scholarly journals Cyclic 3', 5'-AMP relay in dictyostelium discoideum. IV. Recovery of the cAMP signaling response after adaptation to cAMP

1980 ◽  
Vol 86 (2) ◽  
pp. 545-553 ◽  
Author(s):  
M Dinauer ◽  
TL Steck ◽  
P Devreotes
Keyword(s):  
Time Course ◽  
Recovery Period ◽  
Camp Signaling ◽  
Intracellular Camp ◽  
Surface Receptors ◽  
First Order ◽  
Cellular Processes ◽  
First Order Kinetics ◽  
Rate Limiting Step ◽  
Rate Limiting

In dictyoselium discoideum, an increase in extracellular cAMP activates adenylate cyclase, leading to an increase in intracellular cAMP and the rate of cAMP secretion. Cells adapt to any constant cAMP stimulus after several minutes, but still respond to an increase in the concentration of the stimulus. We have now characterized the decay of adaptation (deadaptation) after the removal of cAMP stimuli. Levels of adaptation were established by the perfusion of [(3)H]adenosine-labeled amoebae with a defined cAMP stimulus. After a variable recovery period, the magnitude of the signaling response to a second stimulus was measured; its attenuation was taken as a measure of residual adaption to the first stimulus. The level of adaptation established by the first stimulus depended on both its magnitude and duration. Deadaptation began as soon as the first stimulus was removed. The magnitude of the response to the second stimulus increased with the recovery time in a first-order fashion, with a t(1/2)=3-4 min for stimuli of 10(-8) M to 10(-5) M cAMP. Responses to test stimuli, although reduced in magnitude, had an accelerated time-course when they closely followed a prior response that had not completely subsided. This effect is called priming; we believe it reveals a reversible, rate-limiting step that modulates the onset and termination of the signaling responses of amoebae that have not recently responded to a cAMP stimulus. We have suggested that the cAMP signaling response is controlled by two antagonistic cellular processes, excitation and adaptation. The data reported here imply that both the rate of rise in the adaptation process and the final level reached depend on the occupancy of cAMP surface receptors and that the decay of adaptation when external cAMP is removed proceeds with first-order kinetics.

Time course and vectorial nature of albumin metabolism in isolated perfused rabbit PCT

1988 ◽  
Vol 255 (3) ◽  
pp. F520-F528 ◽  
Author(s):  
C. H. Park
Keyword(s):  
Time Course ◽  
Hydrolysis Product ◽  
High Capacity ◽  
Intact Protein ◽  
Renal Metabolism ◽  
First Order ◽  
First Order Kinetics ◽  
Hydrolysis Products ◽  
Renal Tubular ◽  
Hydrolysis Of

The time course and vectorial nature of renal metabolism of albumin (Alb) were studied. The tubular absorption, accumulation, and hydrolysis of Alb and the release of the hydrolysis products were determined in the isolated rabbit proximal convoluted tubule (PCT) perfused with tritiated Alb ([3H3C]Alb) at 36.4 micrograms/ml. The Alb absorption across the apical membrane was constant (99.9 +/- 4.9 x 10(-3) ng.min-1.mm-1). In contrast, the accumulation and hydrolysis of Alb in the cells increased nonlinearly with time. The bulk of the tritium that accumulated in the cells was associated with intact [3H3C]Alb. Only the final hydrolysis products were released from the cells and these first appeared in the peritubular bath 6–7 min after the start of perfusion of the tubule with [3H3C]Alb. The hydrolysis product was not detectable in the tubule lumen. The proteolytic activity correlated linearly with the protein load to the cells, characteristic of first-order kinetics and a high-capacity system. The results suggest that the renal tubular handling of proteins proceeds from the apical to the basolateral aspect of the cell. The transcellular processing of Alb is rapid and can occur in 6–7 min. The accumulation of intact protein in the cell and the first-order kinetics of hydrolysis of the absorbed protein suggest that the rate-limiting step in proximal tubular handling of proteins may include the initial hydrolysis of protein or reside in steps that precede the hydrolysis.

scholarly journals Fusion accessibility of endocytic compartments along the recycling and lysosomal endocytic pathways in intact cells.

1989 ◽  
Vol 109 (5) ◽  
pp. 2097-2104 ◽  
Author(s):  
N H Salzman ◽  
F R Maxfield
Keyword(s):  
Time Course ◽  
Late Endosome ◽  
Intact Cells ◽  
Degradative Pathway ◽  
First Order ◽  
First Order Kinetics ◽  
Recycling Pathway ◽  
Endocytic Vesicles ◽  
Endocytic Compartments ◽  
Endocytic Pathways

A fluorescence assay developed for the quantitation of intracellular fusion of sequentially formed endocytic compartments (Salzman, N. H., and F. R. Maxfield. 1988 J. Cell Biol. 106:1083-1091) has been used to measure the time course of endosome fusion accessibility along the recycling and degradative endocytic pathways. Transferrin (Tf) was used to label the recycling pathway, and alpha2-macroglobulin (alpha 2 M) was used to label the lysosomal degradative pathway. Along the degradative pathway, accessibility of vesicles containing alpha 2M to fusion with subsequently formed endocytic vesicles decreased with apparent first order kinetics. The t12 for the loss of fusion accessibility was approximately 8 min. The behavior of Tf is more complex. Initially the fusion accessibility of Tf decayed rapidly (t1/2 less than 3 min), but a constant level of fusion accessibility was then observed for 10 min. This suggests that Tf moves through one fusion accessible endosome rapidly and then enters a second fusion accessible compartment on the recycling pathway. At 18 degrees C, fusion of antifluorescein antibodies (AFA) containing vesicles with F-alpha 2M was observed when the interval between additions was 10 min. However, if the interval was increased to 1 h, no fusion with incoming vesicles was observed. These results identify the site of F-alpha 2M accumulation at 18 degrees C as a prelysosomal late endosome that no longer fuses with newly formed endosomes since no delivery to lysosomes is observed at this temperature.

scholarly journals Small-molecule allosteric activators of PDE4 long form cyclic AMP phosphodiesterases

2019 ◽  
Vol 116 (27) ◽  
pp. 13320-13329 ◽  
Author(s):  
Faisa Omar ◽  
Jane E. Findlay ◽  
Gemma Carfray ◽  
Robert W. Allcock ◽  
Zhong Jiang ◽  
...  
Keyword(s):  
Cyclic Amp ◽  
Small Molecule ◽  
Protein Complexes ◽  
Cyst Formation ◽  
Camp Signaling ◽  
Intracellular Camp ◽  
Camp Phosphodiesterase ◽  
Cellular Processes ◽  
Small Molecule Compound ◽  
Autosomal Dominant Polycystic Kidney

Cyclic AMP (cAMP) phosphodiesterase-4 (PDE4) enzymes degrade cAMP and underpin the compartmentalization of cAMP signaling through their targeting to particular protein complexes and intracellular locales. We describe the discovery and characterization of a small-molecule compound that allosterically activates PDE4 long isoforms. This PDE4-specific activator displays reversible, noncompetitive kinetics of activation (increased Vmax with unchanged Km), phenocopies the ability of protein kinase A (PKA) to activate PDE4 long isoforms endogenously, and requires a dimeric enzyme assembly, as adopted by long, but not by short (monomeric), PDE4 isoforms. Abnormally elevated levels of cAMP provide a critical driver of the underpinning molecular pathology of autosomal dominant polycystic kidney disease (ADPKD) by promoting cyst formation that, ultimately, culminates in renal failure. Using both animal and human cell models of ADPKD, including ADPKD patient-derived primary cell cultures, we demonstrate that treatment with the prototypical PDE4 activator compound lowers intracellular cAMP levels, restrains cAMP-mediated signaling events, and profoundly inhibits cyst formation. PDE4 activator compounds thus have potential as therapeutics for treating disease driven by elevated cAMP signaling as well as providing a tool for evaluating the action of long PDE4 isoforms in regulating cAMP-mediated cellular processes.

Dibutyryl cAMP induces a gestation-dependent absorption of fetal lung liquid

1990 ◽  
Vol 68 (5) ◽  
pp. 2054-2059 ◽  
Author(s):  
D. V. Walters ◽  
C. A. Ramsden ◽  
R. E. Olver
Keyword(s):  
Fetal Lung ◽  
Liquid Volume ◽  
Intracellular Camp ◽  
Maximal Effect ◽  
Dibutyryl Camp ◽  
Rate Limiting Step ◽  
Liquid Absorption ◽  
Dependent Absorption ◽  
Lung Liquid ◽  
Rate Limiting

The maturation of the adenosine 3′,5′-cyclic monophosphate-(cAMP) dependent pathway controlling fetal lung liquid secretion was examined in experiments in which the lungs of chronically catheterized fetal lambs (123-141 days gestational age) were exposed to dibutyryl cAMP (DBcAMP, 10(-4) M). The effect of DBcAMP was markedly gestation dependent, with the greatest effect observed in the most mature fetuses. In immature fetuses (less than 130 days, mean age 125 days) DBcAMP caused slowing of secretion, with maximal effect at 5 h. With increasing maturity the effect of DBcAMP was more pronounced and occurred earlier so that in mature fetuses (mean age 140 days) lung liquid absorption took place, with maximal effect at 2 h. Changes in lung liquid volume flow induced by DBcAMP could be blocked by addition of 10(-4) M amiloride to lung liquid. It is concluded that 1) DBcAMP induces a change in lung liquid secretion that, like epinephrine, is mediated via an increase in Na+ permeability of the apical membrane of the lung epithelium and 2) the rate-limiting step in the maturation of this process must lie beyond the generation of intracellular cAMP.

Synthesis of the Water-Compatible P-Aminophenol Resin and its Adsorption for Salicylic Acid

2011 ◽  
Vol 311-313 ◽  
pp. 1852-1856 ◽  
Author(s):  
Gu Qing Xiao ◽  
Xue Jun Zhang
Keyword(s):  
Salicylic Acid ◽  
Adsorption Capacity ◽  
Equilibrium Concentration ◽  
Maximum Adsorption Capacity ◽  
Adsorption Dynamics ◽  
First Order ◽  
Rate Limiting Step ◽  
Intra Particle Diffusion ◽  
Rate Limiting ◽  
Order Rate Equation

A novel water-compatible hypercrosslinked resin modified by p-aminophenol was synthesized with chloromethylated polystyrene and p-aminophenol by Friedel-Crafts reaction. The objective of this work was to study the adsorption performances for salicylic acid onto p-aminophenol resin. The results showed that the adsorption capacity of salicylic acid onto p-aminophenol resin was superior to XAD-4 resin. It is seen that the maximum adsorption capacity is observed at pH of 3.0. It was found the adsorption dynamics obeyed the pseudo-first-order rate equation and the intra-particle diffusion was the rate-limiting step. The maximum adsorption capacity of salicylic acid for p-aminophenol resin was measured to be 283.7 mg/g with the equilibrium concentration at 404.6mg/L. The micropore structure, the pore diameter of p-aminophenol resin, the hydrogen bond between p-aminophenol resin and salicylic acid bring the larger adsorption capacity.

Oxidation of 1- and 2-acetylnaphthalenes by iodate - a kinetic study

1990 ◽  
Vol 55 (6) ◽  
pp. 1535-1540 ◽  
Author(s):  
Prerepa Manikyamba
Keyword(s):  
Solvent Effect ◽  
Enol Form ◽  
Aqueous Methanol ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Carbonium Ion ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of oxidation of 1- and 2-acetylnaphthalenes by iodate in the presence of sulphuric acid in aqueous methanol has been studied. The reaction is first order with respect to both [iodate] and [acetylnaphthalene]. Solvent effect indicates a cation-dipole type of interaction in the rate limiting step. A mechanism is proposed with a slow attack of IO2+ on enol form of acetylnaphthalene forming an intermediate carbonium ion, which ultimately gives corresponding ω-hydroxyacetylnaphthalene. The higher reactivity of 2-acetyl isomer is attributed to the greater stability of the corresponding carbonium ion than that of 1-acetyl isomer.

Physical Modeling of Backside Gettering

1984 ◽  
Vol 36 ◽  
Author(s):  
Gary B. Bronner ◽  
James D. Plummer
Keyword(s):  
Experimental Data ◽  
Physical Modeling ◽  
Equilibrium Concentration ◽  
Order Model ◽  
Phosphorus Diffusion ◽  
First Order ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Buried Layer ◽  
Rate Limiting

ABSTRACTTo understand gettering action we have modeled the diffusion of metal to a backside getter. A first order model describing the diffusion of metals to an infinite backside sink is found not to fit experimental data. To fit the data for phosphorus gettering at 1000°C and argon implantation gettering at 800°C it is necessary to also hypothesize the injection of silicon interstitials. Assuming that the diffusion of the silicon interstitials is the rate limiting step in gettering, allows one to extract the diffusion coefficient and equilibrium concentration of the interstitial. The hypothesis of silicon interstitial injection agrees with recent work on phosphorus diffusion by Fahey et. al. To test this hypothesis for heavily damaged regions we have looked at the effect of an argon implanted region on the diffusion of a phosphorus buried layer. At both 800°C and 700°C, during nitrogen anneals we see significant enhancement of the phosphorus diffusion.

URINARY EXCRETION OF INTRAVENOUSLY INJECTED 35S-SULPHATE AND 14C-UREA IN SHEEP

1975 ◽  
Vol 55 (2) ◽  
pp. 207-212 ◽  
Author(s):  
J. D. OLDHAM ◽  
G. W. MATHISON ◽  
L. P. MILLIGAN
Keyword(s):  
Urinary Excretion ◽  
Time Course ◽  
Microbial Growth ◽  
Diffusion Mechanism ◽  
Physiological Saline ◽  
Simple Diffusion ◽  
First Order ◽  
First Order Kinetics ◽  
The Difference

Sheep were injected intravenously with either 14C-urea (76.3–86.3 μc) orNa235SO4 (72.5–120.0 μc) in physiological saline. Total urinary excretion of label and, in one trial, the disappearance of label from plasma were measured for up to 106 h. Urinary recoveries were 64.9 ± 9.7% of injected 14C and 66.9 ± 12.7% of injected 35S. 35S was recovered more slowly than 14C; 99% of recovered label was collected in 36 ± 9 h after injection for 14C and in 84 ± 12 h for 35S. Disappearance of 14C from plasma approximated first-order kinetics but this was not true for 35S, which was apparently not excreted by a simple diffusion mechanism. The time course of 35S excretion from blood and into urine is discussed with reference to the potential of using the difference between intraruminally infused 35S and urinary 35S excretion as a measure of rumen microbial retention of 35S, and hence of microbial growth. It is concluded that large errors could be introduced into measurements of microbial growth by this method if that part of 35S that enters blood, but is not excreted into urine, is recycled within the animal to sites other than the rumen and retained therein.

Kinetics of Pb(IV) Oxidation of Substituted Methyl Mandelates — A L.F. E. R. Study

1986 ◽  
Vol 41 (4) ◽  
pp. 467-472
Author(s):  
Sudheer K. Banerjee ◽  
R. Shanker ◽  
Om P. Sachdeva
Keyword(s):  
Bond Rupture ◽  
Linear Free Energy Relationship ◽  
First Order ◽  
Keto Esters ◽  
Linear Free Energy ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Catalysed Reaction ◽  
Reaction Constant ◽  
Rate Limiting

Lead tetra acetate (Pb(IV) or LTA) oxidation of the esters X -C6H4-CH(OH)-COOCH3(X = H, m-NO2, p-NO2, m-Cl, p-Cl, p-Br. p-CH3 and p-C2H5) gives corresponding keto esters. The reaction is first order in [Pb(IV)] and second order in [Ester], and is catalysed by pyridine and 2,6-lutidine. The pyridine catalysed reaction is first order each in [Pb(IV)]. [Ester] and [Pyridine]. A kinetic isotope effect is observed in oxidation of methyl m andelate for both uncatalysed reaction (kH/kD = 4.2) and pyridine catalysed reaction (kH/kD = 1.8). Activation param eters for both uncatalysed and pyridine catalysed reactions are evaluated. The results are in accord with Linear Free Energy Relationship (L.F.E.R.) and the reaction constant (ϱ = +0.75) obtained supports proton transfer in the ɑ-C-H bond rupture in the rate limiting step. The role pf pyridine in catalysis, as a ligand or as a base is discussed

scholarly journals The carboxybiotin complex of pyruvate carboxylase. A kinetic analysis of the effects of Mg2+ ions on its stability and on its reaction with pyruvate

1984 ◽  
Vol 219 (1) ◽  
pp. 243-251 ◽  
Author(s):  
P V Attwood ◽  
J C Wallace ◽  
D B Keech
Keyword(s):  
Pyruvate Carboxylase ◽  
General Scheme ◽  
Order Rate Constant ◽  
Enzymic Activity ◽  
Slow Phase ◽  
First Order ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Pseudo First Order ◽  
Rate Limiting

The enzyme-[14C] carboxybiotin complex of sheep liver pyruvate carboxylase was isolated and the reaction between this and pyruvate was studied by using the quenched-flow rapid-reaction technique. At 0.5 degrees C the reaction was 80% complete within 180 ms. The reaction was monophasic and obeyed pseudo-first-order kinetics. Increasing concentrations of Mg2+ caused a decrease in the magnitude of the observed pseudo-first-order rate constant. Throughout the carboxylation of pyruvate, the rate-limiting step of the reaction occurred after the dissociation of carboxybiotin from the first sub-site, whereas in the slow phase of the reaction with 2-oxobutyrate this dissociation is the rate-limiting step. It is possible, from the reaction scheme proposed, that the inhibition of overall enzymic activity by high concentrations of Mg2+ could be caused by the transfer of the carboxy group from biotin to pyruvate becoming rate-limiting. The efficacy of a substrate as a signal for the movement of carboxybiotin from the first sub-site is reflected by the amount that the effective affinity of the enzyme- carboxybiotin complex for Mg2+ is lowered. In the presence of the substrates tested, the affinities of the carboxybiotin complex can be arranged in order of increasing magnitude, i.e.: (formula; see text). The kinetics of the decay of the enzyme-[14C] carboxybiotin complex at 0 degree C in the absence of substrates are similar to the reaction with pyruvate except that the carboxybiotin is also unstable in the first sub-site, to some degree. This similarity allows for the proposal of a general scheme for the decarboxylation of the enzyme- carboxybiotin complex in the presence or in the absence of substrates.

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