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. 1982 Nov;70(5):1514–1517. doi: 10.1104/pp.70.5.1514

Evidence for the Glutamine Synthetase/Glutamate Synthase Pathway during the Photorespiratory Nitrogen Cycle in Spinach Leaves

K C Woo 1, J F Morot-Gaudry 1,1, R E Summons 1, C Barry Osmond 1
PMCID: PMC1065915  PMID: 16662707

Abstract

Spinach leaf (Spinacia oleracea L.) discs infiltrated with [15N]glycine were incubated at 25°C in the light and in darkness for 0, 30, 60 and 90 minutes. The kinetics of 15N-incorporation into glutamine, glutamate, asparagine, aspartate, and serine from [15N]glycine was determined. At the beginning of the experiment, just after infiltration (0 min incubation) serine, and the amido-N of glutamine and asparagine were the only compounds significantly labeled in both light- and dark-treated leaf discs. Incorporation of 15N-label into the other amino acids was observed at longer incubation time. The per cent 15N-enrichment in all amino acids was found to increase with incubation. However, serine and the amido-N of glutamine remained the most highly labeled products in all treatments. The above pattern of 15N-labeling suggests that glutamine synthetase was involved in the initial refixation of 15NH3 derived from [15N]glycine oxidation in spinach leaf discs.

The 15N-enrichment of the amino-N of glutamine was found to increase rapidly from 0 to 19% during incubation in the light. There was a comparatively smaller increase (4-9%) in the 15N-label of the amino-N of glutamine in tissue incubated in darkness. Furthermore the total flux of 15N-label into each of the amino acids examined was found to be greater in tissue incubated in the light than those in the dark. The above evidence indicates the involvement of the glutamine synthetase/glutamate synthase pathway in the recycling of photorespiratory NH3 during glycine oxidation in spinach leaves.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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