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Diurnal Changes in the Regulatory Properties of Phosphoenolpyruvate Carboxylase in CAM Plants: Are Alterations in the Quaternary Structure Involved?
Author(s) -
Krüger I.,
Kluge M.
Publication year - 1988
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1988.tb00007.x
Subject(s) - phosphoenolpyruvate carboxylase , phosphoenolpyruvate carboxykinase , allosteric regulation , protein quaternary structure , crassulacean acid metabolism , biochemistry , enzyme , pyruvate carboxylase , chemistry , ultracentrifuge , in vivo , biology , protein subunit , photosynthesis , microbiology and biotechnology , gene
Day — and night‐forms of phosphoenolpyruvate carboxylase (EC 4.1.1.31) (PEP‐C) were extracted from leaves of the CAM plant Kalanchoë daigremontiana . During storage after extraction, the day‐form spontaneously lost its sensitivity towards the allosteric inhibitor l ‐malate. This effect was accelerated by inorganic phosphate, PEP, 3‐PGA and G‐6‐P. l ‐Malate however stabilized the malate sensitivity of the day‐form of PEP‐C. Crude desalted extracts of the day‐form and of the night‐form of PEP‐C were subjected to ultracentrifugation on a continuous sucrose gradient in the presence of malate and of marker enzymes. Both forms of PEP‐C were found to have relative molecular masses of about 200,000. This suggests that both forms represent the dimers of the enzyme protein. The result also suggests that reversible dissociation and association of enzyme subunits is not the mechanism which brings about the interconversion of the two PEP‐C forms during the diurnal CAM cycle in vivo .