scholarly journals Permeability of P and K-nutrient through polystyrene membrane from aqueous solutions of urea + KH2PO4

2018 ◽  
Vol 20 (4) ◽  
pp. 113-122
Author(s):  
Xiaonan Deng ◽  
Kun Liu ◽  
Xiaozhao Han ◽  
Xianguo Hu ◽  
Shufeng Zheng
Keyword(s):  
Diffusion Coefficient ◽  
Release Kinetics ◽  
Ussing Chamber ◽  
Solute Concentration ◽  
Polymer Membrane ◽  
Compound Fertilizer ◽  
Low Concentrations ◽  
Coated Urea ◽  
High Concentrations ◽  
Kinetics Of

Abstract With the polymer-coated fertilizer as background, the permeability of P- and K-nutrient through a representative polymer membrane-polystyrene membrane were investigated by measuring their permeability in the solutions of KH2PO4-water and urea-KH2PO4-water at nominal temperature of 298 K using the Ussing chamber method. To analyze and interpret the variation of permeability with solute concentration, the solubility of permeate in polymer membrane were determined experimentally and the permeate diffusion coefficient were assessed by the measurements of density and apparent molar volume of the aqueous fertilizer solutions. An interesting “increase-decrease” trend for the permeability of both phosphorous (P)-nutrient, and potassium (K)-nutrient fertilizer with permeate concentration was observed, in which the increases in permeability at low concentrations of permeate could be attributed to the increase in solubility of KH2PO4 in polymer while the decreases in permeability at high concentrations was due to the decrease in diffusion coefficient of permeate in polymer membrane. Finally, the release kinetics of these nutrients from a PS-coated urea-KH2PO4 compound fertilizer granule was predicted using the Shaviv’s model along with the permeability data of P- and K-nutrient generated.

scholarly journals Some properties of pyruvate and 2-oxoglutarate oxidation by blowfly flight-muscle mitochondria

1972 ◽  
Vol 127 (1) ◽  
pp. 271-283 ◽  
Author(s):  
R. G. Hansford
Keyword(s):  
Oxygen Uptake ◽  
Isocitrate Dehydrogenase ◽  
Adenine Nucleotides ◽  
Slight Reduction ◽  
Glycerol Phosphate ◽  
Pyruvate Oxidation ◽  
Low Concentrations ◽  
High Concentrations ◽  
Kinetics Of ◽  
Very High

1. High rates of state 3 pyruvate oxidation are dependent on high concentrations of inorganic phosphate and a predominance of ADP in the intramitochondrial pool of adenine nucleotides. The latter requirement is most marked at alkaline pH values, where ATP is profoundly inhibitory. 2. Addition of CaCl2 during state 4, state 3 (Chance & Williams, 1955) or uncoupled pyruvate oxidation causes a marked inhibition in the rate of oxygen uptake when low concentrations of mitochondria are employed, but may lead to an enhancement of state 4 oxygen uptake when very high concentrations of mitochondria are used. 3. These properties are consistent with the kinetics of the NAD-linked isocitrate dehydrogenase (EC 1.1.1.41) from this tissue, which is activated by isocitrate, citrate, ADP, phosphate and H+ ions, and inhibited by ATP, NADH and Ca2+. 4. Studies of the redox state of NAD and cytochrome c show that addition of ADP during pyruvate oxidation causes a slight reduction, whereas addition during glycerol phosphate oxidation causes a `classical' oxidation. Nevertheless, it is concluded that pyruvate oxidation is probably limited by the respiratory chain in state 4 and by the NAD-linked isocitrate dehydrogenase in state 3. 5. The oxidation of 2-oxoglutarate by swollen mitochondria is also stimulated by high concentrations of ADP and phosphate, and is not uncoupled by arsenate.

scholarly journals Kinetics of Alkaline Phosphatase from Pig Kidney. Influence of complexing agents on stability and activity

1976 ◽  
Vol 153 (2) ◽  
pp. 151-157 ◽  
Author(s):  
B P Ackermann ◽  
J Ahlers
Keyword(s):  
Alkaline Phosphatase ◽  
Metal Ion ◽  
Complexing Agents ◽  
Pig Kidney ◽  
Low Concentrations ◽  
Sequential Addition ◽  
Quantitative Examination ◽  
High Concentrations ◽  
Kinetics Of ◽  
Active Centres

Metal ion-complexing agents, like KCN, EDTA etc., inactivate alkaline phosphatase of pig kidney. This inactivation is reversible at low concentrations of the complexing agents and irreversible at high concentrations. The reversible inhibition is probably due to removal of Zn2+ ions from the active site, where they are necessary for catalytic action, whereas the irreversible inhibition results from the removal of Zn2+ ions necessary for preservation of the structure. The inactivation is pseudo-first order. It depends on the concentration, size and charge of the complexing agents. β-Glycerophosphate and Mg2+ ions protect the enzyme from inactivation by complexing agents. Quantitative examination of the effect of substrate leads to a model that is similar to the “sequential model” proposed by D.E. Koshland, G. Nemethy & D. Filmer (1966) (Biochemistry 5, 365-385) to explain allosteric behavior of enzymes. It describes the sequential addition of two substrate molecules at two active centres of the dimer enzyme. The binding of the substrate molecules is accompanied by changes in the conformation, which lead to stabilization of the enzyme against attack by complexing agents.

scholarly journals Steady-state kinetics of catecholamine transport by chromaffin-granule ‘ghosts’

1974 ◽  
Vol 144 (2) ◽  
pp. 319-325 ◽  
Author(s):  
J H Phillips
Keyword(s):  
Steady State ◽  
Competitive Inhibitor ◽  
Affinity Constant ◽  
Chromaffin Granule ◽  
Affinity Constants ◽  
Steady State Kinetics ◽  
Low Concentrations ◽  
High Concentrations ◽  
Chromaffin Granule Ghosts ◽  
Kinetics Of

Resealed chromaffin-granule ‘ghosts’ were used to study the steady-state kinetics of catecholamine transport. The pump has a high affinity for (-)-noradrenaline, (-)-adrenaline, tyramine and 5-hydroxytryptamine (serotonin), but a lower affinity for (+)-noradrenaline. The measured rates of incorporation do not conform to Michaelis–Menten kinetics, but affinity constants for the former substrates are in the range 8–18μm. Reserpine is a potent inhibitor. Incorporation as a function of ATP concentration also fails to show simple kinetics; the affinity constant for ATP is deduced to be about 3mm at 1mm-MgCl2. Adenylyl (βγ-methylene)diphosphonate is a competitive inhibitor at low concentrations, but inhibits more strongly at high concentrations. The pump has a transition temperature at 29°C and does not seem to be identical with the Mg2+-stimulated adenosine triphosphatase of chromaffin granules.

Kinetics of Uptake of Lysine and Lysyl-Lysine by Hamster Jejunum in Vitro

1980 ◽  
Vol 59 (4) ◽  
pp. 285-287 ◽  
Author(s):  
D. Burston ◽  
E. Taylor ◽  
D. M. Matthews
Keyword(s):  
Amino Acid ◽  
Molar Basis ◽  
Low Concentrations ◽  
High Concentrations ◽  
Kinetics Of Uptake ◽  
Kinetics Of

1. The kinetics of 2-min uptake of l-lysine and l-lysyl-l-lysine have been studied by using rings of everted hamster intestine in vitro, and values for Kt and Vmax, established. 2. On a molar basis, mediated uptake was more rapid for the amino acid than for the peptide. Non-mediated uptake was more rapid for the peptide than for the amino acid. 3. Comparison of relative rates of uptake of lysine from equivalent solutions of lysine and lysyl-lysine showed that at low concentrations, uptake of lysine was less rapid from the peptide than from the amino acid, whereas at high concentrations, uptake of lysine was more rapid from the peptide than from the amino acid. This type of effect of concentration on relative rates of uptake from equivalent solutions of amino acid and peptide has not previously been described.

scholarly journals Kinetics of substrate hydrolysis and inhibition by mipafox of paraoxon-preinhibited hen brain esterase activity

1986 ◽  
Vol 236 (2) ◽  
pp. 503-507 ◽  
Author(s):  
C D Carrington ◽  
M B Abou-Donia
Keyword(s):  
Kinetic Parameters ◽  
Organophosphorus Compounds ◽  
Model Fit ◽  
Component Model ◽  
Low Concentrations ◽  
Two Component ◽  
High Concentrations ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Organophosphorus Inhibitor

For the purpose of assessing the neurotoxic potential of organophosphorus compounds, it has been determined that paraoxon-preinhibited hen brain has both neurotoxicant (mipafox)-sensitive (neurotoxic esterase; NTE) and -insensitive esterase components. Several experiments designed to investigate the kinetic parameters governing the reaction of these esterases with two substrates and one organophosphorus inhibitor are presented. First, kinetic parameters for the hydrolysis of phenyl valerate and phenyl phenylacetate were measured. At 37 degrees C, the Km values of NTE for phenyl valerate and phenyl phenylacetate were found to be about 1.4 × 10(-3) and 1.6 × 10(-4) M respectively. At 25 degrees C, the Km of NTE for phenyl valerate was determined to be about 2.4 × 10(-3) M. Secondly, the kinetic constants of NTE for mipafox were measured at both 25 degrees C and 37 degrees C. With either phenyl valerate or phenyl phenylacetate as substrate, the Km at 37 degrees C was determined to be about 1.8 × 10(-4) M, and the phosphorylation constant (k2) was about 1.1 min-1. For phenyl valerate only, the Km at 25 degrees C was found to be about 6 × 10(-4) M, and the k2 was about 0.7 min-1. The data obtained at 25 degrees C were analysed by using a two-component model without formation of Michaelis complex, a two-component model with formation of Michaelis complex on the second component (NTE), or a three-component model without formation of Michaelis complex. The fact that the Michaelis model fit the data significantly better than either of the other two models indicates that the higher apparent Ki values that occur with low concentrations of mipafox are due to formation of Michaelis complex at high concentrations, rather than because of the presence of two NTE isoenzymes, as has been suggested by other investigators.

Zinc-Induced Augmentation of Excitatory Synaptic Currents and Glutamate Receptor Responses in Hippocampal CA3 Neurons

2001 ◽  
Vol 85 (3) ◽  
pp. 1185-1196 ◽  
Author(s):  
Dean D. Lin ◽  
Akiva S. Cohen ◽  
Douglas A. Coulter
Keyword(s):  
Pyramidal Neurons ◽  
Granule Cells ◽  
Mossy Fiber ◽  
Release Kinetics ◽  
Excitatory Synapses ◽  
Hippocampal Ca3 ◽  
Excitatory Neurotransmission ◽  
High Concentrations ◽  
Ca3 Neurons ◽  
Kinetics Of

Zinc is found throughout the CNS at synapses co-localized with glutamate in presynaptic terminals. In particular, dentate granule cells' (DGC) mossy fiber (MF) axons contain especially high concentrations of zinc co-localized with glutamate within vesicles. To study possible physiological roles of zinc, visualized slice-patch techniques were used to voltage-clamp rat CA3 pyramidal neurons, and miniature excitatory postsynaptic currents (mEPSCs) were isolated. Bath-applied zinc (200 μM) enhanced median mEPSC peak amplitudes to 153.0% of controls, without affecting mEPSC kinetics. To characterize this augmentation further, rapid agonist application was performed on perisomatic outside-out patches to coapply zinc with glutamate extremely rapidly for brief (1 ms) durations, thereby emulating release kinetics of these substances at excitatory synapses. When zinc was coapplied with glutamate, zinc augmented peak glutamate currents (mean ± SE, 116.6 ± 2.8% and 143.8 ± 9.8% of controls at 50 and 200 μM zinc, respectively). This zinc-induced potentiation was concentration dependent, and pharmacological isolation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor–mediated currents (AMPAR currents) gave results similar to those observed with glutamate application (mean, 115.0 ± 5.4% and 132.5 ± 9.1% of controls at 50 and 200 μM zinc, respectively). Inclusion of the AMPAR desensitization blocker cyclothiazide in the control solution, however, abolished zinc-induced augmentation of glutamate-evoked currents, suggesting that zinc may potentiate AMPAR currents by inhibiting AMPAR desensitization. Based on the results of the present study, we hypothesize that zinc is a powerful modulator of both excitatory synaptic transmission and glutamate-evoked currents at physiologically relevant concentrations. This modulatory role played by zinc may be a significant factor in enhancing excitatory neurotransmission and could significantly regulate function at the mossy fiber-CA3 synapse.

Uptake of l-valyl-l-Valine and Glycylsarcosine by Hamster Jejunum in Vitro

1982 ◽  
Vol 62 (6) ◽  
pp. 617-626 ◽  
Author(s):  
D. Burston ◽  
R. A. Wapnir ◽  
E. Taylor ◽  
D. M. Matthews
Keyword(s):  
Competitive Inhibition ◽  
Side Chains ◽  
Low Concentrations ◽  
Peptide Component ◽  
High Concentrations ◽  
Kinetics Of Uptake ◽  
Peptide Uptake ◽  
Kinetics Of ◽  
Hydrolysis Of

1. Preliminary observations concerned with the effect of the lipophilic properties of the amino acid side-chains of peptides on their apparent affinity for uptake by rings of everted hamster jejunum showed that of the series glycylglycine, l-alanyl-l-alanine, l-valyl-l-valine and l-leucyl-l-leucine, with increasingly lipophilic side-chains, l-valyl-l-valine, not l-leucyl-l-leucine, was the most powerful inhibitor of uptake of the hydrolysis-resistant dipeptide glycylsarcosine. This apparently anomalous observation indicated a need for further investigation, and this paper reports investigations of the kinetics of uptake of l-valyl-l-valine and of competition for uptake between l-valyl-l-valine and glycylsarcosine. 2. l-Valyl-l-valine was capable of complete competitive inhibition of mediated uptake of glycylsarcosine. Free l-valine did not inhibit mediated uptake of glycylsarcosine. Glycylsarcosine could inhibit mediated uptake of l-valyl-l-valine only partially, but a mixture of glycylsarcosine and l-valine was capable of producing complete inhibition of mediated uptake of l-valyl-l-valine. 3. Investigation of the kinetics of uptake of l-valyl-l-valine indicated two mediated components. Component (a), which disappeared in the presence of free l-leucine, probably represented uptake of free l-valine after hydrolysis of the peptide. Component (b) probably represented peptide uptake. 4. The estimates of Kt obtained for uptake of intact l-valyl-l-valine were many times greater than Ki for inhibition of uptake of glycylsarcosine by l-valyl-l-valine. A possible explanation of the discrepancy is the existence of two pathways for uptake of l-valyl-l-valine and glycylsarcosine, for one of which l-valyl-l-valine has a low Kt (i.e. a high affinity) not readily demonstrable by kinetic analysis. 5. The results suggest that mediated uptake of l-valyl-l-valine is the result of at least two processes, uptake of intact peptide by a mechanism or mechanisms shared with glycylsarcosine and also hydrolysis followed by uptake of free l-valine; estimates of the proportions of intact valine and of free valine taken up by mediated transport suggest that at pH 5 uptake of intact peptide varies from 25% at low concentrations to 55% at high concentrations. They do not explain why l-valyl-l-valine is a stronger inhibitor of uptake of glycylsarcosine than the more lipophilic l-leucyl-l-leucine, but do suggest how such a situation could arise.

Kinetics of Various 99mTc-Sn-Pyrophosphate Compounds in the Rat

1977 ◽  
Vol 16 (04) ◽  
pp. 157-162 ◽  
Author(s):  
C. Schümichen ◽  
B. Mackenbrock ◽  
G. Hoffmann
Keyword(s):  
Normal Saline ◽  
Half Life ◽  
Compound A ◽  
Short Half Life ◽  
Low Concentrations ◽  
The Stability ◽  
Kinetics Of ◽  
In Vitro Stability

SummaryThe bone-seeking 99mTc-Sn-pyrophosphate compound (compound A) was diluted both in vitro and in vivo and proved to be unstable both in vitro and in vivo. However, stability was much better in vivo than in vitro and thus the in vitro stability of compound A after dilution in various mediums could be followed up by a consecutive evaluation of the in vivo distribution in the rat. After dilution in neutral normal saline compound A is metastable and after a short half-life it is transformed into the other 99mTc-Sn-pyrophosphate compound A is metastable and after a short half-life in bone but in the kidneys. After dilution in normal saline of low pH and in buffering solutions the stability of compound A is increased. In human plasma compound A is relatively stable but not in plasma water. When compound B is formed in a buffering solution, uptake in the kidneys and excretion in urine is lowered and blood concentration increased.It is assumed that the association of protons to compound A will increase its stability at low concentrations while that to compound B will lead to a strong protein bond in plasma. It is concluded that compound A will not be stable in vivo because of a lack of stability in the extravascular space, and that the protein bond in plasma will be a measure of its in vivo stability.

Neutrophil Elastase Potentiates Cathepsin G-lnduced Platelet Activation

1992 ◽  
Vol 68 (05) ◽  
pp. 570-576 ◽  
Author(s):  
Mary A Selak
Keyword(s):  
Neutrophil Elastase ◽  
Cell Activation ◽  
Thromboxane A2 ◽  
Creatine Phosphate ◽  
Dense Granule ◽  
Cathepsin G ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Low Concentrations ◽  
High Concentrations

SummaryWe have previously demonstrated that human neutrophil cathepsin G is a strong platelet agonist that binds to a specific receptor. This work describes the effect of neutrophil elastase on cathepsin G-induced platelet responses. While platelets were not activated by high concentrations of neutrophil elastase by itself, elastase enhanced aggregation, secretion and calcium mobilization induced by low concentrations of cathepsin G. Platelet aggregation and secretion were potentiated in a concentration-dependent manner by neutrophil elastase with maximal responses observable at 200 nM. Enhancement was observed when elastase was preincubated with platelets for time intervals of 10–60 s prior to addition of a low concentration of cathepsin G and required catalytically-active elastase since phenylmethanesulphonyl fluoride-inhibited enzyme failed to potentiate cell activation. Neutrophil elastase potentiation of platelet responses induced by low concentrations of cathepsin G was markedly inhibited by creatine phosphate/creatine phosphokinase and/or indomethacin, indicating that the synergism between elastase and cathepsin G required the participation of ADP and thromboxane A2. On the other hand, platelet responses were not attenuated by the PAF antagonist BN 52021, signifying that PAF-acether did not play a role in elastase potentiation. At higher concentrations porcine pancreatic elastase exhibits similar effects to neutrophil elastase, demonstrating that the effect of elastase was not unique to the neutrophil protease. While neutrophil elastase failed to alter the ability of cathepsin G to hydrolyze a synthetic chromogenic substrate, preincubation of platelets with elastase increased the apparent affinity of cathepsin G binding to platelets. In contrast to their effect on cathepsin G-induced platelet responses, neither neutrophil nor pancreatic elasatse potentiated aggregation or dense granule release initiated by ADP, PAF-acether, arachidonic acid or U46619, a thromboxane A2 mimetic. Moreover, unlike its effect on cathepsin G, neutrophil elastase inhibited thrombin-induced responses. The current observations demonstrate that elastase can potentiate platelet responses mediated by low concentrations of cathepsin G, suggesting that both enzymes may function synergistically to activate platelets under conditions where neutrophil degranulation occurs.

In Vitro Effects of Ethanol on Rabbit Platelet Aggregation, Secretion of Granule Contents, and Cyclic AMP Levels in the Presence of Prostacyclin

1989 ◽  
Vol 61 (02) ◽  
pp. 254-258 ◽  
Author(s):  
Margaret L Rand ◽  
Peter L Gross ◽  
Donna M Jakowec ◽  
Marian A Packham ◽  
J Fraser Mustard
Keyword(s):  
Cyclic Amp ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Inhibitory Effects ◽  
Low Concentrations ◽  
Rabbit Platelets ◽  
High Concentrations ◽  
In Vitro Effects ◽  
Aggregation Of Platelets

SummaryEthanol, at physiologically tolerable concentrations, inhibits platelet responses to low concentrations of collagen or thrombin, but does not inhibit responses of washed rabbit platelets stimulated with high concentrations of ADP, collagen, or thrombin. However, when platelet responses to high concentrations of collagen or thrombin had been partially inhibited by prostacyclin (PGI2), ethanol had additional inhibitory effects on aggregation and secretion. These effects were also observed with aspirin- treated platelets stimulated with thrombin. Ethanol had no further inhibitory effect on aggregation of platelets stimulated with ADP, or the combination of ADP and epinephrine. Thus, the inhibitory effects of ethanol on platelet responses in the presence of PGI2 were very similar to its inhibitory effects in the absence of PGI2, when platelets were stimulated with lower concentrations of collagen or thrombin. Ethanol did not appear to exert its inhibitory effects by increasing cyclic AMP above basal levels and the additional inhibitory effects of ethanol in the presence of PGI2 did not appear to be brought about by further increases in platelet cyclic AMP levels.

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