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.

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 The Kinetics of Clearance from the Circulation of Man of Heparin and a Semi-Synthetic Heparin Analogue

1977 ◽  
Author(s):  
D. A. Lane ◽  
R. Michalski ◽  
V. V. Kakkar
Keyword(s):  
High Specificity ◽  
Antithrombotic Agent ◽  
First Order ◽  
First Order Kinetics ◽  
Zero Order Kinetics ◽  
Low Concentrations ◽  
Equal Dose ◽  
Rapid Clearance ◽  
The Difference ◽  
High Concentrations

A study has been made of a low molecular weight semi-synthetic heparin analogue, (SSHA) that may be clinically useful as an antithrombotic agent because of itsreported high specificity for potentiating antithrombin III activity. The clearance from the circulation of both heparin and the analogue has been studied in man following intravenous injection. Heparin obeyed almost zero order kinetics when assayed using a specific anti-Xa assay and first order kinetics when measured with KCCT. At high concentrations the heparin analogue was cleared with first order kinetics when assayed both with the anti-Xa assay and with KCCT. At low concentrations the analogue produced between one half and two-thirds of the anti-Xa activity of an equal dose of heparin, producing only a small prolongation of KCCT. With increasing dose, the more specific anti-Xa potentiating effect of SSHA decreased in part because of the difference in kinetic behaviour between heparin and SSHAbut largely because of a flattening of its anti-Xa dose response curve. Because of the initial more rapid clearance of higher doses of heparin from plasma when it is measured by the KCCT, these results suggest that the use of KCCT can cause a small underestimate of circulating heparin anti-thrombotic activity.

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.

scholarly journals Mechanisms of thermoinactivation of endoglucanase I from Trichoderma reesei QM 9414

1992 ◽  
Vol 287 (2) ◽  
pp. 583-588 ◽  
Author(s):  
J M Dominguez ◽  
C Acebal ◽  
J Jimenez ◽  
I de la Mata ◽  
R Macarron ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Trichoderma Reesei ◽  
Time Course ◽  
Enzyme Concentration ◽  
Main Process ◽  
Peptide Bonds ◽  
First Order ◽  
First Order Kinetics ◽  
Endoglucanase I ◽  
Hydrolysis Of

The mechanism of irreversible thermoinactivation of endoglucanase I from Trichoderma reesei has been determined at 70 degrees C at the pH of maximum enzyme activity. The time-course of thermoinactivation did not follow first-order kinetics and kinetic constants of the process were dependent on enzyme concentration, suggesting that aggregation was the main process leading to irreversible inactivation. The enzyme was extremely resistant to urea, which in fact seemed to stabilize it against temperature. Disulphide exchange, deamidation and hydrolysis of peptide bonds were also responsible for the loss of enzyme activity at 70 degrees C.

scholarly journals Involvement of superoxide anion in the reaction mechanism of haemoglobin oxidation by nitrite

1981 ◽  
Vol 193 (1) ◽  
pp. 169-179 ◽  
Author(s):  
A Tomoda ◽  
A Tsuji ◽  
Y Yoneyama
Keyword(s):  
Superoxide Anion ◽  
Time Course ◽  
Reaction Model ◽  
Slow Phase ◽  
British Library ◽  
Functional Difference ◽  
First Order ◽  
Slow Reaction ◽  
First Order Kinetics ◽  
Beta 2

The sigmoidal time course of haemoglobin oxidation by nitrite, involving an initial slow reaction accompanied by a subsequent rapid reaction, was extensively explored. The initial slow reaction was much prolonged by the addition of superoxide dismutase to the reaction mixture. On the other hand, in the presence of superoxide anion generated by xanthine oxidase systems, the slow phase disappeared and the reaction changed to first-order kinetics. The oxidation of intermediate haemoglobins [defined as haemoglobin tetramer in which different chains (alpha- or beta-) are in the ferric state and in the ferrous state] such as (alpha 2+ beta 3+)2 and (alpha 3+ beta 2+)2 also proceeded in a sigmoidal manner. Similar effects of superoxide anion on these reactions were observed. Since the intermediate haemoglobins such as (alpha 2+ beta 3+)2 and (alpha 3+ beta 2+)2 were found to be produced by the oxidation of haemoglobin by nitrite, the changes in oxyhaemoglobin, intermediate haemoglobins and methaemoglobin during the reaction were followed by isoelectric-focusing electrophoresis. The amounts of (alpha 2+ beta 3+)2 were larger than those of (alpha 3+ beta 2+)2 at the initial stages of the reaction, suggesting that there is a functional difference between alpha- and beta-chains in the oxyhaemoglobin tetramer. On the basis of these results, a reaction model of the haemoglobin oxidation by nitrite was tentatively proposed. The changes in oxyhaemoglobin, intermediate haemoglobins and methaemoglobin were well fitted to the simulation curves generated from the reaction model. Details of the derivation of the equations used for kinetic analysis have been deposited as Supplement SUP 50112 (5 pages) with the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K. from whom copies may be obtained on the terms indicated in Biochem. J. (1978) 169, 5.

Efficient degradation of tetracycline by ultraviolet-based activation of peroxymonosulfate and persulfate

2019 ◽  
Vol 79 (5) ◽  
pp. 911-920 ◽  
Author(s):  
Jiamin Hu ◽  
Jing Zhang ◽  
Qingguo Wang ◽  
Qian Ye ◽  
Hao Xu ◽  
...  
Keyword(s):  
Degradation Kinetics ◽  
Oxidative Capacity ◽  
Kinetics Model ◽  
Primary Radical ◽  
First Order ◽  
Uv Illumination ◽  
First Order Kinetics ◽  
Two Systems ◽  
Pseudo First Order ◽  
The Difference

Abstract In this study, the difference in oxidative capacity for removing antibiotics and the mechanism between the Cu(II)/peroxymonosulfate (PMS)/UV and Cu(II)/persulfate (PDS)/UV systems were compared under various conditions. The optimal Cu(II) concentration in the Cu(II)/PMS/UV system was 30 μM, and in the Cu(II)/PDS/UV system was 50 μM. With the PMS or PDS concentration increasing, higher tetracycline (TC) degradation in these two systems occurred. Investigation on the mechanism revealed that •OH was the primary radical in the Cu(II)/PMS/UV system, while SO4−• was the primary radical in the Cu(II)/PDS/UV system where •OH also played an important role. In these two systems, it was observed that Cu(I) was generated by PMS or PDS activated via UV illumination; however, oxygen alone could not promote TC removal. The degradation of TC was increased with the increasing pH level. In addition, TC degradation in the Cu(II)/PMS/UV system followed the pseudo-first-order kinetics model during the entire reaction period. It was found that the TC degradation kinetics in the Cu(II)/PDS/UV system can be divided into two parts (0 to 7 min and 10 to 50 min) and these two parts had good agreement with the pseudo-first-order kinetics model, respectively.

Re-examination of the kinetics of the thermal dehydroxylation of kaolinite

Clay Minerals ◽  
1984 ◽  
Vol 19 (4) ◽  
pp. 653-661 ◽  
Author(s):  
J. M. Criado ◽  
A. Ortega ◽  
C. Real ◽  
E. Torres De Torres
Keyword(s):  
Reaction Mechanism ◽  
Diffusion Process ◽  
Diffusion Mechanism ◽  
Activation Energies ◽  
First Order ◽  
First Order Kinetics ◽  
Comparison Of The Results ◽  
Kinetics Of

AbstractThe results obtained from this study of kaolinite dehydroxylation explain why different investigators have ascribed both first-order kinetics and a diffusion mechanism to this reaction. The fact that activation energies reported by these workers agree well, in spite of the different kinetics assumed when performing the calculations, is also explained. From a comparison of the results obtained by isothermal and non-isothermal methods it is concluded that, for reacted fractions,α, <0·6, kaolinite dehydroxylation is controlled by a diffusion process. A reaction mechanism explaining this behaviour is proposed.

Selective Binding Of [3H]Yohimbine To The α2-Receptor Of Intact Platelets -- Comparison With [3H] Dihydroergocryptine Binding

1981 ◽  
Author(s):  
Donald E Macfarlane ◽  
David C Stump
Keyword(s):  
Adenylate Cyclase ◽  
Time Course ◽  
Specific Binding ◽  
Receptor Occupancy ◽  
Scatchard Analysis ◽  
Binding Mechanism ◽  
Selective Binding ◽  
First Order ◽  
First Order Kinetics ◽  
Experimental Variation

Analysis of the coupling of receptors and the adenylate cyclase is facilitated by radioligand analysis of receptor occupancy. The platelet α-receptor has been characterized by [3H]dihydroergocryptine binding to membranes, but poorly reproducible results are obtained with intact platelets. We incubated washed platelets with [3H]dihydroergocryptine and measured bound counts after 6-fold dilution with plasma and centrifugation. After 10 minutes, phentolamine (5μM) suppressible counts equivalent to 400 molecules per platelet were found with 1/2 saturation at 1.2nM. There was considerable intra-experimental variation, and non-specific binding “space” was greater than 10μl/108 platelets. Time course of displacement with cold dihydroergocryptine, phentolamine or yohimbine was biphasic with a rapid (2 min) component amounting to 20-30% followed by a further 20% over the next 60 minutes. These results, which confirm those of others, suggest that equilibrium is not reached in a reasonable period of time and that more than one binding mechanism may be involved. In contrast, [3H]yohimbine bound with simple first order kinetics (37°) giving k1 = 5.25 × 105M-1 and k-1 = 3.33 × 10-3sec-1. Scatchard analysis revealed kd = 4.8 nM, Bmax = 180 molecules per platelet. Non-specific binding “space” was less than 1μl/108 platelets. Binding was completely reversed or prevented by epinephrine, clonidine, ρ-aminoclonidine, phentolamine, dihydroergotamine and dihydroergocryptine in that order of potency. Prazosin, an α1-antagonist, was less potent than epinephrine. Yohimbine blocks the ability of epinephrine to potentiate and induce aggregation, and to inhibit the adenylate cyclase. It is concluded that this novel radioligand has clear advantages over dihydroergocryptine for analysis of receptor occupancy in intact platelets.

Destruction of Actin Filaments by Osmium Tetroxide

1977 ◽  
Vol 35 ◽  
pp. 466-467
Author(s):  
P. Maupin-Szamier ◽  
T. D. Pollard
Keyword(s):  
Actin Filaments ◽  
Time Course ◽  
Osmium Tetroxide ◽  
Rabbit Muscle ◽  
Muscle Actin ◽  
Sodium Phosphate Buffer ◽  
Transmission Electron ◽  
The Difference ◽  
Rates Of Decay ◽  
Short Time

We have studied the destruction of rabbit muscle actin filaments by osmium tetroxide (OSO4) to develop methods which will preserve the structure of actin filaments during preparation for transmission electron microscopy.Negatively stained F-actin, which appears as smooth, gently curved filaments in control samples (Fig. 1a), acquire an angular, distorted profile and break into progressively shorter pieces after exposure to OSO4 (Fig. 1b,c). We followed the time course of the reaction with viscometry since it is a simple, quantitative method to assess filament integrity. The difference in rates of decay in viscosity of polymerized actin solutions after the addition of four concentrations of OSO4 is illustrated in Fig. 2. Viscometry indicated that the rate of actin filament destruction is also dependent upon temperature, buffer type, buffer concentration, and pH, and requires the continued presence of OSO4. The conditions most favorable to filament preservation are fixation in a low concentration of OSO4 for a short time at 0°C in 100mM sodium phosphate buffer, pH 6.0.

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