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Effects of Phosphorylation on Phosphoenolpyruvate Carboxykinase from the C4 Plant Guinea Grass

Walker, R.P., Chen, Z., Acheson, R.M. and Leegood, R.C. (2002) Effects of Phosphorylation on Phosphoenolpyruvate Carboxykinase from the C4 Plant Guinea Grass. Plant Physiology, 128 (1). pp. 165-172. ISSN 0032-0889

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Abstract

In the C4 plant Guinea grass (Panicum maximum), phosphoenolpyruvate carboxykinase (PEPCK) is phosphorylated in darkened leaves and dephosphorylated in illuminated leaves. To determine whether the properties of phosphorylated and non-phosphorylated PEPCK were different, PEPCK was purified to homogeneity from both illuminated and darkened leaves. The final step of the purification procedure, gel filtration chromatography, further separated phosphorylated and non-phosphorylated forms. In the presence of a high ratio of ATP to ADP, the non-phosphorylated enzyme had a higher affinity for its substrates, oxaloacetate and phosphoenolpyruvate. The activity of the non-phosphorylated form was up to 6-fold higher when measured at low substrate concentrations. Comparison of proteoloytically cleaved PEPCK from Guinea grass, which lacked its N-terminal extension, from yeast (Saccharomyces cerevisiae), which does not possess an N-terminal extension, and from the C4 plant Urochloa panicoides, which possesses an N-terminal extension but is not subject to phosphorylation, revealed similar properties to the non-phosphorylated full-length form from Guinea grass. Assay of PEPCK activity in crude extracts of Guinea grass leaves, showed a large difference between illuminated and darkened leaves when measured in a selective assay (a low concentration of phosphoenolpyruvate and a high ratio of ATP to ADP), but there was no difference under assay conditions used to estimate maximum activity. Immunoblots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels showed no difference in the abundance of PEPCK protein in illuminated and darkened leaves. There were no light/dark differences in activity detected in maize (Zea mays) leaves, in which PEPCK is not subject to phosphorylation.

Item Type: Article
Copyright, Publisher and Additional Information: © 2002 American Society of Plant Biologists
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > School of Biological Sciences (Sheffield) > Department of Animal and Plant Sciences (Sheffield)
The University of Sheffield > University of Sheffield Research Centres and Institutes > Robert Hill Institute (Sheffield)
Depositing User: Repository Officer
Date Deposited: 13 Oct 2004
Last Modified: 06 Jun 2014 06:38
Status: Published
Refereed: Yes
URI: http://eprints.whiterose.ac.uk/id/eprint/140

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