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Formación y estabilidad de los enolados peptídicos en solución acuosa
Ana Rios1, John P Richard, Tina L Amyes
1Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, USA.
Journal of the American Chemical Society
|July 11, 2002
Resumen
Este estudio cuantifica las tasas de desprotonación para los N-terminales del péptido, revelando que son significativamente más reactivos que los residuos internos. Esta diferencia es crucial para comprender la química de los péptidos y las proteínas.
Área de la Ciencia:
- Química biofísica y bioquímica.
- La cinética química es la cinética química.
- Química orgánica es la química orgánica.
Sus antecedentes:
- La estabilidad de los péptidos y las proteínas está influenciada por la reactividad de sus grupos terminales.
- Comprender la cinética de desprotonación de los carbonos alfa-amino es esencial para predecir el comportamiento químico.
Objetivo del estudio:
- Determinar las constantes de velocidad de segundo orden para la desprotonación de varios ácidos de carbono en D2O.
- Para estimar las tasas de transferencia de protones a los iones de hidróxido en H2O.
- Investigar los factores que influyen en la acidez de los carbonos alfa-amino y alfa-carbonilo en los péptidos.
Principales métodos:
- Medidas cinéticas utilizando el ion deuteroxido (D2O) para determinar las constantes de velocidad.
- Estimación de las constantes de velocidad de los iones de hidróxido en H2O.
- Análisis de correlación lineal entre log k ((HO) y ácido carbónico pKa.
Principales resultados:
- Se determinaron las constantes de velocidad de segundo orden (k ((DO)) para la desprotonación de los carbonos alfa-amino N-terminales e internos, así como de los carbonos acetilmetilo y alfa-amino en péptidos N-acetilados.
- Los valores estimados de pKa para estos ácidos de carbono oscilan entre 23,9 y 30,8.
- El carbono alfa-amino en un N-terminal protonado es aproximadamente 130 veces más reactivo que en un residuo interno.
Conclusiones:
- La mayor reactividad del grupo alfa-amino N-terminal se atribuye a una barrera intrínseca inferior de Marcus para la desprotonación de los ácidos carbónicos catiónicos alfa-carbonilo.
- A pesar de las diferencias en la fuerza de retirada de electrones, tanto los grupos catiónicos NH3 + como los neutrales NHAc disminuyen de manera similar el pKa de los ácidos carbónicos alfa-carbonilo.
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