scholarly journals The carboxybiotin complex of chicken liver pyruvate carboxylase. A kinetic analysis of the effects of acetyl-CoA, Mg2+ ions and temperature on its stability and on its reaction with 2-oxobutyrate

1986 ◽  
Vol 235 (2) ◽  
pp. 359-364 ◽  
Author(s):  
P V Attwood ◽  
J C Wallace
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Protein Conformation ◽  
Pyruvate Carboxylase ◽  
Activation Parameters ◽  
Slow Phase ◽  
Acetyl Coa ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Pseudo First Order

The enzyme-[14C]carboxybiotin complex of chicken liver pyruvate carboxylase has been isolated and shown to be relatively stable, with a half-life at 0 degree C of 342 min. The kinetic properties of the decay of this complex, in both the presence and the absence of the substrate analogue, 2-oxobutyrate, have been examined. The data for the reaction with 2-oxobutyrate at 0 degree C fitted a biphasic exponential decay curve, enabling the calculation of rate constants for both the fast and slow phases of the reaction at this temperature. The effect of temperature on the observed pseudo-first-order rate constant for the slow phase of the reaction with 2-oxobutyrate, and that for the decay of the enzyme-[14C]carboxybiotin complex alone, have been examined. Arrhenius plots of these data revealed that the processes being studied in each type of experiment were single reactions represented by one rate constant in each case. For the decay of the enzyme-[14C]carboxybiotin complex in the absence of 2-oxobutyrate, the rate-determining process may be the movement of carboxybiotin from the site of the first partial reaction to the site of the second. The calculated thermodynamic activation parameters indicate that this reaction is accompanied by a large change in protein conformation. With 2-oxobutyrate present, the observed process in the slow phase of the reaction was probably the dissociation of the carboxybiotin from the first subsite. Here, the activation parameters suggest that a much smaller change in protein conformation accompanies this reaction. Both sets of experiments were also performed in the presence of acetyl-CoA, but this activator had little effect on the measured thermodynamic activation parameters. However, in both cases the observed pseudo-first-order rate constants in the presence of acetyl-CoA were about 75% of those in its absence. The effects of Mg2+ on the reaction kinetics of the enzyme-[14C]carboxybiotin complex with 2-oxobutyrate were similar to those observed with the sheep enzyme by Goodall, Baldwin, Wallace & Keech [(1981) Biochem. J. 199, 603-609].

Effects of oxidant concentration and temperature on decolorization of azo dye: comparisons of UV/Fenton and UV/Fenton-like systems

2012 ◽  
Vol 65 (11) ◽  
pp. 1970-1974 ◽  
Author(s):  
C. Y. Kuo ◽  
C. Y. Pai ◽  
C. H. Wu ◽  
M. Y. Jian
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Azo Dye ◽  
Activation Energies ◽  
First Order ◽  
First Order Kinetics ◽  
Oxidant Concentration ◽  
Decolorization Efficiency ◽  
Pseudo First Order ◽  
Reactive Red 2

This study applies photo-Fenton and photo-Fenton-like systems to decolorize C.I. Reactive Red 2 (RR2). The oxidants were H2O2 and Na2S2O8; Fe2+, Fe3+, and Co2+ were used to activate these two oxidants. The effects of oxidant concentration (0.3–2 mmol/L) and temperature (25–55 °C) on decolorization efficiency of the photo-Fenton and photo-Fenton-like systems were determined. The decolorization rate constants (k) of RR2 in the tested systems are consistent with pseudo-first-order kinetics. The rate constant increased as oxidant concentration and temperature increased. Activation energies of RR2 decolorization in the UV/H2O2/Fe2+, UV/H2O2/Fe3+, UV/Na2S2O8/Fe2+ and UV/Na2S2O8/Fe3+ systems were 32.20, 39.54, 35.54, and 51.75 kJ/mol, respectively.

Kinetics and mechanism of aminolysis of (Z)-4-arylidene-2-phenyl-5(4H)oxazolones

1992 ◽  
Vol 70 (10) ◽  
pp. 2515-2519 ◽  
Author(s):  
Sharifa S. Alkaabi ◽  
Ahmad S. Shawali
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Order Conditions ◽  
Kinetics And Mechanism ◽  
Hammett Equation ◽  
Third Order ◽  
First Order ◽  
Different Temperatures ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of the reactions of a series of (Z)-4-arylidene-2-phenyl-5(4H)oxazolones 1 with n-butylamine and piperidine were studied spectrophotometrically in dioxane, ethanol, and cyclohexane under pseudo-first-order conditions and at different temperatures. The relation k1(obs) = k2[amine] + k3[amine]2 was found applicable for all reactions studied in either dioxane or ethanol. However, in cyclohexane the n-butylaminolysis of 1 followed only third-order kinetics k1(obs) = k3[n-BuNH2]2. The kinetics of the reaction of 1 with n-butylamine in the presence of catalytic amounts of triethylamine in dioxane followed the equation: k1(obs)k2 = [n-BuNH2] + k3[n-BuNH2]2[Formula: see text] [Et3N]. The rate constants k2 and k3 correlated well with the Hammett equation and the corresponding activation parameters were determined. The results were interpreted in terms of a mechanism involving solvent- and amine-catalyzed processes.

scholarly journals The carboxybiotin complex of pyruvate carboxylase. A kinetic analysis of the effects of Mg2+ ions on its stability and on its reaction with pyruvate

1984 ◽  
Vol 219 (1) ◽  
pp. 243-251 ◽  
Author(s):  
P V Attwood ◽  
J C Wallace ◽  
D B Keech
Keyword(s):  
Pyruvate Carboxylase ◽  
General Scheme ◽  
Order Rate Constant ◽  
Enzymic Activity ◽  
Slow Phase ◽  
First Order ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Pseudo First Order ◽  
Rate Limiting

The enzyme-[14C] carboxybiotin complex of sheep liver pyruvate carboxylase was isolated and the reaction between this and pyruvate was studied by using the quenched-flow rapid-reaction technique. At 0.5 degrees C the reaction was 80% complete within 180 ms. The reaction was monophasic and obeyed pseudo-first-order kinetics. Increasing concentrations of Mg2+ caused a decrease in the magnitude of the observed pseudo-first-order rate constant. Throughout the carboxylation of pyruvate, the rate-limiting step of the reaction occurred after the dissociation of carboxybiotin from the first sub-site, whereas in the slow phase of the reaction with 2-oxobutyrate this dissociation is the rate-limiting step. It is possible, from the reaction scheme proposed, that the inhibition of overall enzymic activity by high concentrations of Mg2+ could be caused by the transfer of the carboxy group from biotin to pyruvate becoming rate-limiting. The efficacy of a substrate as a signal for the movement of carboxybiotin from the first sub-site is reflected by the amount that the effective affinity of the enzyme- carboxybiotin complex for Mg2+ is lowered. In the presence of the substrates tested, the affinities of the carboxybiotin complex can be arranged in order of increasing magnitude, i.e.: (formula; see text). The kinetics of the decay of the enzyme-[14C] carboxybiotin complex at 0 degree C in the absence of substrates are similar to the reaction with pyruvate except that the carboxybiotin is also unstable in the first sub-site, to some degree. This similarity allows for the proposal of a general scheme for the decarboxylation of the enzyme- carboxybiotin complex in the presence or in the absence of substrates.

scholarly journals Kinetic Isotope Effects in the Chromium(VI) Oxidation of Bicyclic Alcohols

1999 ◽  
Vol 23 (2) ◽  
pp. 146-147
Author(s):  
J. Hodge Markgraf ◽  
Jordan S. Dubow ◽  
Jessica A. Charland ◽  
Elliott H. Sohn
Keyword(s):  
Rate Constants ◽  
Acidic Solution ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Kinetic Isotope Effects ◽  
Secondary Alcohols ◽  
First Order ◽  
Chromium Vi ◽  
Kinetic Isotope ◽  
Pseudo First Order

Pseudo first-order rate constants are determined for the oxidation of a series of secondary alcohols and their monodeutero analogues by ammonium chromate in aqueous acidic solution at several temperatures; the relative rates and activation parameters are consistent with a cyclic, symmetrical transition state.

Activation parameters for the reconstitution of apotyrosinase by copper

1993 ◽  
Vol 71 (1-2) ◽  
pp. 96-98 ◽  
Author(s):  
Donald C. Wigfield ◽  
Douglas M. Goltz
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Divalent Copper ◽  
First Order ◽  
Order Rate ◽  
Entropy Of Activation ◽  
Pseudo First Order ◽  
Fold Excess

The reaction of apotyrosinase with divalent copper to give enzymatically active tyrosinase has been studied at pH 8.2 and temperatures from 278 to 303 K. At a 10-fold excess of Cu(II) over enzyme, the pseudo-first order rate constants range from 1.32 × 10−3 s−1 to 2.93 × 10−2 s−1 and yield activation parameters of ΔH≠ = 85 ± 3 kJ∙mol−1 and ΔS≠ = 5 ± 20 J∙mol−1∙K−1. The near zero value for the entropy of activation is discussed.Key words: tyrosinase, copper.

Kinetics and mechanism of the base hydrolysis of some trans-dihalogeno(cyclam)rhodium(III) complexes

1978 ◽  
Vol 56 (5) ◽  
pp. 709-713 ◽  
Author(s):  
H. L. Chung ◽  
E. J. Bounsall
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
The Other ◽  
Base Hydrolysis ◽  
Trans Effect ◽  
First Order ◽  
Class B ◽  
Pseudo First Order ◽  
Hydrolysis Of ◽  
Kinetic Class

The base hydrolysis of trans-[Rh(cyclam)XY]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane; X− and Y− = Cl−, Br−, and I−) are studied in aqueous solution over a range of OH− concentration and at various temperatures. The kinetics are done at a constant ionic strength with excess of [OH−] (smallest ratio = 200:1) so that pseudo first order rate constants are obtained for all the determinations. All of the reactions proceed with complete retention of configuration, and no trans-to-cis isomerization is found. The kinetic trans effect of these complexes is I− > Br− > Cl− on a rate basis, but based on ΔH≠, I− > Br− = Cl−. These Rh(III) complexes exhibit kinetic class (b) character on the ΔH≠ basis. The results of the rate constants and the activation parameters are interpreted in ternis of an SN1CB mechanism. The behavior of these complexes is compared to that of the other analogous complexes.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

A kinetic standard for precise calibration of spectrophotometer cell temperature.

1981 ◽  
Vol 27 (5) ◽  
pp. 753-755 ◽  
Author(s):  
P A Adams ◽  
M C Berman
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Cell Temperature ◽  
First Order ◽  
Order Rate ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

Abstract We describe a simple, highly reproducible kinetic technique for precisely measuring temperature in spectrophotometric systems having reaction cells that are inaccessible to conventional temperature probes. The method is based on the temperature dependence of pseudo-first-order rate constants for the acid-catalyzed hydrolysis of N-o-tolyl-D-glucosylamine. Temperatures of reaction cuvette contents are measured with a precision of +/- 0.05 degrees C (1 SD).

On the Chemical Reactivity of the Phytochrome Chromophore in the Pr and Pfr Form

1985 ◽  
Vol 40 (3-4) ◽  
pp. 215-218 ◽  
Author(s):  
Fritz Thümmler ◽  
Peter Eilfeld ◽  
Wolfhart Rüdiger ◽  
Doo-Khil Moon ◽  
Pill-Soon Song
Keyword(s):  
Reaction Kinetics ◽  
Rate Constants ◽  
Chemical Reactivity ◽  
Order Reaction ◽  
First Order Reaction ◽  
Limiting Factor ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo First Order ◽  
The Difference

The reactivity of the phytochrome chromophore and related tetrapyrroles towards ozone and tetranitromethane was investigated. Both oxidizing reagents cause bleaching of the main absorp­tion band of the pigment. The rate constants for this bleaching were determined under conditions of pseudo first order reaction kinetics. The rate constants for the reaction with ozone are similar for native phytochrome and for freely accessible tetrapyrroles (biliverdin, small chromopeptides from phytochrome) indicating that accessibility is not the limiting factor for the reaction with ozone. Under a variety of conditions, the Pfr chromophore reacts by about 10% faster than the Pr chromophore. This may reflect the true difference in reactivity. The rate constants for the reaction with tetranitromethane are much larger for biliverdin, bilirubin and small chromopeptides from phytochrome than for native phytochrome. The limiting factor for this reaction in native phytochrome therefore is the accessibility of the chromophore by the reagent. Previous conclusions on the difference in exposure of the tetrapyrrole chromophore in Pr and Pfr are confirmed.

Sign in / Sign up

Export Citation Format

Share Document