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Un estado superoxo-ferroso en un estado reducido de hemoproteínas oxíferas y compuestos modelo
Roman Davydov1, James D Satterlee, Hiroshi Fujii
1Department of Chemistry, Northwestern University, 2156 Sheridan Road, Evanston, Illinois 60208-3113, USA.
Journal of the American Chemical Society
|December 25, 2003
Resumen
La criorreducción del oxihemo genera un estado superoxo-ferroso ([FeO2]sup7), distinto de la forma previamente asumida como peroxo-ferrico ([FeO2]per7). Este intermediario superoxo-ferroso es el producto de reducción primario y se convierte en estados peroxo/hidroperoxo-ferrosos al calentarse.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Química bioorgánica Química bioorgánica.
- La espectroscopia es una técnica de espectroscopia.
Sus antecedentes:
- Numerosas investigaciones han caracterizado los centros [FeO2]7 como peroxo-ferrico ([FeO2]per7), donde un ferrihemo se une a un peroxo-ligando dianiónico.
- Este estado peroxo-ferrico se entiende heurísticamente si el padre [FeO2]6 es visto como un centro superoxo-ferrico con el electrón agregado localizado en la fracción O-O.
Objetivo del estudio:
- Para investigar las propiedades de los centros [FeO2]7 generados por criorreducción de varios complejos oxy-heme.
- Para determinar la estructura electrónica y la localización de la densidad de espín de estos intermediarios oxihemo-reducidos.
- Para aclarar el producto de reducción primario y sus transformaciones posteriores.
Principales métodos:
- Se realizaron experimentos de resonancia paramagnética de electrones (EPR) y de doble resonancia nuclear de electrones (ENDOR).
- La criorreducción a 77 K se utilizó para generar las especies reducidas de oxihema.
- Se llevaron a cabo estudios con oxihemoglobina monomérica (oxy-GMH3), porfirina de octaetil ferroso oxigenado y un modelo de hemo (ciclideno).
Principales resultados:
- Los experimentos EPR/ENDOR revelaron que los centros [FeO2]7 producidos son "superoxo-ferrosos" ([FeO2]sup7) y no peroxo-ferrosos.
- Casi la unidad de densidad de espín se localizó en un extremo de la porción superoxo coordinado con un ion ferroso de espín bajo.
- Las especies [FeO2]sup7 se convierten en peroxo/hidroperoxo-ferrico ([FeO2H]7) intermedios después del recocido por encima de 150 K.
Conclusiones:
- El producto de reducción primario de la criorreducción de oxihemo es la especie superoxoferrosa ([FeO2]sup7).
- La transición redox interna a los estados peroxo/hidroperoxo-ferrico está influenciada por factores ambientales como el enlace H y la donación de protones.
- Estos hallazgos desafían las caracterizaciones anteriores y proporcionan una nueva comprensión de los intermediarios de reducción del hemo.
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