15N-Ammonia Assimilation, 2-Oxoglutarate Transport, and Glutamate Export in Spinach Chloroplasts in the Presence of Dicarboxylates in the Light 1
AUTOR(ES)
Woo, K. C.
RESUMO
The direct incorporation of 15NH4Cl into amino acids in illuminated spinach (Spinacia oleracea L.) chloroplasts in the presence of 2-oxoglutarate plus malate was determined. The amido-N of glutamine was the most highly labeled N-atom during 15NH4 assimilation in the presence of malate. In 4 minutes the 15N-label of the amido-N of glutamine was 37% enriched. In contrast, values obtained for both the N-atom of glutamate and the amino-N of glutamine were only about 20% while that of the N-atom of aspartate was only 3%. The addition of malate during the assimilation of 15NH4Cl and Na15NO2 greatly increased the 15N-label into glutamine but did not qualitatively change the order of the incorporation of 15N-label into all the amino acids examined. This evidence indicates the direct involvement of the glutamine synthetase/glutamate synthase pathway for ammonia and nitrite assimilation in isolated chloroplasts. The addition of malate or succinate during ammonia assimilation also led to more than 3-fold increase in [14C]2-oxoglutarate transport into the chloroplast as well as an increase in the export of [14C]glutamate out of the chloroplast. Little [14C]glutamine was detected in the medium of the chloroplast preparations. The stimulation of 15N-incorporation and [14C]glutamate export by malate could be directly attributed to the increase in 2-oxoglutarate transport activity (via the 2-oxoglutarate translocator) observed in the presence of exogenous malate.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1054311Documentos Relacionados
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