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Videos de Conceptos Relacionados

Radical Reactivity: Overview01:11

Radical Reactivity: Overview

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Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

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Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak...
2.3K
Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

2.6K
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
2.6K
Radical Formation: Addition00:47

Radical Formation: Addition

2.3K
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an...
2.3K
Radical Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

2.7K
Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For...
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Transfer RNA Synthesis02:36

Transfer RNA Synthesis

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One of the unique features of tRNA is the presence of modified bases. In some tRNAs, modified bases account for nearly 20% of the total bases in the molecule. Altogether, these unusual bases protect the tRNA from enzymatic degradation by RNases.
Each of these chemical modifications is carried by a specific enzyme, post-transcription. All of these enzymes have unique base and site-specificity. Methylation, the most common chemical modification, is carried by at least nine different enzymes, with...
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Monitoring Equilibrium Changes in RNA Structure by 'Peroxidative' and 'Oxidative' Hydroxyl Radical Footprinting
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Monitoring Equilibrium Changes in RNA Structure by 'Peroxidative' and 'Oxidative' Hydroxyl Radical Footprinting

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Transferencia de radicales conformacionalmente dinámica dentro de la reductasa de ribonucleótidos

Brandon L Greene1, Alexander T Taguchi2, JoAnne Stubbe2

  • 1Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138, United States.

Journal of the American Chemical Society
|October 18, 2017
PubMed
Resumen

Las reductasas de ribonucleótidos utilizan la transferencia radical para la reducción de nucleótidos. Este estudio muestra que la flexibilidad de las proteínas permite un transporte radical más rápido, crucial para la función enzimática.

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Área de la Ciencia:

  • La bioquímica
  • Enzimología
  • Dinámica de las proteínas

Sus antecedentes:

  • Las ribonucleótidos reductasas (RNR) son enzimas esenciales para la síntesis de ADN.
  • Los RNR de clase 1a utilizan un mecanismo de transferencia de radicales (RT) que incluye un radical tiilo de cisteína.
  • La transferencia radical ocurre a través de la interfaz de la subunidad α2:β2 a través de la transferencia de electrones acoplados a protones (PCET).

Objetivo del estudio:

  • Investigar el papel de la dinámica conformacional en la transferencia de radicales RNR.
  • Caracterizar el mecanismo de transferencia de radicales en el mutante R411A de E. coli clase 1a RNR.
  • Determinar la cinética de la transferencia radical a través de la interfaz de la subunidad.

Principales métodos:

  • Mutagénesis dirigida al sitio (R411A).
  • La supresión del codón ámbar para instalar la 3-amino tirosina (NH2Y) como una trampa de radicales.
  • Espectroscopia HYSCORE para estudiar el estado radical atrapado.
  • Generación de radicales fotoquímicos para estudios cinéticos.

Principales resultados:

  • La mutación R411A, que interrumpe el enlace H de Y731, retiene la actividad enzimática, lo que indica flexibilidad conformacional.
  • Y731 en el mutante R411A reforma dinámicamente los enlaces H, lo que permite la propagación de la transferencia radical.
  • La transferencia radical a través de la interfaz es conformacionalmente dependiente, con tasas crecientes en el mutante R411A.
  • Y731 cambios conformacionales ocurren en la escala de tiempo ns-μs, más rápido que la velocidad catalítica.

Conclusiones:

  • La flexibilidad conformacional de los residuos de tirosina es fundamental para la transferencia eficiente de radicales en RNR.
  • La reformación dinámica del enlace H facilita la propagación radical a lo largo de la vía PCET.
  • La cinética de las enzimas está modulada por la interacción entre la dinámica de las proteínas y el transporte de radicales.