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Mecanismo para la oxigenación de seis electrones de arilo-N por la enzima diironio no hemo CmlI

Anna J Komor, Brent S Rivard, Ruixi Fan¹

¹Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.

Journal of the American Chemical Society

|May 21, 2016

Resumen

La biosíntesis del cloranfenicol (CAM) implica una oxidación en varios pasos catalizada por CmlI. Un ciclo catalítico propuesto explica cómo la enzima utiliza oxígeno e intermedios para lograr la oxidación final de seis electrones para la producción de CAM.

Área de la Ciencia:

La bioquímica
Enzimología
Química orgánica

Sus antecedentes:

La biosíntesis de cloranfenicol (CAM) culmina en una oxidación de seis electrones de un precursor de aril-amina (NH2-CAM) al grupo aril-nitro.
Esta reacción es catalizada por la no hemo diiron oxigenasa CmlI, que forma un peroxo intermedio (P) al reaccionar con O2.

Objetivo del estudio:

Para aclarar el mecanismo de la oxidación de seis electrones en la biosíntesis CAM.
Determinar el papel del peroxo intermedio CmlI (P) e identificar otros oxidantes o intermedios potenciales.

Principales métodos:

Se utilizó la espectrometría de masas para analizar los productos de reacción en condiciones variables de isótopos de oxígeno ((18) O2 y (16) O2).
Se realizaron reacciones de recambio único para estudiar la oxidación catalizada por CmlI de NH2-CAM y sus intermedios.

Principales resultados:

La espectrometría de masas confirmó que ambos átomos de oxígeno en el grupo nitro CAM se originan a partir de O2.
La presencia de ambos (18) O y (16) O en CAM bajo condiciones específicas indicó la reformación del peroxo intermedio (P).
El intermediario NH-OH-CAM fue identificado como el reductor responsable de reformar el racimo diferencial de CmlI.

Conclusiones:

Se propone un ciclo catalítico en el que el NH2-CAM se oxida a NH(OH) -CAM, que luego vuelve a reducir el CmlI, permitiendo la reformación de P.
El P reformado luego oxida NH ((OH) -CAM a NO-CAM y posteriormente a CAM, incorporando un segundo átomo de O2.
La oxidación completa de seis electrones ocurre dentro del sitio activo, requiriendo solo dos electrones exógenos.

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