Actividad proteolítica asociada a la pared celular
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El fluido extracelular (EF), conteniendo proteínas solubles y unidas iónicamente a la pared celular, fue extraído de hipocótilos etiolados de poroto. Se observó que, durante el alargamiento de los hipocótilos, disminuyó la cantidad de proteínas y se produjeron cambios significativos en el patrón polipeptídico del EF, sugiriendo la presencia de proteasas asociadas a la pared celular. Se determinó a diferentes pHs la actividad proteolítica presente en el mismo, observándose una actividad endopeptidasa ácida, con un máximo a pH 4,5. Dicha endopeptidasa fue aislada del resto de las proteínas presentes en el EF por cromatografía de afinidad, en un gel de hemoglobina-agarosa. La enzima aislada presentó alta estabilidad térmica y temporal, además de dependencia de cofactores metálicos. La endopeptidasa parece ser una enzima monomérica, con una masa molecular aproximada de 52 kDa, que tiene como sustrato a numerosas proteínas extracelulares. La actividad endopeptidasa aumentó durante el crecimiento de los hipocótilos, hasta alcanzar su máximo valor durante la fase exponencial de elongación. Posteriormente, la actividad disminuyó, sugiriendo alguna función en la regulación del alargamiento.
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