The kinetics of neutrophil activation. The response to chemotactic peptides depends upon whether ligand-receptor interaction is rate-limiting.

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Download Full-text

Kinetics and mechanism of cyclization of N-(2-methoxycarbonylphenyl)-N’-methylsulphonamide to 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19911701 ◽

1991 ◽

Vol 56 (8) ◽

pp. 1701-1710 ◽

Cited By ~ 4

Author(s):

Jaromír Kaválek ◽

Vladimír Macháček ◽

Miloš Sedlák ◽

Vojeslav Štěrba

Keyword(s):

Potassium Hydroxide ◽

Acid Catalysis ◽

Potassium Hydroxide Solution ◽

Hydroxide Solution ◽

General Base ◽

Rate Limiting Step ◽

Limiting Step ◽

Cyclization Kinetics ◽

Rate Limiting ◽

Kinetics Of

The cyclization kinetics of N-(2-methylcarbonylphenyl)-N’-methylsulfonamide (IIb) into 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (Ib) has been studied in ethanolamine, morpholine, and butylamine buffers and in potassium hydroxide solution. The cyclization is subject to general base and general acid catalysis. The value of the Bronsted coefficient β is about 0.1, which indicates that splitting off of the proton from negatively charged tetrahedral intermediate represents the rate-limiting and thermodynamically favourable step. In the solutions of potassium hydroxide the cyclization of dianion of the starting ester IIb probably becomes the rate-limiting step.

Download Full-text

Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport

AJP Cell Physiology ◽

10.1152/ajpcell.1985.248.5.c498 ◽

1985 ◽

Vol 248 (5) ◽

pp. C498-C509 ◽

Cited By ~ 23

Author(s):

D. Restrepo ◽

G. A. Kimmich

Keyword(s):

Experimental Data ◽

Steady State ◽

Sugar Transport ◽

Enzyme Kinetic ◽

Steady State Distribution ◽

State Distribution ◽

Least Squares Fit ◽

Coupling Stoichiometry ◽

Rate Limiting ◽

Kinetics Of

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.

Download Full-text

Comment on “Precipitation kinetics of calcite in the system CaCO3-H2O-CO2: the conversion to CO2 by the slow process H+ + HCO3− → CO2 + H2O as a rate limiting step” by W. Dreybrodt, L. Eisenlohr, B. Madry, and S. Ringer

Geochimica et Cosmochimica Acta ◽

10.1016/s0016-7037(98)00257-9 ◽

1998 ◽

Vol 62 (23-24) ◽

pp. 3789-3790 ◽

Cited By ~ 9

Author(s):

Yuping Zhang ◽

Carlos A Grattoni

Keyword(s):

Precipitation Kinetics ◽

Slow Process ◽

Rate Limiting Step ◽

Limiting Step ◽

Rate Limiting ◽

Kinetics Of

Download Full-text

High field 1H NMR Studies of Sol-Gel Kinetics

MRS Proceedings ◽

10.1557/proc-73-157 ◽

1986 ◽

Vol 73 ◽

Cited By ~ 7

Author(s):

Bruce D. Kay ◽

Roger A. Assink

Keyword(s):

Equilibrium Distribution ◽

Sol Gel ◽

Nmr Studies ◽

H Nmr ◽

Rate Limiting Step ◽

Rate Of Hydrolysis ◽

Acid Catalyzed ◽

Product Species ◽

Rate Limiting ◽

Kinetics Of

ABSTRACTHigh resolution 1H NMR spectroscopy at high magnetic fields is employed to study the reaction kinetics of the Si(OCH3)4:CH3OH:H2O sol-gel system. Both the overall extent of reaction as a function of time and the equilibrium distribution of species are measured. In acid catalyzed solution, condensation is the rate limiting step while in base catalyzed solution, hydrolysis becomes rate limiting. A kinetic model in which the rate of hydrolysis is assumed to be independent of the adjacent functional groups is presented. This model correctly predicts the distribution of product species during the initial stages of the sol-gel reaction.

Download Full-text

Exploitation of the IDO Pathway in the Therapy of Rheumatoid Arthritis

International Journal of Tryptophan Research ◽

10.4137/ijtr.s11737 ◽

2013 ◽

Vol 6s1 ◽

pp. IJTR.S11737 ◽

Cited By ~ 5

Author(s):

Richard O. Williams

Keyword(s):

Rheumatoid Arthritis ◽

Anthranilic Acid ◽

Kynurenine Pathway ◽

Gene Encoding ◽

Rate Limiting Step ◽

Tryptophan Metabolites ◽

Synthetic Derivative ◽

Rate Limiting ◽

Kinetics Of ◽

Draining Lymph Nodes

Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting step along the kynurenine pathway and is thought to play a key role in immune homeostasis through depletion of tryptophan and accumulation of kynurenines. In this review we summarize recent research into the possibility of harnessing the IDO pathway for the therapy of rheumatoid arthritis. Inhibition of IDO activity, or knockout of the gene encoding IDO, was shown to cause an increase in the severity of collagen-induced arthritis, an animal model of rheumatoid arthritis. The increased severity of disease was associated with elevated numbers of pathogenic Th1 and Th17 cells in the joints and draining lymph nodes. In another study, analysis of the kinetics of expression of downstream kynurenine pathway enzymes during the course of arthritis revealed a potential role for tryptophan metabolites in resolution of arthritis. Furthermore, the therapeutic administration of L-kynurenine or [3,4-dimethoxycinnamonyl]-anthranilic acid (a synthetic derivative of 3-hydroxy-anthranilic acid) significantly reduced both clinical and histological progression of experimental arthritis. These findings raise the possibility of exploiting the IDO pathway for the therapy of autoimmune disease.

Download Full-text

Precipitation kinetics of calcite in the system CaCO3H2OC02: The conversion to CO2 by the slow process H++HCO3− → CO2+H2O as a rate limiting step

Geochimica et Cosmochimica Acta ◽

10.1016/s0016-7037(97)00201-9 ◽

1997 ◽

Vol 61 (18) ◽

pp. 3897-3904 ◽

Cited By ~ 91

Author(s):

W. Dreybrodt ◽

L. Eisenlohr ◽

B. Madry ◽

S. Ringer

Keyword(s):

Precipitation Kinetics ◽

Slow Process ◽

Rate Limiting Step ◽

Limiting Step ◽

Rate Limiting ◽

Kinetics Of

Download Full-text

Structure–Function Relations of the First and Fourth Predicted Extracellular Linkers of the Type IIa Na+/Pi Cotransporter

The Journal of General Physiology ◽

10.1085/jgp.200409060 ◽

2004 ◽

Vol 124 (5) ◽

pp. 475-488 ◽

Cited By ~ 18

Author(s):

Colin Ehnes ◽

Ian C. Forster ◽

Katja Kohler ◽

Andrea Bacconi ◽

Gerti Stange ◽

...

Keyword(s):

Conformational Changes ◽

Reaction Rates ◽

Transport Pathway ◽

Extracellular Medium ◽

Voltage Range ◽

Substituted Cysteine Accessibility ◽

Voltage Dependent ◽

Opposite Behavior ◽

Rate Limiting ◽

Kinetics Of

The putative first intracellular and third extracellular linkers are known to play important roles in defining the transport properties of the type IIa Na+-coupled phosphate cotransporter (Kohler, K., I.C. Forster, G. Stange, J. Biber, and H. Murer. 2002b. J. Gen. Physiol. 120:693–705). To investigate whether other stretches that link predicted transmembrane domains are also involved, the substituted cysteine accessibility method (SCAM) was applied to sites in the predicted first and fourth extracellular linkers (ECL-1 and ECL-4). Mutants based on the wild-type (WT) backbone, with substituted novel cysteines, were expressed in Xenopus oocytes, and their function was assayed by isotope uptake and electrophysiology. Functionally important sites were identified in both linkers by exposing cells to membrane permeant and impermeant methanethiosulfonate (MTS) reagents. The cysteine modification reaction rates for sites in ECL-1 were faster than those in ECL-4, which suggested that the latter were less accessible from the extracellular medium. Generally, a finite cotransport activity remained at the end of the modification reaction. The change in activity was due to altered voltage-dependent kinetics of the Pi-dependent current. For example, cys substitution at Gly-134 in ECL-1 resulted in rate-limiting, voltage-independent cotransport activity for V ≤ −80 mV, whereas the WT exhibited a linear voltage dependency. After cys modification, this mutant displayed a supralinear voltage dependency in the same voltage range. The opposite behavior was documented for cys substitution at Met-533 in ECL-4. Modification of cysteines at two other sites in ECL-1 (Ile-136 and Phe-137) also resulted in supralinear voltage dependencies for hyperpolarizing potentials. Taken together, these findings suggest that ECL-1 and ECL-4 may not directly form part of the transport pathway, but specific sites in these linkers can interact directly or indirectly with parts of NaPi-IIa that undergo voltage-dependent conformational changes and thereby influence the voltage dependency of cotransport.

Download Full-text