, Volume 162, Issue 3, pp 220-225

First online:

Properties of phosphoenolpyruvate carboxylase in desalted extracts from isolated guard-cell protoplasts

  • H. SchnablAffiliated withInstitut für Botanik der Technischen Universität
  • , C. KottmeierAffiliated withInstitut für Botanik der Technischen Universität

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Properties of phosphoenolpyruvate (PEP) carboxylase (EC obtained from isolated guard-cell protoplasts of Vicia faba L. were determined following rapidly desalting of the extract on a Sephadex G 25 column. The activity of PEP carboxylase was measured as a function of PEP and malate concentration, pH and K+ concentration within 2–3 min after homogenization of the guard-cell protoplasts. The activity of this enzyme was stimulated by PEP concentrations of 0.1 to 0.75 mM and by K+ ions (12 mM), but inhibited by PEP concentrations above 1 mM and by malate. Changes in the Km(PEP) and Vmax values with increasing malate concentrations (2.5 and 5 mM) indicate that the malate level, varying in relation to the physiological state of guard cells, plays an important role in regulating the properties of phosphoenolpyruvate carboxylase.

Key words

Guard cell protoplast Malate sensitivity Phosphoenolpyruvate carboxylase Protoplast (guard cell) Vicia (guard cells)