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. 1982 Mar;69(3):591–596. doi: 10.1104/pp.69.3.591

Stimulation of Ammonia and 2-Oxoglutarate-Dependent O2 Evolution in Isolated Chloroplasts by Dicarboxylates and the Role of the Chloroplast in Photorespiratory Nitrogen Recycling

K C Woo 1, C Barry Osmond 1
PMCID: PMC426260  PMID: 16662255

Abstract

Intact chloroplasts isolated from spinach (Spinacia oleracea L.) leaves showed a light-dependent O2 evolution (5.5 ± 0.75 micromoles per milligram chlorophyll per hour) when supplied with ammonia and 2-oxoglutarate. This (ammonia, 2-oxoglutarate)-dependent O2 evolution was stimulated 2- to 4-fold by the dicarboxylates, malate, succinate, fumarate, glutarate, and l-tartarate. Evolution of O2 in the presence of malate was dependent on the presence of both 2-oxoglutarate and NH4Cl; malate with only either 2-oxoglutarate and NH4Cl alone did not support O2 evolution. Furthermore, in the presence of malate, the amount of O2 evolved was solely dependent on the amount of NH4Cl or 2-oxoglutarate added and malate did not affect the ratio of O2 evolved to NH4Cl or 2-oxoglutarate consumed. Studies with inhibitors (2-(3,4-dichlorophenyl)-1,1-dimethyl urea, methionine sulfoximine, and azaserine) indicated that the above activity was directly linked to glutamine synthetase and glutamate synthase activity in the chloroplast and was not caused by the metabolism of malate. The Vmax/2 of (ammonia, 2-oxoglutarate)-dependent O2 evolution was reached at 32 micromolar NH4Cl and 6 millimolar (approximately) 2-oxoglutarate in the absence of malate, and at 22 micromolar NH4Cl and 73 micromolar 2-oxoglutarate when malate (3 millimolar) was present.

Intact chloroplasts isolated from pea (Pisum sativum) leaves also showed a stimulation of (ammonia, 2-oxoglutarate)-dependent O2 evolution by malate. However glutamine was required for this activity even though glutamine with only either NH4Cl or 2-oxoglutarate did not respond to malate stimulation.

The measured rates of (ammonia, 2-oxoglutarate)-dependent O2 evolution in isolated spinach chloroplasts in the presence of malate were about 19.5 ± 4.5 micromoles O2 evolved per milligram chlorophyll per hour. This is adequate to sustain photorespiratory NH3 recycling and the refixation of NH3 arising from NO3 under ambient conditions in the light. The role of the chloroplast in photorespiratory NH3 recycling and the nature of the associated transport of 2-oxoglutarate into the chloroplast is discussed.

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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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