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Organo-vanadatos pentavalentes como análogos de estado de transición para las reacciones de transferencia de
June M Messmore1, Ronald T Raines
1Contribution from the Department of Biochemistry and Department of Chemistry , University of Wisconsin-Madison, Madison, WI 53706.
Journal of the American Chemical Society
|March 23, 2011
Resumen
Los organo-vanadatos pentavalentes como la uridina 2 son también pentavalentes.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- La cinética de las enzimas.
- Biología química Biología química.
Sus antecedentes:
- Los organo-vanadatos pentavalentes se proponen como análogos del estado de transición para las reacciones de transferencia de fosforilo.
- Se supone que el vanadato uridina 2',3'-cíclico (U>v) imita el estado de transición de la ribonucleasa A (RNasa A).
- Lys41 en RNasa A es crucial para la estabilización del estado de transición a través de enlaces de hidrógeno.
Objetivo del estudio:
- Para probar experimentalmente la hipótesis de que U>v es un análogo de estado de transición para RNasa A.
- Para investigar el grado en que U>v se asemeja al estado de transición catalítica de la RNasa A.
- Evaluar la utilidad de los organo-vanadatos pentavalentes en el análisis riguroso del estado de transición.
Principales métodos:
- Mutagénesis y semisíntesis dirigidas al sitio para crear variantes de RNasa A en Lys41.1.
- Los ensayos de cinética enzimática miden las velocidades catalíticas (kcat/Km) y las constantes de inhibición (Ki).
- Análisis de las propiedades analógicas del estado de transición utilizando gráficos logKi vs log(Km/kcat).
Principales resultados:
- Las variantes de RNasa A en Lys41 mostraron grandes diferencias en la actividad catalítica (10^5 veces) pero diferencias más pequeñas en la inhibición de U>v (<40 veces).
- LogKi vs log ((Km/kcat) las parcelas produjeron pendientes entre 0.25 y 0.36, desviándose del valor ideal de la unidad.
- Los valores de Ki para U>v mostraron una débil correlación con las constantes de unión sustrato/producto.
Conclusiones:
- El vanadato uridina 2',3'-cíclico (U>v) es un análogo del estado de transición marginal para la ribonucleasa A (RNasa A).
- Los organo-vanadatos pentavalentes no siempre pueden servir como análogos precisos del estado de transición para las reacciones de transferencia de fosforilo.
- El estudio destaca las limitaciones en el uso de vanadatos para el análisis detallado del estado de transición en la catálisis enzimática.
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