scholarly journals Effect of temperature and pH on carbamoylation and phosphorylation of serum cholinesterases. Theoretical interpretation of activation energies in complex reactions

1972 ◽  
Vol 130 (2) ◽  
pp. 515-524 ◽  
Author(s):  
V. Simeon ◽  
E. Reiner ◽  
C. A. Vernon
Keyword(s):  
Human Serum ◽  
Rate Constants ◽  
Time Course ◽  
Organophosphorus Compounds ◽  
Horse Serum ◽  
Bimolecular Reaction ◽  
Effect Of Temperature ◽  
Theoretical Interpretation ◽  
Serum Cholinesterase ◽  
Kinetics Of

1. The effect of temperature and pH was studied on the kinetics of inhibition of horse serum and human serum cholinesterase by four organophosphorus compounds and five carbamates. 2. For all compounds, and at each pH and temperature, the inhibition followed the kinetics of a bimolecular reaction with the inhibitor in excess, and with a negligible concentration of the Michaelis complex. 3. The second-order rate constants (ka) for inhibition of human serum cholinesterase by one organophosphate and one carbamate increased from 5° to 40°C with an apparent activation energy of 46kJ/mol (11kcal/mol). 4. The ka constant for inhibition of horse serum cholinesterase increased with temperature from 5° to 30°C, and then decreased from 30° to 40°C. The theoretical interpretation of such an unusual effect of temperature is derived. 5. The increase of ka with pH (human serum cholinesterase) followed the dissociation curve for a single group on the enzyme (pK7.5). 6. Rate constants for decarbamoylation (k+3) were determined, and the time-course of inhibition was calculated from the ka and k+3 constants.

scholarly journals Studies of the acetylcholinesterase from houseflies (Musca domestica L.) resistant and susceptible to organophosphorus insecticides

1975 ◽  
Vol 149 (2) ◽  
pp. 463-469 ◽  
Author(s):  
A L Devonshire
Keyword(s):  
Musca Domestica ◽  
Rate Constants ◽  
Gel Electrophoresis ◽  
Organophosphorus Compounds ◽  
Organophosphorus Insecticides ◽  
Triton X ◽  
Kinetics Of ◽  
Kinetics Of Inhibition ◽  
Single Enzyme

Acetylcholinesterase from the heads of insecticide-resistant and -susceptible houseflies (Musca domestica L.) was studied in vitro. The enzymes could not be distinguished electrophoretically, and their behaviour on polyacrylamide-disc-gel electrophoresis was influenced by the presence of Triton X-100 in both the homogenate and the gels. In the absence of detergent, the acetylcholinesterase was heterogeneous, but behaved as a single enzyme when it was present. By analogy with studies of acetylcholinesterase from other sources, these observations were attributed to aggregation of the enzyme when not bound by membranes. The enzyme from resistant flies was more slowly inhibited than the susceptible enzyme, bimolecular rate constants (ki) differing by approx. 4-20-fold for a range of organophosphorus compounds. The kinetics of inhibition of acetylcholinesterase were consistent with the results of electrophoresis, i.e. they corresponded to those of a single enzyme in the presence of Triton X-100, but a mixture of enzymes in its absence. The susceptibility of the more sensitive components in these mixtures was determined.

Conversion between permeability states of IP3 receptors in cultured smooth muscle cells

1995 ◽  
Vol 269 (3) ◽  
pp. C813-C818 ◽  
Author(s):  
T. Sugiyama ◽  
W. F. Goldman
Keyword(s):  
Rate Constants ◽  
Time Course ◽  
Ip3 Receptors ◽  
A7r5 Cells ◽  
High Conductance State ◽  
Cultured Smooth Muscle Cells ◽  
Induced Changes ◽  
Kinetics Of ◽  
Best Fit ◽  
Conductance State

The kinetics of the effect of inositol 1,4,5-trisphosphate (IP3) on Ca2+ in the sarcoplasmic reticulum (SR) were studied in saponin-permeabilized A7r5 cells. At 0.1 microM, IP3 elicited slow monoexponential declines in SR free Ca2+ concentration ([Ca2+]SR). For IP3 concentration ([IP3]) = 0.2-100 microM, evoked declines in [Ca2+]SR were biphasic and best fit as the sum of two first-order processes with rate constants kfast and kslow. The kfast varied as a function of [IP3] over the range tested, whereas kslow was already maximal when [IP3] = 0.1 microM. To analyze SR Ca2+ release elicited by IP3, the rate constants for IP3-induced changes in the total SR Ca2+ content (kR) were calculated. kR was accurately described only when both [Ca2+]SR and [IP3] were considered together. kR was dependent on IP3 binding to receptors that existed in either of two states, a high-affinity low-conductance state (IP3RH) and a low-affinity high-conductance state (IP3RL). The permeability of IP3RL was 12.28 times larger than that of IP3RH, and the conversion between permeability states as well as changes in both the affinity and cooperativity with which IP3 was bound to IP3RL were mediated by SR Ca2+. This SR Ca(2+)-dependent modulation of the characteristics of IP3 receptors forms the basis for the biphasic time course characteristic of IP3-evoked SR Ca2+ release.

scholarly journals KINETICS OF THE REACTIONS BETWEEN ISOPROPYL CUMENE AND TERTIARY BUTYL CUMENE HYDROPEROXIDES AND IRON(II) IN DILUTE AQUEOUS SOLUTIONS IN THE ABSENCE OF OXYGEN

1952 ◽  
Vol 30 (12) ◽  
pp. 985-993 ◽  
Author(s):  
R. J. Orr ◽  
H. Leverne Williams
Keyword(s):  
Free Radicals ◽  
Rate Constants ◽  
Arrhenius Equation ◽  
Cumene Hydroperoxide ◽  
Bimolecular Reaction ◽  
Probable Error ◽  
Tertiary Butyl ◽  
Rate Of Reaction ◽  
Dilute Aqueous Solutions ◽  
Kinetics Of

From studies of the rate of reaction at 11°, 15°, 20°, and 26 °C. it was deduced that the bimolecular reaction between iron(II) and isopropyl cumene hydroperoxide is represented by[Formula: see text]At 0 °C. the radical induced oxidation of iron(II) due to inability of the monomer to remove the free radicals became appreciable. Addition of up to 7.5% methanol did not change the rate appreciably. The effect of traces of oxygen was negligible. Rate constants were measured at 15°, 9°, and 0 °C. for the reaction between iron(II) and the tertiary butyl cumene hydroperoxide. The average probable error in the determinations was 5.4%. From the data, the Arrhenius equation was determined as[Formula: see text]Comparison of the equations measured for cumene hydroperoxide, isopropyl cumene hydroperoxide, and tertiary butyl cumene hydroperoxide and iron(II) has been made. Changes in the constants have been explained qualitatively. The iodometric method of analysis when applied to tertiary butyl cumene hydroperoxide must be modified for accurate results. It is believed that the heating necessary in the presence of water decomposes the hydroperoxide.

ACTION OF ORGANOPHOSPHORUS COMPOUNDS UPON ESTERASES OF HUMAN LIVER

1963 ◽  
Vol 41 (1) ◽  
pp. 1537-1546 ◽  
Author(s):  
D. J. Ecobichon ◽  
W. Kalow
Keyword(s):  
Human Serum ◽  
Human Liver ◽  
Organophosphorus Compounds ◽  
Chemical Conversion ◽  
The Other ◽  
Serum Cholinesterase ◽  
Organophosphorus Insecticides ◽  
Low Concentrations ◽  
Starch Gel ◽  
Per Se

Human serum and liver esterases separated electrophoretically in starch gel were exposed to two series of organophosphorus insecticides. One series consisted of compounds active per se, the other of analogues requiring metabolic or chemical conversion to produce potent anticholinesterases. The results indicated that only one fraction of the liver, designated as zone L-2, is inhibited by low concentrations of all insecticides. This fraction shows a similar pattern of susceptibility to different inhibitors as does human serum cholinesterase. Of the other two zones of activity in liver, zone L-1 was found to be more susceptible to activated thionate, dithioate, and thioether derivatives than was zone L-3, while the latter zone was more susceptible to phosphates active per se.

ACTION OF ORGANOPHOSPHORUS COMPOUNDS UPON ESTERASES OF HUMAN LIVER

1963 ◽  
Vol 41 (7) ◽  
pp. 1537-1546 ◽  
Author(s):  
D. J. Ecobichon ◽  
W. Kalow
Keyword(s):  
Human Serum ◽  
Human Liver ◽  
Organophosphorus Compounds ◽  
Chemical Conversion ◽  
The Other ◽  
Serum Cholinesterase ◽  
Organophosphorus Insecticides ◽  
Low Concentrations ◽  
Starch Gel ◽  
Per Se

Human serum and liver esterases separated electrophoretically in starch gel were exposed to two series of organophosphorus insecticides. One series consisted of compounds active per se, the other of analogues requiring metabolic or chemical conversion to produce potent anticholinesterases. The results indicated that only one fraction of the liver, designated as zone L-2, is inhibited by low concentrations of all insecticides. This fraction shows a similar pattern of susceptibility to different inhibitors as does human serum cholinesterase. Of the other two zones of activity in liver, zone L-1 was found to be more susceptible to activated thionate, dithioate, and thioether derivatives than was zone L-3, while the latter zone was more susceptible to phosphates active per se.

scholarly journals The kinetics of oxidation of ferroperoxidase by molecular oxygen. A model of a terminal oxidase

1974 ◽  
Vol 141 (1) ◽  
pp. 265-272 ◽  
Author(s):  
Charles F. Phelps ◽  
Eraldo Antonini ◽  
Giorgio Giacometti ◽  
Maurizio Brunori
Keyword(s):  
Computer Simulation ◽  
Rate Constants ◽  
Time Course ◽  
Initial Rate ◽  
Time Range ◽  
Analogue Computer ◽  
Terminal Oxidase ◽  
Kinetics Of Oxidation ◽  
Rate Limiting ◽  
Kinetics Of

1. The decay of oxyferroperoxidase to ferriperoxidase was studied by rapidly mixing solutions of ferroperoxidase with various amounts of oxygen and following the time-course of appearance of oxyferroperoxidase and its subsequent decay to ferriperoxidase by reaction with ferroperoxidase. 2. The scheme can be accommodated by and [Formula: see text] and occurs without detectable intermediates being observed in the millisecond time-range. 3. Analogue-computer simulation of the reaction is in agreement with the initial rate-limiting reaction being an intermolecular, not intramolecular, electron-donating process, and analysis of the data leads to quantitative values for the rate constants of the overall process. 4. The reaction of oxyferroperoxidase with ferroperoxidase is a model of a terminal oxidase, and the results are discussed in terms of the possible importance of this reaction in peroxidase function, and also in the light it throws on autoxidation of haem compounds.

scholarly journals ON THE KINETICS OF POTENTIAL, ELECTROMOTANCE, AND CHEMICAL CHANGE IN THE EXCITABLE SYSTEM OF NERVE

1958 ◽  
Vol 42 (1) ◽  
pp. 193-229 ◽  
Author(s):  
Paul Mueller
Keyword(s):  
Chemical Equilibrium ◽  
Rate Constants ◽  
Time Course ◽  
Chemical Change ◽  
External Source ◽  
Analogue Computer ◽  
Experimental Conditions ◽  
Excitable System ◽  
Total Potential ◽  
Kinetics Of

The kinetics of interaction between potential, chemical equilibrium, and electromotance in the excitable system of nerve are analyzed. The theoretical system has the following properties: It gives rise to two electromotances each of which depends directly on a chemical equilibrium. The equilibria are determined by the potential across the system. After a sudden potential shift the equilibria reach their new value with an exponential time course, the time constant of which is determined by the rate constants of the two reactions. The rate constants are different due to different activation energies. The two electromotances give rise to potentials of opposite sign. The total potential produced by the system is equal to the sum of the two potentials. The two equilibria are thus determined by any externally applied potential as well as by the sum of the internally produced potentials. The dependence of the equilibria on the potential is calculated from first principles. The equations which describe this system are solved by an analogue computer, which gives instantaneous solutions of the total internal potential as a function of time and any voltage applied from an external source. Comparison between recorded and computed action potentials shows excellent agreement under all experimental conditions. The electromotances might originate from a Ca++—Na+—K+ exchange at fixed negative sites in the Schwann cell.

Influence of Radioiodine Therapy on Urinary Iodine Excretion

1998 ◽  
Vol 37 (03) ◽  
pp. 107-112 ◽  
Author(s):  
I. Lauer ◽  
M. Bähre ◽  
E. Richter ◽  
B. Melier
Keyword(s):  
Time Course ◽  
Radioiodine Therapy ◽  
Urinary Iodine ◽  
Target Volume ◽  
Urinary Iodine Excretion ◽  
Urinary Creatinine ◽  
Iodine Excretion ◽  
Kinetics Of ◽  
Persistent Elevation ◽  
Benign Thyroid

Summary Aim: In 214 patients with benign thyroid diseases the time-course of urinary iodine excretion (UIE) was investigated in order to identify changes after radioiodine therapy (RITh). Method: UIE was measured photometrically (cerium-arsenite method) and related to urinary creatinine on the first and last day of the radioiodine test and then three days, seven days, four weeks, and six months after 1311 administration. Results: As compared with the level found immediately before radioiodine therapy, median UIE had almost doubled four weeks after therapy and was still significantly elevated six months after therapy. This increase correlated significantly with the target volume as measured by scintigraphy and sonography. Conclusions: The persistent elevation of UIE for months after RITh is a measure of treatment-induced damage to thyrocytes. Therefore, in view of the unfavourable kinetics of iodine that follow it, RITh should if possible be given via a single-dose regime.

Effect of Calcium ion on the interaction between Thrombin and Heparin. Thermal Denaturation

1977 ◽  
Vol 38 (03) ◽  
pp. 0677-0684 ◽  
Author(s):  
Raymund Machovich ◽  
Péter Arányi
Keyword(s):  
Calcium Ions ◽  
Rate Constants ◽  
Thermal Denaturation ◽  
Time Course ◽  
Complex Analysis ◽  
Heat Inactivation ◽  
Second Phase ◽  
Denaturation Kinetics ◽  
Enzyme Protection ◽  
Enzyme Denaturation

SummaryHeat inactivation of thrombin at 54° C followed first order kinetics with a rate constant of 1.0 min−1 approximately. Addition of heparin resulted in protection against thermal denaturation and, at the same time, rendered denaturation kinetics more complex. Analysis of the biphasic curve of heat inactivation in the presence of heparin revealed that the rate constants of the second phase changed systematically with heparin concentrations. Namely, at 4.5 × 10−6M, 9 × 10−6M, 1.8 × 10−5M and 3.6 × 10−5M heparin concentrations, the rate constants were 0.27 min−1, 0.17 min−1, 0.11 min−1 and 0.06 min−1, respectively.Sulfate as well as phosphate ions displayed also enzyme protection against heat inactivation, however, the same effect was obtained already at a heparin concentration, lower by three orders of magnitude.The kinetics of enzyme denaturation was not affected by calcium ions, whereas in the presence of heparin the inactivation rate of thrombin changed, i. e. calcium ions abolished the biphasic character of time course of thermal denaturation.Thus, the data suggest that calcium ions contribute to the effect of heparin on thrombin.

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