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El inventario de electrones, la asignación cinética (E(n)), la estructura y el enlace de los intermediarios del

Hong-In Lee¹, Morten Sørlie, Jason Christiansen

¹Department of Chemistry Education, Kyungpook National University, Daegu, 702-701, Korea. leehi@knu.ac.kr

Journal of the American Chemical Society

|November 10, 2005

Resumen

El intermediario de la nitrogenasa S(EPR1), que probablemente contiene etileno unido al cofactor hierro-molibdeno, se identifica como un complejo de productos. Este estudio correlaciona los intermediarios enzimáticos con esquemas cinéticos, definiendo sus estados electrónicos.

Área de la Ciencia:

La bioquímica es la bioquímica.
Química bioorgánica Química bioorgánica.
La cinética de las enzimas.

Sus antecedentes:

Las enzimas nitrogenasas son cruciales para la fijación biológica del nitrógeno.
La comprensión del mecanismo de reducción del sustrato por la nitrogenasa requiere una caracterización detallada de los intermediarios de reacción.
El cofactor hierro-molibdeno (FeMo) es el sitio activo para la conversión del sustrato.

Objetivo del estudio:

Para dilucidar la estructura y el estado electrónico del intermedio S(EPR1) en la nitrogenasa.
Para correlacionar los intermediarios enzimáticos con modelos cinéticos establecidos como el esquema Lowe-Thorneley.
Para definir el estado químico del cofactor FeMo durante la rotación del sustrato.

Principales métodos:

Espectroscopia de doble resonancia electrónico-nuclear de alto campo (ENDOR) (1H y 57Fe).
Técnicas de Ondas Continuas (CW) y Mims pulsada ENDOR. técnicas de ondas continuas (CW) y Mims pulsada ENDOR.
Enriquecimiento isotópico con 57Fe.

Principales resultados:

El intermedio S(EPR1) se identifica como un complejo de productos, probablemente con etileno (C2H4) unido como ferraciclo al cofactor FeMo.
El cofactor FeMo en S(EPR1) exhibe valencias similares al intermedio ligado al CO, reducido en 2 electrones (m=2).
Se introduce un nuevo concepto, "inventario de electrones", para correlacionar los intermedios con los estados de reducción de Lowe-Thorneley, asignando S(EPR1) a E(n=4) y lo-CO a E(n=2).

Conclusiones:

Este estudio proporciona la primera correlación entre un estado cinético de Lowe-Thorneley y un estado químico definido de la enzima nitrogenasa.
Los hallazgos aclaran el modo de unión del etileno y la configuración electrónica del cofactor FeMo durante la rotación de la nitrogenasa.
El "inventario de electrones" proporciona un marco para comprender la distribución de electrones en los intermediarios de la nitrogenasa.

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