Mechanism of the reaction catalyzed by the catalytic subunit of aspartate transcarbamylase. Kinetic studies with acetyl phosphate as substrate

Biochemistry ◽  
1973 ◽  
Vol 12 (23) ◽  
pp. 4727-4732 ◽  
Author(s):  
Elizabeth Heyde ◽  
J. F. Morrison
Keyword(s):  
Kinetic Studies ◽  
Catalytic Subunit ◽  
Acetyl Phosphate ◽  
Aspartate Transcarbamylase ◽  
Mechanism Of The Reaction

scholarly journals Kinetics and proposed mechanism of the reaction of an immunoinhibition, particle-enhanced immunoassay

1997 ◽  
Vol 43 (12) ◽  
pp. 2384-2389 ◽  
Author(s):  
John C Thompson ◽  
Alan R Craig ◽  
Carol L Davey ◽  
David J Newman ◽  
Michele L Lonsdale ◽  
...  
Keyword(s):  
Monoclonal Antibody ◽  
Maximum Rate ◽  
Colloidal Stability ◽  
Kinetic Studies ◽  
Latex Agglutination ◽  
Equivalence Point ◽  
Colloidal Aggregation ◽  
Free Sample ◽  
Identical Fashion ◽  
Mechanism Of The Reaction

Abstract We report kinetic studies on the reaction of a latex agglutination immunoassay used to quantify phenytoin in serum. In this assay, polystyrene particles with a covalently attached analog of phenytoin react with an antiphenytoin monoclonal antibody to form light-scattering aggregates, with the rate of this reaction being decreased by addition of phenytoin from sample. In the absence of free (sample) phenytoin, this reaction did not exhibit a maximum rate of agglutination in the presence of excess antibody, i.e., an equivalence point. Furthermore, agglutination was inhibitable by free phenytoin even when the latter was added after agglutination of particles with antibody had begun. Most significantly, the immunoagglutination proceeded in an identical fashion with monovalent F(ab) fragment. These data are consistent with low-affinity immunospecific particle–antibody complexation, which then induces colloidal aggregation, without requiring immunospecific bridging by antibody molecules. The described mechanism is not generalizable to all latex agglutination immunoassays, although disturbance of colloidal stability may be a component in most assays.

N-Heterocyclic Carbene-Catalyzed Synthesis of Ynones via C–H Alkynylation of Aldehydes with Alkynyliodonium Salts

2019 ◽  
Author(s):  
Adam A. Rajkiewicz ◽  
Natalia Wojciechowska ◽  
Marcin Kalek
Keyword(s):  
Density Functional ◽  
Bond Formation ◽  
Kinetic Studies ◽  
Density Functional Theory Calculations ◽  
Hypervalent Iodine ◽  
Functional Theory ◽  
Leaving Group ◽  
13C Labelling ◽  
Reaction Proceeds ◽  
Mechanism Of The Reaction

Alkynylation of aldehydes with alkynyl(aryl)iodonium salts catalyzed by an N-heterocyclic carbene (NHC) has been developed. The application of the organocatalyst and the hypervalent iodine group-transfer reagent allowed for metal-free C–H functionalization and C–C bond formation. The reaction proceeds under exceptionally mild conditions, at –40 ⁰C and in the presence of an amine base, providing access to an array of heteroaryl-propargyl ketones containing various substituents in good to excellent yields. The mechanism of the reaction was investigated by means of both experiments and density functional theory calculations. 13C-labelling and computations determined that the key alkynyl transfer step occurs via an unusual direct SN2 substitution of iodine-based leaving group by Breslow intermediate nucleophile at an acetylenic carbon. Moreover, kinetic studies revealed that the turnover-limiting step of the catalytic cycle is the generation of the Breslow intermediate, whereas the subsequent C–C bond-formation is a fast process. These results were fully reproduced and rationalized by the computed full free energy profile of the reaction, showing that the largest energy span is located between protonated NHC and the transition state for the carbene attack on the aldehyde substrate.<br>

scholarly journals Chemical cross-linking of cyclic AMP-dependent protein kinase and its dissimilar subunits

1983 ◽  
Vol 209 (3) ◽  
pp. 581-586 ◽  
Author(s):  
J P Charlton ◽  
C H Huang ◽  
L C Huang
Keyword(s):  
Protein Kinase ◽  
Cyclic Amp ◽  
Ternary Complex ◽  
Kinetic Studies ◽  
Catalytic Subunit ◽  
Regulatory Subunit ◽  
Cross Linking ◽  
Dependent Protein Kinase ◽  
Native Form ◽  
Dependent Protein

Previous kinetic studies have demonstrated that the activation of cyclic AMP-dependent protein kinase by cyclic AMP involves the formation of a ternary complex of cyclic AMP, the regulatory subunit (R) and the catalytic subunit (C). It is suggested that only this ternary complex breaks down to liberate the enzymically active catalytic subunit. We have performed cross-linking experiments with the holoenzyme and its dissimilar subunits in the presence of MgATP and various concentrations of cyclic AMP. Results from these cross-linking studies indicate that regulatory subunits exist as dimers in the native form. Moreover, dissociation of the holoenzyme or the reconstituted enzyme is promoted by cyclic AMP, and the effect of MgATP is to stabilize the enzyme in the tetrameric form. The success in cross-linking the regulatory and the catalytic subunits of protein kinase with the lysine-specific bifunctional cross-linking reagent dimethyl suberimidate may be attributed to the presence of a large number of lysine residues in the enzyme.

The Mechanism of the Alkali catalysed Phenol-Formaldehyde reaction

1955 ◽  
Vol 8 (2) ◽  
pp. 194 ◽  
Author(s):  
JS Fitzgerald ◽  
RJL Martin
Keyword(s):  
Induction Period ◽  
Aldol Condensation ◽  
Phenol Formaldehyde ◽  
Kinetic Studies ◽  
Bimolecular Reaction ◽  
Hydrogen Ion ◽  
Catalysed Reaction ◽  
Alkaline Reaction ◽  
Cannizzaro Reaction ◽  
Mechanism Of The Reaction

Kinetic studies on the 2,3,4,5-tetramethylphenol(prehnitenol)- and 2,6-xylenol-formaldehyde reactions indicate that the alkali catalysed reaction is not a simple bimolecular reaction. The rate of the 2,6-xylenol-formaldehyde reaction in the presence of excess alkali has been shown to be proportional to [phenoxide]1.4 [formaldehyde]1.4 [free alkali]-0.4. The mechanism of the reaction has been interpreted as a reaction between the phenoxide ion and CH2=O together with other simultaneous reactions. It is unlikely that the +CH2OH plays any part in the alkali catalysed reaction. Attempts have been made to interpret the results on the basis that a hemiformal rearranges to a phenol alcohol and that the ion +CH2OPh reacts with a phenoxide ion. In any case it is not possible to give a complete mechanism with certainty. The degree of formation of hemiformal is too small to be detected by hydrogen ion measurements. When the Cannizzaro reaction of formaldehyde is carried out in the presence of a phenol, the phenoxide Ions catalyse a condensation which 1s presumably an aldol condensation. This reaction having a long induction period and being autocatalytic does not assume importance In the early stages of the reaction. A compound, probably 2,2'-dihydroxy-3,3',4,4',5,5',6,6'-octamethyldiphenylmethane, has been isolated from the alkaline reaction between prehnitenol and formaldehyde.

Kinetics and Mechanism of the Reaction of 2-Mercaptobenzothiazole with N-(Cyclohexylthio)Phthalimide and Related Compounds

1972 ◽  
Vol 45 (6) ◽  
pp. 1513-1531 ◽  
Author(s):  
P. N. Son ◽  
K. E. Andrews ◽  
A. T. Schooley
Keyword(s):  
Thermal Instability ◽  
Room Temperature ◽  
Kinetic Studies ◽  
Kinetics And Mechanism ◽  
Related Compounds ◽  
Mechanism Of The Reaction

Abstract Kinetic studies show that 2-mercaptobenzothiazole (MBT) reacts faster with N-(cyclohexylthio)phthalimide (CPT) than with such accelerators as N-t-butyl-2-benzothiozolesulfenamide (BBTS) or 2-(4-morpholinothio)benzothiazole (OBTS). Furthermore, the reaction between N-(cyclohexylthio)-o-benzoic sulfimide (CTBS) and MBT is so fast that it reacts almost instantaneously even at room temperature. However, CTBS is not a good retarder due to its thermal instability.

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