Estimation of the Kinetic Acidity from Substrate Conformation—Stereochemical Course of the Deprotonation of Cyclohexenyl Carbamates

2007 ◽  
Vol 46 (10) ◽  
pp. 1645-1649 ◽  
Author(s):  
Jochen Becker ◽  
Stefan Grimme ◽  
Roland Fröhlich ◽  
Dieter Hoppe
Keyword(s):  
Kinetic Acidity ◽  
Substrate Conformation

Solvolysis kinetics and mechanism of substituted 3-acetyl-1,3-diphenyltriazenes in acid medium; Kinetic acidity function

1987 ◽  
Vol 52 (9) ◽  
pp. 2212-2216
Author(s):  
Oldřich Pytela ◽  
Martin Kaska ◽  
Miroslav Ludwig ◽  
Miroslav Večeřa
Keyword(s):  
Acid Medium ◽  
Sulphuric Acid ◽  
Rate Constants ◽  
Decomposition Kinetics ◽  
Acidity Function ◽  
Hammett Equation ◽  
Kinetic Acidity ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Catalytic Rate

The decomposition kinetics has been measured of fourteen 3-acetyl-1,3-bis(subst. phenyl)triazenes in 40% (v/v) ethanol and sulphuric acid. The kinetic acidity function and catalytic rate constants have been determined from the rate constants observed. Mechanism has been suggested for the general acid-catalyzed solvolysis from comparison of the course of the kinetic acidity function and H0 function and from the reaction constant of the Hammett equation.

A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2021 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a refined enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

scholarly journals A Bacteroidetes locus dedicated to fungal 1,6-β-glucan degradation: Unique substrate conformation drives specificity of the key endo-1,6-β-glucanase

2017 ◽  
Vol 292 (25) ◽  
pp. 10639-10650 ◽  
Author(s):  
Max J. Temple ◽  
Fiona Cuskin ◽  
Arnaud Baslé ◽  
Niall Hickey ◽  
Gaetano Speciale ◽  
...  
Keyword(s):  
Substrate Conformation

Acidity of hydrocarbons. XLV. Kinetic acidity of ethylene towards cesium cyclohexylamide

1972 ◽  
Vol 13 (17) ◽  
pp. 1625-1628 ◽  
Author(s):  
M.J. Maskornick ◽  
A. Streitwieser
Keyword(s):  
Kinetic Acidity

ESR study of kinetic acidity of 6-tert-butyl-2-hydroxy-4-triphenylmethylphenoxyl

1993 ◽  
Vol 42 (1) ◽  
pp. 71-74 ◽  
Author(s):  
A. S. Masalimov ◽  
L. E. Melbardis ◽  
A. I. Prokof'ev
Keyword(s):  
Tert Butyl ◽  
Kinetic Acidity

Kinetic acidity of cubane

1991 ◽  
Vol 113 (1) ◽  
pp. 357-358 ◽  
Author(s):  
Richard E. Dixon ◽  
Andrew Streitwieser ◽  
Philip G. Williams ◽  
Philip E. Eaton
Keyword(s):  
Kinetic Acidity

scholarly journals Substrate Conformation Correlates with the Outcome of Hyoscyamine 6β-Hydroxylase Catalyzed Oxidation Reactions

2018 ◽  
Vol 140 (24) ◽  
pp. 7433-7436 ◽  
Author(s):  
Richiro Ushimaru ◽  
Mark W. Ruszczycky ◽  
Wei-chen Chang ◽  
Feng Yan ◽  
Yung-nan Liu ◽  
...  
Keyword(s):  
Oxidation Reactions ◽  
Substrate Conformation ◽  
Catalyzed Oxidation
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