scholarly journals Allosteric inhibition of methylenetetrahydrofolate reductase by adenosylmethionine. Effects of adenosylmethionine and NADPH on the equilibrium between active and inactive forms of the enzyme and on the kinetics of approach to equilibrium.

1987 ◽  
Vol 262 (6) ◽  
pp. 2485-2493 ◽  
Author(s):  
D.A. Jencks ◽  
R.G. Mathews
Keyword(s):  
Methylenetetrahydrofolate Reductase ◽  
Approach To Equilibrium ◽  
Allosteric Inhibition ◽  
Kinetics Of

Kinetics of Vascular and Extravascular Protein Exchange in Unbled and Bled Dogs

1955 ◽  
Vol 184 (1) ◽  
pp. 175-182 ◽  
Author(s):  
Karlman Wasserman ◽  
Jeanne D. Joseph ◽  
H. S. Mayerson
Keyword(s):  
Specific Activity ◽  
Blood Stream ◽  
Separate Entity ◽  
Approach To Equilibrium ◽  
Plasma Albumin ◽  
Compartment System ◽  
Specific Activities ◽  
Almost All ◽  
Kinetics Of ◽  
Extravascular Compartment

Unanesthetized, healthy greyhounds were infused with 25% albumin or bled, injected with I131-labeled albumin and albumin specific activities determined. It is shown that the albumin specific activity curves can be altered by changing the ratio of the vascular to extravascular albumin masses in a manner predicted from the mathematics of a two-compartment system. Increase of vascular albumin mass relative to extravascular mass results in a smaller initial disappearance of albumin specific activity from the blood stream and a faster approach to equilibrium. Decrease of vascular albumin mass relative to extravascular mass by bleeding shows that 50% of albumin replacement after hemorrhage appears to be accomplished within 24 hours. Almost all of this protein comes from the extravascular compartment. Rapid anabolism accounts for the replenishment of protein for the next 2–5 days, during and after which there is a reduced catabolism of the existing plasma albumin. The results indicate that an extravascular albumin mass exists as a separate entity and net movements may occur from this mass into the plasma when the equilibrium between the vascular and extravascular masses is disturbed.

scholarly journals Kinetics of Materials at Extreme Conditions: Understanding the Time Dependent Approach to Equilibrium at MaRIE

2017 ◽  
Author(s):  
R. G. Kraus ◽  
D. Mcnabb ◽  
M. Kumar ◽  
J. Eggert ◽  
J. Borg ◽  
...  
Keyword(s):  
Time Dependent ◽  
Extreme Conditions ◽  
Approach To Equilibrium ◽  
Kinetics Of

Kinetics of Allosteric Inhibition of Single Enzyme by Product Molecules

2020 ◽  
Vol 124 (52) ◽  
pp. 11793-11801
Author(s):  
Prasanta Kundu ◽  
Soma Saha ◽  
Gautam Gangopadhyay
Keyword(s):  
Allosteric Inhibition ◽  
Kinetics Of ◽  
Single Enzyme

Effect of acute hyperhomocysteinemia on methylation potential of erythrocytes and on DNA methylation of lymphocytes in healthy male volunteers

2005 ◽  
Vol 289 (4) ◽  
pp. F786-F792 ◽  
Author(s):  
R. Fux ◽  
D. Kloor ◽  
M. Hermes ◽  
T. Röck ◽  
B. Proksch ◽  
...  
Keyword(s):  
Dna Methylation ◽  
Methylenetetrahydrofolate Reductase ◽  
Global Dna Methylation ◽  
Methyl Groups ◽  
Healthy Male ◽  
Dna Hypomethylation ◽  
Plasma Thcy ◽  
Acute Elevation ◽  
Total Homocysteine ◽  
Kinetics Of

Homocysteine is a precursor of S-adenosylmethionine (AdoMet) and a metabolite of S-adenosylhomocysteine (AdoHcy). The ratio of AdoMet to AdoHcy, defined as the methylation potential (MP), indicates the flow of methyl groups within the cells. Chronic elevations of total homocysteine (tHcy) in plasma correlate with increased AdoHcy concentrations, decreased MP, and impaired DNA methylation. However, the influence of acute hyperhomocysteinemia on MP is unknown. We induced acute hyperhomocysteinemia in 14 healthy volunteers by oral administration of l-homocysteine (65.1 μmol/kg body wt) in an open, randomized, placebo-controlled two-period crossover study. The kinetics of tHcy in blood and urine, MP in blood, and global DNA methylation in lymphocytes were studied systematically during 48 h. Plasma tHcy concentrations reached a peak at 34 ± 11 min after an oral load with l-homocysteine and decreased with a half-life of 257 ± 41 min (means ± SD). Only 2.3% of the homocysteine dose were recovered in urine. AdoHcy concentrations and MP in whole blood and erythrocytes were not affected by the oral homocysteine load. Furthermore, global DNA methylation in lymphocytes did not change under these conditions. We found no difference between the genotypes of 5,10-methylenetetrahydrofolate reductase in response to the homocysteine load. However, AdoMet content in erythrocytes was significantly higher in the C677T carriers (CT; n = 7) compared with the CC genotype ( n = 7). Although chronic elevation of tHcy has been shown to affect MP and DNA methylation, acute elevation of plasma tHcy above 20 μmol/l for 8 h is not sufficient to change MP and to induce DNA hypomethylation in lymphocytes.

Kinetics of the approach to equilibrium shape of a disc-shaped precipitate

1977 ◽  
Vol 11 (8) ◽  
pp. 677-680 ◽  
Author(s):  
G.J. Shiflet ◽  
H.I. Aaronson ◽  
T.H. Courtney
Keyword(s):  
Equilibrium Shape ◽  
Approach To Equilibrium ◽  
Kinetics Of

On the kinetics of the approach to equilibrium

Physica ◽  
1961 ◽  
Vol 27 (7) ◽  
pp. 629-646 ◽  
Author(s):  
I. Prigonine ◽  
P. Résibois
Keyword(s):  
Approach To Equilibrium ◽  
Kinetics Of

scholarly journals THE KINETICS OF PENETRATION

1934 ◽  
Vol 17 (4) ◽  
pp. 507-516 ◽  
Author(s):  
W. J. V. Osterhout ◽  
S. E. Kamerling
Keyword(s):  
Aqueous Phase ◽  
Partition Coefficients ◽  
Organic Anion ◽  
External Solution ◽  
Living Cells ◽  
Approach To Equilibrium ◽  
Aqueous Layer ◽  
Pass Through ◽  
Kinetics Of ◽  
System Approaches

A model is described which throws light on the mechanism of accumulation. In the model used an external aqueous phase A is separated by a non-aqueous phase B (representing the protoplasm) from the artificial sap in C. A contains KOH and C contains HCl: they tend to mix by passing through the non-aqueous layer but much more KOH moves so that most of the KCl is formed in C, where the concentration of potassium becomes much greater than in A. This accumulation is only temporary for as the system approaches equilibrium the composition of A approaches identity with that of C, since all the substances present can pass through the non-aqueous layer. Such an approach to equilibrium may be compared to the death of the cell as the result of which accumulation disappears. During the earlier stages of the experiment potassium tends to go in as KOH and at the same time to go out as KCl. These opposing tendencies do not balance until the concentration of potassium inside becomes much greater than outside (hence potassium accumulates). The reason is that KCl, although its driving force be great, moves very slowly in B because its partition coefficient is low and in consequence its concentration gradient in B is small. This illustrates the importance of partition coefficients for penetration in models and in living cells. It also indicates that accumulation depends on the fact that permeability is greater for the ingoing compound of the accumulating substance than for the outgoing compound. Other things being equal, accumulation is increased by maintaining a low pH in C. Hence we may infer that anything which checks the production of acid in the living cell may be expected to check accumulation and growth. This model recalls the situation in Valonia and in most living cells where potassium accumulates as KCl, perhaps because it enters as KOH and forms KA in the sap (where A is an organic anion). In some plants potassium accumulates as KA but when HCl exists in the external solution it will tend to enter and displace the weaker acid HA (if this be carbonic it can readily escape): hence potassium may accumulate to a greater or less extent as KCl. Injury of the cell may produce a twofold effect, (1) increase of permeability, (2) lessened accumulation. The total amount of electrolyte taken up in a given time will be influenced by these factors and may be greater than normal in the injured cell or less, depending somewhat on the length of the interval of time chosen.

Direct observations of radiation-enhanced transformations in glass

1983 ◽  
Vol 41 ◽  
pp. 354-355
Author(s):  
J. F. DeNatale ◽  
D. G. Howitt
Keyword(s):  
Glass Matrix ◽  
Diffusion Mechanism ◽  
Bubble Formation ◽  
Silicate Glasses ◽  
Phase Decomposition ◽  
Direct Observations ◽  
Thin Foils ◽  
Oxygen Bubble ◽  
Electron Energy Loss ◽  
Kinetics Of

The electron irradiation of silicate glasses containing metal cations produces various types of phase separation and decomposition which includes oxygen bubble formation at intermediate temperatures figure I. The kinetics of bubble formation are too rapid to be accounted for by oxygen diffusion but the behavior is consistent with a cation diffusion mechanism if the amount of oxygen in the bubble is not significantly different from that in the same volume of silicate glass. The formation of oxygen bubbles is often accompanied by precipitation of crystalline phases and/or amorphous phase decomposition in the regions between the bubbles and the detection of differences in oxygen concentration between the bubble and matrix by electron energy loss spectroscopy cannot be discerned (figure 2) even when the bubble occupies the majority of the foil depth.The oxygen bubbles are stable, even in the thin foils, months after irradiation and if van der Waals behavior of the interior gas is assumed an oxygen pressure of about 4000 atmospheres must be sustained for a 100 bubble if the surface tension with the glass matrix is to balance against it at intermediate temperatures.

Irradiation behavior of pyrolytic silicon carbide

1983 ◽  
Vol 41 ◽  
pp. 72-73
Author(s):  
R. J. Lauf
Keyword(s):  
Silicon Carbide ◽  
Fission Products ◽  
Thermodynamics And Kinetics ◽  
Neutron Fluences ◽  
Fuel Particles ◽  
Sic Coatings ◽  
Irradiation Behavior ◽  
Kinetics Of ◽  
Htgr Fuel

Fuel particles for the High-Temperature Gas-Cooled Reactor (HTGR) contain a layer of pyrolytic silicon carbide to act as a miniature pressure vessel and primary fission product barrier. Optimization of the SiC with respect to fuel performance involves four areas of study: (a) characterization of as-deposited SiC coatings; (b) thermodynamics and kinetics of chemical reactions between SiC and fission products; (c) irradiation behavior of SiC in the absence of fission products; and (d) combined effects of irradiation and fission products. This paper reports the behavior of SiC deposited on inert microspheres and irradiated to fast neutron fluences typical of HTGR fuel at end-of-life.

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