scholarly journals The temperature-dependence of adenylate cyclase from baker's yeast

1979 ◽  
Vol 181 (3) ◽  
pp. 539-543 ◽  
Author(s):  
J Londesborough ◽  
K Varimo
Keyword(s):  
Reaction Mechanism ◽  
Adenylate Cyclase ◽  
Temperature Dependence ◽  
Reaction Rate ◽  
Arrhenius Plot ◽  
Maximum Velocity ◽  
Michaelis Constant ◽  
Arrhenius Plots ◽  
Temperature Range ◽  
Membrane Bound

The Michaelis constant of membrane-bound adenylate cyclase increased from 1.1 to 1.8 mM between 7 and 38 degrees C (delta H = 13 kJ/mol). Over this temperature range, the maximum velocity increased 10-fold, and the Arrhenius plot was nearly linear, with an average delta H* of 51 kJ/mol. The temperature-dependence of the reaction rate at 2 mM-ATP was examined in more detail: for Lubrol-dispersed enzyme, Arrhenius plots were nearly linear with average delta H* values of 45 and 68 kJ/mol, respectively, for untreated and gel-filtered enzymes; for membrane-bound enzyme, delta H changed from 40 kJ/mol above about 21 degrees C to 62 kJ/mol below 21 degrees C, but this behaviour does not necessarily indicate an abrupt, lipid-induced, transition in the reaction mechanism.

Arrhenius plot characteristics of adipocyte-plasma-membrane adenylate cyclase activity in lean and genetically obese (ob/ob) mice

1984 ◽  
Vol 4 (12) ◽  
pp. 1001-1008
Author(s):  
R. R. French ◽  
D. A. York
Keyword(s):  
Adenylate Cyclase ◽  
Plasma Membranes ◽  
Arrhenius Plot ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Obese Mice ◽  
Arrhenius Plots ◽  
Β Receptor ◽  
Lipid Environment ◽  
Adipocyte Plasma Membranes

Arrhenius plots of fluoride- and guanine-nucleotide-stimulated adenylate cyclase activity were linear in adipocyte plasma membranes from lean and obese (ob/ob) mice. Arrhenius plots of isoprenaline-stimulated adenylate cyclase activity in hepatic plasma membranes biphasic in both groups. The results were biphasic in membranes from Jean mice but linear in membranes from obese mice. In contrast, Arrhenius plots of glucagon-stimulated adenylate cyclase activity in hepatic plasma membranes were biphasic in both groups. The results suggest that the coupling between the β-receptor and the regulatory unit of adenylate cyclase, which has been observed to be defective in adipocyte plasma membranes from obese mice, is influenced by a different lipid environment in membranes from obese animals.

Radiation-induced reactions with cellulose. VII. Effect of temperature and substituted styrenes in the copolymerization process

1970 ◽  
Vol 23 (6) ◽  
pp. 1163 ◽  
Author(s):  
S Dilli ◽  
JL Garnett
Keyword(s):  
Reaction Mechanism ◽  
Temperature Dependence ◽  
Effect Of Temperature ◽  
Methoxy Derivative ◽  
Temperature Range ◽  
Hammett Constants ◽  
Radiation Induced ◽  
Radiation Induced Grafting ◽  
Electron Withdrawing Substituents

The temperature dependence of the radiation-induced grafting of styrene to cellulose has been studied. The system cellulose-styrene-methanol was examined in the temperature range from 40° to -196° in order to observe possible ionic contributions to the reaction mechanism. This effect was further investigated using a series of substituted styrenes containing both electron-donating and electron- withdrawing substituents. The 17 monomers used included o-, m-, and p-mono- halogenated styrenes, a number of alkylstyrenes and the p-methoxy derivative. An attempt has been made to correlate the grafting results with the Hammett constants for the substituent. The consumption of monomer during grafting of styrene to cellulose has also been investigated.

scholarly journals Kinetic studies of nitrogenase from soya-bean root-nodule bacteroids

1973 ◽  
Vol 131 (1) ◽  
pp. 61-75 ◽  
Author(s):  
F. J. Bergersen ◽  
G. L. Turner
Keyword(s):  
Reaction Mechanism ◽  
Protein Concentration ◽  
Root Nodule ◽  
Maximum Velocity ◽  
Kinetic Studies ◽  
Soya Bean ◽  
Michaelis Constant ◽  
Fe Protein ◽  
Catalytic Sites ◽  
Michaelis Constants

The apparent Michaelis constants [K′(N2) and K′(C2H2)] and the corresponding apparent maximum velocity values (V′) for soya-bean bacteroid nitrogenase increased concomitantly in response to increases in nitrogenase Fe–protein concentration and ATP concentration in cell-free assays and in response to O2 pressure in intact nodules and bacteroid suspensions. K′(C2H2) in cell-free assays was also affected by pH and by Na2S2O4 concentration. Nitrogenase Fe–protein behaved as a catalytic effector reacting at interacting sites on the nitrogenase Fe–Mo–protein. The results indicated that the Fe–Mo–protein probably bears the catalytic sites for N2 and C2H2 reduction. It is concluded that reduction of N2 or C2H2 by this nitrogenase involves a reaction mechanism with a sequence of unknown order. The sequence in which substrate, enzyme, effector, ATP and reductant react determines which of the various rate-constants are involved in the apparent Michaelis constant, whose true kinetic meaning was thus unresolved.

The Increased Sensitivity of Platelets to Prostacyclin in Marathon Runners

1984 ◽  
Vol 51 (03) ◽  
pp. 385-387 ◽  
Author(s):  
Clive J Dix ◽  
David G Hassall ◽  
K Richard Bruckdorfer
Keyword(s):  
Cardiovascular Disease ◽  
Endothelial Cells ◽  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Platelet Rich Plasma ◽  
Marathon Runners ◽  
Inhibition Of Platelet Aggregation ◽  
Increased Sensitivity ◽  
Membrane Bound

SummaryPlatelet-rich plasma was obtained 24 hr after the race ended from athletes who ran in the London marathon. The platelets were only marginally less sensitive to adrenaline than were those of non-runners using conventional aggregation tests. However, the runners’ platelets were much more sensitive to inhibition by prostacyclin, a prostaglandin synthesized by endothelial cells. It appeared that this effect was due to a greater activity in the platelets of the membrane-bound adenylate cyclase enzyme which generates intracellular cyclic AMP. Cyclic AMP production is known to be stimulated by prostacyclin and to cause the inhibition of platelet aggregation. The results indicate another possible protective effect of exercise against cardiovascular disease which is independent of the known changes in lipoprotein concentrations previously observed in athletes.

Specific features of the temperature dependence of tryptophan fluorescence lifetime in the temperature range of −170–20 °C

2020 ◽  
Vol 393 ◽  
pp. 112435
Author(s):  
Peter P. Knox ◽  
Vladimir V. Gorokhov ◽  
Boris N. Korvatovsky ◽  
Nadezhda P. Grishanova ◽  
Sergey N. Goryachev ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Fluorescence Lifetime ◽  
Tryptophan Fluorescence ◽  
Temperature Range

scholarly journals Three-component reaction involving isoquinoline and dimethyl acethylenedicarboxylate in the presence of indole: Theoretical and experimental investigations of the reaction mechanism

2021 ◽  
Vol 46 ◽  
pp. 146867832095686
Author(s):  
Mohammad Zakarianezhad ◽  
Sayyed Mostafa Habibi-Khorassani ◽  
Batoul Makiabadi ◽  
Elham Zeydabadi
Keyword(s):  
Reaction Mechanism ◽  
Potential Energy Surfaces ◽  
Reaction Rate ◽  
Product Configuration ◽  
Experimental Investigations ◽  
Uv Spectrophotometry ◽  
Three Component Reaction ◽  
Energy Surfaces ◽  
Theoretical Results ◽  
Reaction Rate Equation

The reaction kinetics among isoquinoline, dimethyl acetylenedicarboxylate, and indole (as NH-acid) were investigated using ultraviolet (UV) spectrophotometry. The reaction rate equation was obtained, the dependence of the reaction rate on different reactants was determined, and the overall rate constant ( kov) was calculated. By studying the effects of solvent, temperature, and concentration on the reaction rate, some useful information was obtained. A logical mechanism consistent with the experimental observations was proposed. Also, comprehensive theoretical studies were performed to evaluate the potential energy surfaces of all structures that participated in the reaction mechanism. Finally, the proposed mechanism was confirmed by the obtained results and the probable and logical reaction paths and also a correct product configuration were suggested based on the theoretical results.

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