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Nitrito e hidroxilamina como sustratos de la nitrogenasa: implicaciones mecanicistas para la vía de reducción de N2

Sudipta Shaw¹, Dmitriy Lukoyanov, Karamatullah Danyal

¹Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322, United States.

Journal of the American Chemical Society

|August 20, 2014

Resumen

La nitrogenasa reduce el nitrito a amoníaco, revelando intermedios comunes con fijación de nitrógeno. Este estudio propone un mecanismo que involucra hidroxilamina e hidrazina, aclarando la liberación de amoníaco durante la catálisis de la nitrogenasa.

Área de la Ciencia:

La bioquímica es la bioquímica.
Enzimología Enzimología.
Química bioorgánica Química bioorgánica.

Sus antecedentes:

La nitrogenasa cataliza la reducción del nitrógeno (N2) a amoníaco (NH3), un paso crucial en el ciclo del nitrógeno.
La reducción de nitrito (NO2(-)) a amoníaco (NH3) por la nitrogenasa comparte similitudes mecánicas con la reducción de N2.
Comprender estas vías es clave para dilucidar los complejos mecanismos catalíticos de la nitrogenasa.

Objetivo del estudio:

Para investigar el mecanismo de reducción del nitrito por la nitrogenasa.
Para identificar y caracterizar los intermediarios de reacción en la reducción de NO2
Para comparar los intermediarios de reducción de NO2 (−) con los observados durante la reducción de N2.

Principales métodos:

La cinética de la enzima y el análisis estequiométrico de la reducción de NO2 (((-).
Utilizando técnicas de captura por congelación para aislar los intermediarios de reacción.
Empleando la espectroscopia de doble resonancia nuclear de electrones de banda Q (ENDOR) y la modulación de la envoltura de eco de espín de electrones (ESEEM) para caracterizar los intermedios.

Principales resultados:

Se identificaron dos intermediarios clave (H e I) durante la rotación de NO2 , idénticos a los de la reducción de N2.
Se propone la hidroxilamina (NH2OH) como un intermediario de reducción de NO2 y un sustrato para la nitrogenasa.
Se ha demostrado que la reducción de NO2(-) se produce a través de especies ligadas a la hidroxilamina y a la hidrazina, convergiendo con la vía de reducción de N2.

Conclusiones:

La reducción de nitrito por nitrogenaza comparte intermediarios comunes con la reducción de N2, lo que sugiere una estrategia catalítica conservada.
El mecanismo propuesto implica la formación de hidroxilamina y hidrazina unidas, evitando los intermediarios desfavorables.
La liberación de amoníaco en la fijación de N2 se produce después de la entrega de cinco electrones y protones a N2, con un total de siete transferidos al sitio activo de la enzima.

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