants which had been grown with or without potassium (high K+ and low K+ plants, respectively), and the cultivars ranked with respect to Km or Vmax values for influx with a view to using these rankings as a predictive measure of long term performance under conditions of potassium-limited growth. Analyses of these rankings revealed significant differences between cultivars. Net uptake rates for low K+ plants, determined over a 24-hour period, confirmed the differences between upper (Herta) and lower (Conquest) ranked cultivars, and established similar differences in the rates of translocation to the shoot. Efflux analyses showed no differences in potassium efflux from the cytoplasm or from the vacuole for these cultivars. Growth rate studies under different conditions of potassium limitation indicated, with some exceptions, strong positive correlations between ranks accorded cultivars on the basis of influx kinetics and those based upon growth rates. 相似文献
10.
《Comparative biochemistry and physiology. A, Comparative physiology》1994,107(4):949-956
Na+-dependent leucine uptake was greater in potassium loaded brush-border membrane vesicles compared with controls. This effect was not mediated by an electrical potential difference, since it was still present in voltage-clamped conditions. Inhibition experiments indicate the same Na+-dependent leucine transport activity in the presence or in the absence of potassium. The affinity of sodium for the cotransporter was identical at 10 or 100 mM potassium. Leucine kinetics at different potassium concentrations showed a maximum 2.4-fold increase in Vmax, while Km was unaffected. The secondary plots of the kinetic results were not linear. This kinetic behaviour suggests that K+ acts as a non-essential activator of Na+-dependent leucine cotransport. A charge compensation of sodium-leucine influx is most probably a component of the potassium effect in the presence of valinomycin. 相似文献
11.
Lithium (Li+) has been used in the treatment of manic—depressive disorders for several decades. More recently, Li+ has been shown to affect the signaling pathway of various neurotransmitters and growth/neurotrophic factors. We examined the effect of Li+ on the survival of cerebellar granule neurons in culture. Treatment of immature granule cells with Li+ resulted in programmed cell death (apoptosis). The death process is accompanied by DNA fragmentation, a hallmark of apoptosis. Following maturation in vitro, granule neurons are dependent on elevated concentrations of extracellular potassium ([K+]o) for survival. Lowering of [K+]o to physiological levels induces apoptosis. Surprisingly, Li+ prevents death of mature neurons caused by low [K+]o. Moreover, the concentration range at which Li+ exerts its protective effect is the same as that at which it induces apoptosis in immature neurons. Thus, a single agent under similar extracellular conditions has opposing effects on survival, depending on the developmental status of the neuron. 相似文献
12.
13.
Wolfram Nagel Mary Beth Pope Kim Peterson Mortimer M. Civan 《The Journal of membrane biology》1980,57(3):235-241
Summary Skins from the frogRana pipiens pipiens were studied under short-circuited conditions during the course of removing and replacing potassium in the inner bathing media in 14 experiments. The intracellular potential (V
SC), fractional resistance (FR), short-circuit current (I
SC) and total tissue conductance (g
T) were constantly monitored during impalements of the epithelial cells. The mean value (±se) forV
SC was –79 (±3) mV under baseline conditions. Removal of potassium from the inner bathing solution transiently stimulated the short-circuit current and hyperpolarized the basolateral membrane; with sufficiently long incubations, the basolateral membrane was eventually depolarized. Restoration of potassium to the inner solution within 43 min after initiating the perfusion with K+-free solution depolarized the basolateral membrane. However, restoration of potassium after at least 11/2 hr of incubation hyperpolarized the membrane. Ouabain consistently depolarized the basolateral membrane, even after extended periods of potassium depletion as long as 320 min. In the presence of ouabain, restoration of potassium depolarized the basolateral membrane. The data provide further evidence for the concept that the Na–K exchange pump of frog skin is rheogenic. Furthermore, the results suggest that the pump continues to be active even during prolonged periods of potassium depletion, reaccumulating potassium which has leaked out of the epithelial cells. 相似文献
14.
Improved Double-Vial Radiorespirometric Technique for Mineralization of 14C-Labeled Substrates
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New procedures which simplify sample preparation and improve counting efficiency were developed for double-vial radiorespirometry. Under certain conditions, efficiency of fluor-NaOH-impregnated wicks was not stable, but was adversely affected by water vapor, NaOH concentration, and CO2 loading. Glass fiber wick material treated with a methanolic fluor-NaOH solution showed improved 14C counting efficiency (58%) compared with previous methods. 相似文献
15.
The viscosities of concentrated solutions of sodium and potassium halides (concentration range 0.125 to 3.0m) have been measured in aqueous maltose solution at 25, 30, 35, and 40°. Various equations employed for concentrated solutions of electrolytes have been tested, to ascertain the validity of the relative viscosity data. In order to elucidate the structural behavior of sodium and potassium halides in aqueous maltose solution, the molar volumes (), ionic B-coefficients, and hydration numbers (nB) of various ions have been computed. The B+ and B? coefficients have been interpreted in terms of solute-solvent interactions. On the basis of the data, it has been found that, in 0.5m maltose solution, the different ions show structure-breaking tendency in the order: I? > Br? > Cl? > K+ > Na+. 相似文献
16.
Measurements of the potassium current in the squid axon membrane have been made, after changes of the membrane potential to the sodium potential of Hodgkin and Huxley (HH), from near the resting potential, from depolarizations of various durations and amplitudes, and from hyperpolarizations of up to 150 mv. The potassium currents I given by I = I∞ {1 - exp [- (t + t0)/τ]}25, where t0 is determined by the initial conditions, represent the new data and approximate the HH functions in the regions for which they are adequate. A corresponding modification for the sodium current does not appear necessary. The results support the HH assumptions of the independence of the potassium and sodium currents, the dependence of the potassium current upon a single parameter determined by the membrane potential, and the expression of this parameter by a first order differential equation, and, although the results drastically modify the analytical expressions, they very considerably extend the range of apparent validity of these assumptions. The delay in the potassium current after severe hyperpolarization is used to estimate a potassium ion mobility in the membrane as 10-5 of its value in aqueous solutions. 相似文献
17.
Three indolyl-imine ligands have been synthesized through the condensation of S-benzyldithiocarbazate with indole-2-carbaldehyde, indole-3-carbaldehyde and indole-7-carbaldehyde. Treatment of these Schiff bases with acetate salts of Ni(II), Zn(II) and Cd(II) in ethanol yielded a series of complexes of 2:1 type (ligand/metal ratio) in which the ligands coordinated to the metal ions as monoanionic NS bidentate chelates. While the 2-imineindole and 3-imineindole formed the expected five-membered chelate rings, the X-ray crystal structure of [Cd(HL3)(py)2], (HL3 = the mono-deprotonated 7-imineindole), revealed an unusual mode of coordination, namely formation of four-membered rings with the metal atom. Reaction of the 7-imineindole with the metal ions in the presence of potassium hydroxide produced complexes of the type [M(L3)(H2O)] in which the Schiff base acts as a dianionic NNS tridentate ligand. 相似文献
18.
The enamel/saliva interface is mimicked by the comparably much simpler model of (001) surfaces of hydroxy-apatite ( Ca10(PO4)6(OH)2 ) in contact with aqueous solution. At neutral pH, the dissociation of ions is penalized by more than 150 kJ mol-1 giving rise to very stable apatite-water interfaces. This picture changes drastically with decreasing pH, as the protonation
of phosphate and hydroxide ions lowers the free energy of calcium ions dissociation. Our simulations suggest the mechanism
of acid-induced apatite decomposition to i) require a considerable degree of protonation of the apatite surface. The first
ion dissociation step ii) involves calcium ions which electrostatic binding has been locally destabilized through phosphate
and hydroxide protonation. The depletion of calcium ions embedding the anions then allows iii) the dissociation of the anionic
species. Along this line, the protective role of fluoride in caries prevention is related to the stabilization of the calcium
triangles embedding the OH-/F- ions. 相似文献
19.
Continuous monitoring of rhizosphere respiration after labelling of plant shoots with 14CO2 总被引:1,自引:1,他引:0
Nguyen Christophe Todorovic Christine Robin Christophe Christophe Angélique Guckert Armand 《Plant and Soil》1999,212(2):189-199
The present work describes an original method to follow rate of 14CO2 and total CO2 production from rhizosphere respiration after plant shoots had been pulse-labelled with 14CO2. We used a radioactivity detector equipped with a plastic cell for flow detection of beta radiation by solid scintillation
counting. The radioactivity detector was coupled with an infrared gas analyser. The flow detection of 14CO2 was compared to trapping of 14CO2 in NaOH and counting by liquid scintillation. First, we demonstrated that NaOH (1 M) trapped 95% of the CO2 of a gaseous sample. Then, we determined that the counting efficiency of the radioactivity flow cell was 41% of the activity
of gaseous samples as determined by trapping in NaOH (1 M) and by counting by static liquid scintillation. The sensitivity
of the 14CO2- flow detection was 0.08 Bq mL−1 air and the precision was 2.9% of the activity measured compared to 0.9% for NaOH trapping method. We presented two applications
which illustrate the relevance of 14CO2-flow detection to investigations using 14C to trace photoassimilates within the plant-soil system. First, we examined the
kinetics of 14CO2 production when concentrated acid is added to NaH14CO3. This method is the most commonly used to label photoassimilates with 14C. Then, we monitored 14CO2 activity in rhizosphere respiration of 5-week old maize cultivated in soil and whose shoots had been pulse-labelled with
14CO2. We conclude that alkali traps should be used for a cumulative determination of 14CO2 because they are cheap and accurate. On the other hand, we demonstrated that the flow detection of 14CO2 had a finer temporal resolution and was consequently a relevant tool to study C dynamics in the rhizosphere at a short time
scale.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献