Transport of fluorescein in trichomes of Lycopersicon esculentum

1982 ◽  
Vol 60 (4) ◽  
pp. 397-402 ◽  
Author(s):  
Gregor F. Barclay ◽  
Carol A. Peterson ◽  
Melvin T. Tyree
Keyword(s):  
Lycopersicon Esculentum ◽  
Cytoplasmic Streaming ◽  
Cytochalasin B ◽  
The Other ◽  
Square Root ◽  
Inhibiting Effect ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Other Hand ◽  
Rate Limiting

Translocation of the dye disodium fluorescein (uranin) in trichomes of Lycopersicon esculentum (tomato) was nonpolar and proportional to the square root of time. Inhibition of cytoplasmic streaming by cytochalasin B had no effect on the rate of dye movement. On the other hand, disruption of plasmodesmatal connections between adjacent cells by plasmolysis strongly diminished the rate of fluorescein translocation. Subsequent deplasmolysis of the cells did not remove the inhibiting effect of plasmolysis. The data are consistent with the interpretation that dye movement proceeds by diffusion, the rate-limiting step being transport through plasmodesmatal connections.

Distribution of ornithine decarboxylase in ovaries of rat and hamster during pro-oestrus

1986 ◽  
Vol 113 (3) ◽  
pp. 403-409 ◽  
Author(s):  
Lo Persson ◽  
Karin Isaksson ◽  
Elsa Rosengren ◽  
Frank Sundler
Keyword(s):  
Ornithine Decarboxylase ◽  
Granulosa Cells ◽  
Physiological Function ◽  
The Other ◽  
Interstitial Tissue ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Other Hand ◽  
Rat Ovary ◽  
Rate Limiting

Abstract. The biosynthesis of polyamines is dramatically increased in the ovaries of rat and hamster during the evening of pro-oestrus. In an attempt to shed some light on the physiological function of this biosynthesis ornithine decarboxylase (ODC), which catalyzes the rate-limiting step in the biosynthesis of the polyamines, was immunohistochemically localized in the ovaries from rat and hamster during pro-oestrus. At dioestrus, only a few immunoreactive cells were found in the ovaries. During the evening of pro-oestrus, on the other hand, numerous immunoreactive cells were observed in the ovaries. These cells were confined to the internal thecal layer of Graafian as well as smaller follicles and to the interstitial tissue of the ovary. The granulosa cells appeared to be devoid of immunoreactive ODC. The hamster ovary, which during this time exhibited considerably higher levels of ODC activity than the ovaries from the rat, did accordingly contain more immunoreactive cells than the rat ovary.

scholarly journals Using pH dependence for understanding mechanisms in electrochemical CO reduction

2021 ◽  
Author(s):  
Georg Kastlunger ◽  
Lei Wang ◽  
Nitish Govindarajan ◽  
Hendrik H. Heenen ◽  
Stefan Ringe ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Ph Dependence ◽  
The Other ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Other Hand ◽  
Alkaline Conditions ◽  
Co Reduction ◽  
Rate Limiting ◽  
Electrolyte Ph

Utilizing electrochemical conversion of CO(2) into hydrocarbons and oxygenates is envisioned as a promising path towards closing the carbon cycle in modern technology. To this day, however, the exact reaction mechanisms towards the plethora of single and multi-carbon products on Cu electrodes are still disputed. This uncertainty even extends to the rate-limiting step of the respective reactions. Since multi-carbon products do not show a dependence on the electrolyte pH in neutral and alkaline media, CO dimerization on the Cu surface has been proposed as the rate-limiting step. However, other elementary steps would lead to the same pH dependence, namely the proton-electron transfer to *CO followed by subsequent coupling or the protonation of the *OCCO dimer. The pH dependence of methane production on the other hand suggests that the rate limiting step is located beyond the first proton-electron transfer to *CO. In order to conclusively identify the rate limiting steps in CO reduction, we analyzed the mechanisms on the basis of constant potential DFT calculations, CO reduction experiments on Cu at varying pH values (3 - 13) and fundamental rate theory. We find that, even in acidic media, the reaction rate towards multi-carbon products is nearly unchanged on an SHE potential scale, which indicates that its rate limiting step does not involve a proton donor. Hence, we deduce that the rate limiting step can indeed only consist of the coupling of two CO molecules on the surface, both in acidic and alkaline conditions. For methane, on the other hand, the rate-limiting step changes with the electrolyte pH from the first protonation step in acidic/neutral conditions to a later step in alkaline conditions. Finally, based on an in-depth kinetic analysis, we conclude that the pathway towards CH4 involving a surface combination of *CO and *H is unlikely, since it is unable to reproduce the measured current densities and Tafel slopes.

scholarly journals Importance of catalase in the disposal of hydrogen peroxide within human erythrocytes

Blood ◽  
1994 ◽  
Vol 84 (1) ◽  
pp. 325-330 ◽  
Author(s):  
GF Gaetani ◽  
HN Kirkman ◽  
R Mangerini ◽  
AM Ferraris
Keyword(s):  
Glutathione Peroxidase ◽  
Human Erythrocytes ◽  
The Other ◽  
Unexpected Result ◽  
System Function ◽  
Sequential Action ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Genetic Deficiency ◽  
Rate Limiting

The catalase within normal, intact human erythrocytes was completely inactivated with amino triazole. The rate of 14CO2 evolution, when the cells were subsequently incubated with 14C-labeled glucose, provided a measure of the rate at which NADPH was being oxidized by the glutathione peroxidase/reductase system for the disposal of H2O2. This rate was determined in control cells and in catalase-inactivated cells while the cells were exposed to H2O2, which was generated at various constant and predetermined rates by glucose oxidase. The results indicated that catalase handles approximately half of the generated H2O2. The glutathione peroxidase/reductase mechanism accounted for the other half. These results are in agreement with our earlier findings on erythrocytes of a subject with a genetic deficiency of catalase. However, an unexpected result with the present approach was the finding that the increased dependence on the glutathione peroxidase/reductase mechanism did not occur until greater than 98% of the catalase had been inactivated. The latter observation indicates that catalase and the glutathione peroxidase/reductase system function intracellularly in a manner very different from that previously ascribed to them. An explanation of the findings requires that the two methods of H2O2 disposal function in a coordinated way, such as a sequential action in which the glutathione peroxidase/reductase system is the rate-limiting step.

scholarly journals Use of a genetic variant to study the hexose transport properties of human skin fibroblasts

1990 ◽  
Vol 265 (3) ◽  
pp. 823-829 ◽  
Author(s):  
O T Mesmer ◽  
B A Gordon ◽  
C A Rupar ◽  
T C Y Lo
Keyword(s):  
Human Skin ◽  
Transport System ◽  
Cytochalasin B ◽  
Transport Systems ◽  
Hexose Transport ◽  
Glucose Starvation ◽  
Human Skin Fibroblasts ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Human skin fibroblasts from ‘normal’ subjects were found to possess at least two hexose transport systems. One system was responsible for the uptake of 2-deoxy-D-glucose (dGlc), D-glucose and D-galactose, whereas the other was responsible primarily for the uptake of 3-O-methyl-D-glucose (MeGlc). The transport of dGlc was the rate-limiting step in the uptake process; over 97% of the internalized dGlc was phosphorylated and the specific activity of hexokinase was several times higher than that for dGlc transport. The dGlc transport system was activated by glucose starvation, and was very sensitive to inhibition by cytochalasin B and energy uncouplers. Fibroblasts isolated from a patient with symptoms of hypoglycaemia were found to differ from their normal counterparts in the dGlc transport system. They exhibited a much higher transport affinity for dGlc, D-glucose and D-galactose, with no change in the respective transport capacity. Transport was not the rate-limiting step in dGlc uptake by these cells. Moreover, the patient's dGlc transport system was no longer sensitive to inhibition by cytochalasin B and energy uncouplers. This suggested that the intrinsic properties of the patient's dGlc transport system were altered. It should be noted that the patient's dGlc transport system could still be activated by glucose starvation. Despite the changes in the dGlc transport system, the MeGlc transport system in the patient's fibroblasts remained unaltered. The observed difference in the properties of the two hexose transport systems in the ‘normal’ and the patient's fibroblasts strongly suggests that the two transport systems may be coded or regulated by different genes. The present finding provides the first genetic evidence from naturally occurring fibroblasts indicating the presence of two different hexose transport systems.

Propargylic and Chromene Terminated Prepolymers. 3. Study of Homopolymerization and the Effect of the Chromene Content on Reaction Kinetics

1996 ◽  
Vol 8 (3) ◽  
pp. 341-361 ◽  
Author(s):  
M F Grenier-Loustalot ◽  
C Sanglar
Keyword(s):  
Reaction Kinetics ◽  
Rate Constant ◽  
Reaction Temperature ◽  
Considerable Effect ◽  
The Other ◽  
Thermally Induced ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Physicochemical Data ◽  
Rate Limiting

We have chemically synthesized CTR (chromene terminated resin) prepolymers in order to more specifically study the homopolymerization reaction of chromene. Physicochemical data were used to show the value of working with dichromene prepolymers instead of propargylic monomers. In particular, the homopolymerization reaction is less exothermic than the thermally induced ring formation. So, when the homopolymerization reaction is predominant, the processability of the final thermoset material will be easier. Besides, the rate constant of the homopolymerization reaction is higher than that measured for dipropargylic monomers. This explains the interest in overcoming β stage formation which is the kinetically rate limiting step. On the other end, the presence of residual propargylic functions in dichromene prepolymers after synthesis has no considerable effect on reaction temperature or advancement of reaction.

scholarly journals A novel hybrid SEIQR model incorporating the effect of quarantine and lockdown regulations for COVID-19

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
R. Prabakaran ◽  
Sherlyn Jemimah ◽  
Puneet Rawat ◽  
Divya Sharma ◽  
M. Michael Gromiha
Keyword(s):  
Mathematical Models ◽  
Qualitative Agreement ◽  
Mortality Rates ◽  
The Other ◽  
Disease Dynamics ◽  
Disease Propagation ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Geographical Regions ◽  
Rate Limiting

AbstractMitigating the devastating effect of COVID-19 is necessary to control the infectivity and mortality rates. Hence, several strategies such as quarantine of exposed and infected individuals and restricting movement through lockdown of geographical regions have been implemented in most countries. On the other hand, standard SEIR based mathematical models have been developed to understand the disease dynamics of COVID-19, and the proper inclusion of these restrictions is the rate-limiting step for the success of these models. In this work, we have developed a hybrid Susceptible-Exposed-Infected-Quarantined-Removed (SEIQR) model to explore the influence of quarantine and lockdown on disease propagation dynamics. The model is multi-compartmental, and it considers everyday variations in lockdown regulations, testing rate and quarantine individuals. Our model predicts a considerable difference in reported and actual recovered and deceased cases in qualitative agreement with recent reports.

scholarly journals Monosaccharide transport into lactating-rat mammary acini

1982 ◽  
Vol 204 (2) ◽  
pp. 493-501 ◽  
Author(s):  
L C Threadgold ◽  
H G Coore ◽  
N J Kuhn
Keyword(s):  
Plasma Membrane ◽  
Cytochalasin B ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Monosaccharide Transport ◽  
Rat Mammary Gland ◽  
The Mean ◽  
Rate Limiting ◽  
Rate Of Consumption ◽  
Uptake And Release

The uptake and release of 3-O-methyl-D-[3H]glucose at 37 degrees C by acini, prepared from lactating-rat mammary gland with collagenase, was inhibited by glucose, phloretin, cytochalasin B, HgCl2 and low temperature. Uptake and phosphorylation of 2-deoxy-D-[3H]glucose, studied in greater detail, could be ascribed to a specific, saturable, inhibitable, process of apparent Km 16 mM and Vmax. approx. 56 nmol/min per mg of protein, plus a non-specific, non-inhibitable process that was monitored with [14C]fructose. The mean rate of uptake of 5 mM-2-deoxyglucose (16 nmol/min per mg of protein) was similar to the rate of consumption of 5 mM-glucose, suggesting that transport was a rate-limiting step in the overall metabolism of glucose. This accords with evidence for a glucose gradient across the plasma membrane.

scholarly journals Importance of catalase in the disposal of hydrogen peroxide within human erythrocytes

Blood ◽  
1994 ◽  
Vol 84 (1) ◽  
pp. 325-330 ◽  
Author(s):  
GF Gaetani ◽  
HN Kirkman ◽  
R Mangerini ◽  
AM Ferraris
Keyword(s):  
Glutathione Peroxidase ◽  
Human Erythrocytes ◽  
The Other ◽  
Unexpected Result ◽  
System Function ◽  
Sequential Action ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Genetic Deficiency ◽  
Rate Limiting

Abstract The catalase within normal, intact human erythrocytes was completely inactivated with amino triazole. The rate of 14CO2 evolution, when the cells were subsequently incubated with 14C-labeled glucose, provided a measure of the rate at which NADPH was being oxidized by the glutathione peroxidase/reductase system for the disposal of H2O2. This rate was determined in control cells and in catalase-inactivated cells while the cells were exposed to H2O2, which was generated at various constant and predetermined rates by glucose oxidase. The results indicated that catalase handles approximately half of the generated H2O2. The glutathione peroxidase/reductase mechanism accounted for the other half. These results are in agreement with our earlier findings on erythrocytes of a subject with a genetic deficiency of catalase. However, an unexpected result with the present approach was the finding that the increased dependence on the glutathione peroxidase/reductase mechanism did not occur until greater than 98% of the catalase had been inactivated. The latter observation indicates that catalase and the glutathione peroxidase/reductase system function intracellularly in a manner very different from that previously ascribed to them. An explanation of the findings requires that the two methods of H2O2 disposal function in a coordinated way, such as a sequential action in which the glutathione peroxidase/reductase system is the rate-limiting step.

scholarly journals Identification of a Human Decapping Complex Associated with hUpf Proteins in Nonsense-Mediated Decay

2002 ◽  
Vol 22 (23) ◽  
pp. 8114-8121 ◽  
Author(s):  
Jens Lykke-Andersen
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Premature Termination ◽  
The Other ◽  
Nonsense Mediated Decay ◽  
Cell Extracts ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Premature Termination Codons ◽  
Rate Limiting ◽  
Decapping Enzymes

ABSTRACT Decapping is a key step in general and regulated mRNA decay. In Saccharomyces cerevisiae it constitutes a rate-limiting step in the nonsense-mediated decay pathway that rids cells of mRNAs containing premature termination codons. Here two human decapping enzymes are identified, hDcp1a and hDcp2, as well as a homolog of hDcp1a, termed hDcp1b. Transiently expressed hDcp1a and hDcp2 proteins localize primarily to the cytoplasm and form a complex in human cell extracts. hDcp1a and hDcp2 copurify with decapping activity, an activity sensitive to mutation of critical hDcp residues. Importantly, coimmunoprecipitation assays demonstrate that hDcp1a and hDcp2 interact with the nonsense-mediated decay factor hUpf1, both in the presence and in the absence of the other hUpf proteins, hUpf2, hUpf3a, and hUpf3b. These data suggest that a human decapping complex may be recruited to mRNAs containing premature termination codons by the hUpf proteins.

Sign in / Sign up

Export Citation Format

Share Document