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Comprender el mecanismo de la diol deshidratasa dependiente de B(12): una propuesta sinérgica retro-empujar-tirar
D M Smith1, B T Golding, L Radom
1Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
Journal of the American Chemical Society
|July 18, 2001
Resumen
Este estudio revela un nuevo mecanismo retro-push-pull para las reacciones de diol deshidratasa dependientes de la coenzima B12. La catálisis ácida y básica reduce sinérgicamente la barrera de migración hidroxilo, lo que explica la eficiencia de la enzima.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Química computacional es la química computacional.
- Catalización de enzimas por catalización de enzimas
Sus antecedentes:
- Las enzimas diol deshidratasa, dependientes de la coenzima B12, catalizan las reacciones cruciales de migración hidroxilo.
- El paso clave involucra radicales libres intermedios y un desplazamiento de 1,2-hidroxilo.
- Las barreras de migración no asistida son demasiado altas para explicar las tasas enzimáticas observadas.
Objetivo del estudio:
- Para investigar el mecanismo de las reacciones de diol deshidratasa dependientes de la coenzima B12 utilizando métodos computacionales.
- Para dilucidar el papel catalítico de las interacciones ácido-base en la etapa de migración hidroxilo.
Principales métodos:
- Ab initio se emplearon cálculos de la teoría de órbitas moleculares.
- Análisis de los radicales libres intermedios y estados de transición.
Principales resultados:
- La barrera de migración no asistida de 1,2-hidroxilo es prohibitivamente alta.
- Las interacciones ácidas ("retro-push") reducen significativamente la barrera de migración.
- Las interacciones básicas ("pull") también reducen la barrera.
- Una combinación sinérgica de efectos "empujar" y "tirar" reduce dramáticamente la barrera más allá de los efectos aditivos.
Conclusiones:
- El mecanismo retro-push-pull propuesto explica la alta eficiencia catalítica de la diol deshidratasa.
- Este mecanismo es consistente con los datos experimentales, incluido el etiquetado de isótopos y los estudios de tasa.
- La interacción sinérgica de la catálisis ácida y básica es clave para la función de las enzimas.
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