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Efectos de isótopos cinéticos para la transferencia concertada de protones múltiples: un estudio de dinámica directa
Zorka Smedarchina1, Willem Siebrand, Antonio Fernández-Ramos
1Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6. Zorka.Smedarchina@nrc.ca
Journal of the American Chemical Society
|January 8, 2003
Resumen
La anhidrasa carbónica II también es conocida como anhidrase carbónica II.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Química computacional es la química computacional.
- La cinética de las enzimas.
Sus antecedentes:
- La anhidrase carbónica II es crucial para eliminar el dióxido de carbono de los fluidos corporales.
- Se conoce la estructura del sitio activo de la enzima, pero la disposición de la molécula de agua no está clara.
- La transferencia de protones a través de puentes de agua es el paso que limita la velocidad.
Objetivo del estudio:
- Para calcular la constante de velocidad de reacción para la anhidrasa carbónica II utilizando un modelo de sitio activo.
- Para investigar el mecanismo de la transferencia de protones, incluido el túnel.
- Para comparar resultados computacionales con datos experimentales.
Principales métodos:
- Modelado del sitio activo utilizando 58 átomos, incluido un ion de zinc y metilimidazol.
- Teoría funcional de densidad aproximada (SCC-DFTB) para cálculos de estructura y campo de fuerza.
- Cálculos de dinámica directa con el método instantáneo aproximado y la teoría del estado de transición variacional.
Principales resultados:
- Un solo estado de transición sugiere una triple transferencia concertada de protones.
- Los cálculos cuánticos muestran tasas y KIE más altas que los experimentos.
- Los cálculos clásicos arrojan tasas más bajas pero KIEs significativamente más altos.
- El túnel se confirma como el mecanismo principal para la transferencia de protones.
- Un modelo de puente de dos aguas, aunque de baja concentración, es altamente eficiente para el transporte de protones.
Conclusiones:
- La transferencia de protones en la anhidrase carbónica II se produce a través de un túnel a través de un puente de dos aguas.
- El mecanismo de puente de dos aguas es esencial para la alta eficiencia catalítica de la enzima.
- La transferencia concertada está respaldada por la dependencia de KIE de la concentración de deuterio.
- Este mecanismo difiere de las isoenzimas menos eficientes que pueden usar transferencia gradual.
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