Efecto del telurito (TeO3-2) sobre los complejos citocromo oxidasa bo y bd-I de Escherichia coli en condiciones aeróbicas
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Archivos
Fecha
2012
Autores
Profesor/a Guía
Facultad/escuela
Idioma
es
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Universidad Andrés Bello
Nombre de Curso
Licencia CC
Licencia CC
Resumen
La cadena transportadora de electrones (CTE) constituye una vía convergente de productos formados en la vía glicolitica y el ciclo de Krebs en E. coil. Aun cuando se sabe que el telurito afecta directamente estas vías, en relación con la CTE se ha observado una disminución en los niveles de ATP y cambios en el gradiente transmembrana (ApH), sugiriendo que probablemente podría ser otro de los blancos de este oxianión de teluro. Conocer los efectos del telurito sobre la CTE permitiría completar una visión global del funcionamiento del metabolismo central de E. coli en estas condiciones. Este trabajo de Tesis apuntó a estudiar el efecto que en particular ejerce el telurito sobre los complejos citocromo oxidasa bo y bd-I de E. coli en condiciones aeróbicas de crecimiento.
Se encontró que la exposición de la bacteria a concentraciones subletales del tóxico genera un estado de estrés oxidativo que afecta el normal funcionamiento de la CTE, en que las oxidasas terminales disminuyen su actividad viéndose particularmente afectado el complejo citocromo bo. Se observó que la expresión de los genes que especifican el citocromo bo disminuye, sugiriendo que el telurito afectaría no sólo la actividad de este complejo, sino que además el nivel de sus transcritos. Como se esperaba, se observó además la inducción de genes involucrados en respuesta a estrés oxidativo. Sin embargo y dada la gran toxicidad del telurito, aparentemente la célula llevaría a cabo un drástico cambio orientándose a un metabolismo de tipo anaeróbico para así aliviar los efectos provocados por la exposición a telurito. Finalmente, se determinó que membranas de E. coil reducen telurito en una reacción dependiente de NADH que no es inhibida por KCN, poniendo en duda la participación de las oxidaras terminales.
The electron transport chain (ETC) is a pathway to which E. coli glycolytic as well as Krebs cycle products converge. Although it is known that tellurite affects directly these metabolic routes, decreased ATP levels and transmembrane pH gradient changes have been observed regarding the ETC suggesting that it probably represents another target of the tellurium oxyanion. Knowing the tellurite effects on the ETC would allow getting a global vision on the E. coli central metabolism functioning in these conditions. In this Thesis work, the particular effect of tellurite on the E. coli bo and bd-I cytochrome oxidase complexes was studied under aerobic conditions. It was found that cell exposure to sub lethal tellurite concentrations results in the establishment of an oxidative stress status that affects the normal ETC functioning, with decreased activity of the terminal oxidases, particularly the cytochome bo complex. Decreased expression of genes encoding this complex was also observed, showing that tellurite not only affects its activity but also their transcripts level. As expected, induction of genes involved in the response to oxidative stress was observed. However and given the great toxicity of tellurite, the cell would change drastically to an anaerobic-like metabolism to alleviate the effects derived from tellurite exposure. Finally, it was determined that E. coli membranes are able to reduce tellurite in a NADH-dependent, KCN-insensitive reaction, suggesting that terminal oxidases are not involved.
The electron transport chain (ETC) is a pathway to which E. coli glycolytic as well as Krebs cycle products converge. Although it is known that tellurite affects directly these metabolic routes, decreased ATP levels and transmembrane pH gradient changes have been observed regarding the ETC suggesting that it probably represents another target of the tellurium oxyanion. Knowing the tellurite effects on the ETC would allow getting a global vision on the E. coli central metabolism functioning in these conditions. In this Thesis work, the particular effect of tellurite on the E. coli bo and bd-I cytochrome oxidase complexes was studied under aerobic conditions. It was found that cell exposure to sub lethal tellurite concentrations results in the establishment of an oxidative stress status that affects the normal ETC functioning, with decreased activity of the terminal oxidases, particularly the cytochome bo complex. Decreased expression of genes encoding this complex was also observed, showing that tellurite not only affects its activity but also their transcripts level. As expected, induction of genes involved in the response to oxidative stress was observed. However and given the great toxicity of tellurite, the cell would change drastically to an anaerobic-like metabolism to alleviate the effects derived from tellurite exposure. Finally, it was determined that E. coli membranes are able to reduce tellurite in a NADH-dependent, KCN-insensitive reaction, suggesting that terminal oxidases are not involved.
Notas
Tesis (Bioquímico, Magíster en Bioquímica)
Palabras clave
Telurio, Escherichia Coli, Investigaciones.