<b>Catalysis by Secondary Valence Forces</b>

Swain, C. Gardner; Taylor, Lynn J.

doi:10.1021/ja00871a041

Cited by 14 publications

(15 citation statements)

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“…To explore the origin of the catalytic power of methyltransferases, it is important to have a clear idea about the activation barrier of the reaction in both environments enzymatic and aqueous solution. Swain and Taylor have reported experimental values of 30.1 kcal/mol for the activation free energy of the reaction of trimethylsulfonium ion (CH 3 ) 3 S + and a phenolate ion in aqueous solution at 80°C. Using their reported activation entropy we estimated the effect of temperature change and obtained an estimate of

{(Δ g_{normalw}^{‡})}_{obs}

= 30.8 kcal/mol at 25°C (Table ).…”

Section: Resultsmentioning

confidence: 99%

Methyltransferases do not work by compression, cratic, or desolvation effects, but by electrostatic preorganization

et al. 2015

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The enzyme catechol O-methyltransferase (COMT) catalyzes the transfer of a methyl group from S-adenosylmethionine to dopamine and related catechols. The search for the origin of COMT catalysis has led to different proposals and hypothesis, including the entropic, the NAC and the compression proposals as well as the more reasonable electrostatic idea. Thus it is important to understand the catalytic power of this enzyme and to examine the validity of different proposals and in particularly the repeated recent implication of the compression idea. The corresponding analysis should be done by well-defined physically based analysis that involves computations rather than circular interpretations of experimental results. Thus we explore here the origin of the catalytic efficiency of COMT by using the empirical valence bond and the linear response approximation approaches. The results demonstrate that the catalytic effect of COMT is mainly due to electrostatic preorganization effects. It is also shown that the compression, NAC and entropic proposals do not account for the catalytic effect.

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{(Δ g_{normalw}^{‡})}_{obs}

= 30.8 kcal/mol at 25°C (Table ).…”

Section: Resultsmentioning

confidence: 99%

Methyltransferases do not work by compression, cratic, or desolvation effects, but by electrostatic preorganization

et al. 2015

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“…The overall reaction is nearly thermoneutral with a forward barrier of 37.3 kcal/mol. The experimental barrier has not been determined for the reaction of catecholate ion with trimethylsulfonium ion, but the enthalpy barrier for the reaction between phenolate ion and trimethyl sulfonium ion has been determined to be 28.5 kcal/mol at 80 °C . It is known that phenolate ion is more basic in aqueous solution than catecholate ion.…”

Section: Resultsmentioning

confidence: 99%

A Theoretical Examination of the Factors Controlling the Catalytic Efficiency of a Transmethylation Enzyme: Catechol O-Methyltransferase

Zheng

Bruice

1997

J. Am. Chem. Soc.

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The reaction mechanism of the nonenzymatic transmethylation of catechol by S-adenosylmethionine (AdoMet, as modeled by sulfonium ion) has been elucidated using ab initio and semiempirical quantum mechanical methods. The gas phase reaction between catecholate and sulfonium is extremely fast, involving no overall barrier. The reaction profile to some extent resembles a typical gas phase SN2 reaction. However, in aqueous solution, this reaction is very slow with a predicted barrier of 37.3 kcal/mol. The calculated (k H/k D)α, k 12/k 13, k 16/k 18, and k 32/k 34 are 0.80, 1.06, 1.003, and 1.010, respectively. Previously, Schowen and co-workers measured (k H/k D)α and k 12/k 13 to be 0.83 ± 0.05 and 1.09 ± 0.05 for the catechol O-methyltransferase (COMT)-catalyzed methylation of 3,4-dihydroxyacetophenone by AdoMet. This good agreement between the calculated kinetic isotope effects for the model reaction and the measured kinetic isotope effects for the enzymatic reaction seems to suggest that the structure of the enzymatic transition state is very similar to that of the nonenzymatic reaction. Factors that modulate the catalytic efficacy of catechol O-methyltransferase were discussed in light of the present study on the nonenzymatic reaction and the recently solved X-ray crystal structure.

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“…Not being a proponent of the merged elimination mechanism, he (28) later stated that the order of thermodynamic affinity for hydrogen or carbon was methoxide or hydroxide greater than thiophenoxide whereas the order of kinetic reactivity toward hydrogen or carbon was thiophenoxide greater than the alkoxide ions. Swain (29) thought the second order reaction of thiophenoxide with benzyldimethylsulfonium ion in water at 80° appears to be accelerated by ancillary molecular bonding of the complex or charge transfer type .at the transition state.…”

Section: Introduction Of An Electron-attracting B-substituentmentioning

confidence: 99%

Bimolecular elimination reactions of cyclopentyl compounds

Smith

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Catalysis by Secondary Valence Forces

Cited by 14 publications

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Methyltransferases do not work by compression, cratic, or desolvation effects, but by electrostatic preorganization

Methyltransferases do not work by compression, cratic, or desolvation effects, but by electrostatic preorganization

A Theoretical Examination of the Factors Controlling the Catalytic Efficiency of a Transmethylation Enzyme: Catechol O-Methyltransferase

Bimolecular elimination reactions of cyclopentyl compounds

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