Phosphoenolpyruvate Carboxykinase Assayed at Physiological Concentrations of Metal Ions Has a High Affinity for CO2\ud

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Chen, Z. ; Walker, R.P. ; Acheson, R.M. ; Leegood, R.C. (2002)
  • Subject:
    mesheuropmc: inorganic chemicals

The effect of Mn2+/Mg2+ concentration on the activity of intact, homogeneous phosphoenolpyruvate carboxykinase (PEPCK) from leaves of the C4 grass, Guinea grass (Panicum maximum), have been investigated. Assay conditions were optimized so that PEPCK activity could be measured at concentrations of Mn2+/Mg2+ similar to those found in the cytosol (low micromolar Mn2+ and millimolar Mg2+). PEPCK activity was totally dependent on Mn2+ and was activated at low micromolar concentrations of Mn2+ by millimolar concentrations of Mg2+. Therefore, at physiological concentrations of Mn2+, PEPCK has a requirement for Mg2+. Assay at physiological concentrations of Mn2+/Mg2+ led to a marked decrease in its affinity for ATP and a 13-fold increase in its affinity for CO2. The Km (CO2) was further decreased by assay at physiological ATP to ADP ratios, reaching values as low as 20 μM CO2, comparable with the Km (CO2) of ribulose 1,5-bisphosphate carboxylase-oxygenase. This means that PEPCK will catalyze a reversible reaction and that it could operate as a carboxylase in vivo, a feature that could be particularly important in algal CO2-concentrating systems.\ud
  • References (5)

    1 This research was supported by the Biotechnology and Biological Sciences Research Council, UK (research grant nos. CO5229 and RSP07804), by a David Phillips Research Fellowship to R.P.W., and by a research studentship to R.M.A.

    2 These authors contributed equally to the paper.

    * Corresponding author; e-mail rob.walker@shef.ac.uk; fax 44 - 114 -222- 0002.

    Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.010431.

    Planta 195: 58-63 Wingler A, Walker RP, Chen Z-H, Leegood RC (1999) Phosphoenolpyruvate carboxykinase is involved in the decarboxylation of aspartate in the bundle-sheath of maize. Plant Physiol120: 539-545 Yazaki Y, Asukagawa N, Ishikawa Y, Ohta E, Sakata M (1988) Estimation of cytoplasmic free Mg2 levels and phosphorylation potentials in mung bean root tips by in vivo 31P NMR spectroscopy. Plant Cell Physiol 29: 919-924 Yeoh H-H, Badger MR, Watson L (1980) Variation in Km(CO2) of ribulose-1,5-bisphosphate carboxylase among grasses. Plant Physiol 66: 1110-1112 Yeoh H-H, Badger MR, Watson L (1981) Variations in kinetic properties of ribulose-1,5-bisphosphate carboxylases among plants. Plant Physiol 67: 1151-1155

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