title: Partial purification and characterization of a protein inhibitor of phosphoenolpyruvate carboxylase kinase.
abstract: The activity of phosphoenolpyruvate carboxylase (PEPCase) kinase in leaf extracts increased markedly on dilution. This was shown to be caused by the presence of a protein that inhibits the kinase. The inhibitor protein was separated from the kinase and purified partially. It inhibited the kinase reversibly, presumably by a direct interaction; it was neither a protease nor a protein phosphatase. The amounts of kinase and inhibitor in leaves were estimated following separation by hydrophobic chromatography. The amount of inhibitor in the crassulacean acid metabolism plant Kalanchoe fedtschenkoi Hamet et Perrier was sufficient to inhibit the basal level of kinase activity present during the light period and the early stages of the dark period. Similarly, the amount of inhibitor in the C4 plant Zea mays L. was sufficient to inhibit the low amount of kinase activity present in the dark and at moderate light intensity. Analogous to the role of the protein inhibitor of mammalian cyclic AMP-dependent protein kinase, the function of the PEPCase kinase inhibitor may be to inhibit the basal level of kinase present in conditions under which rapid flux through PEPCase is not required.
authors.affiliation: Division of Biochemistry and Molecular Biology, University of Glasgow, UK.
authors.forename: G A
authors.initials: GA
authors.lastname: Nimmo
authors.forename: M B
authors.initials: MB
authors.lastname: Wilkins
authors.forename: H G
authors.initials: HG
authors.lastname: Nimmo
mesh_terms: D002918:Chymotrypsin / Q000494:pharmacology; D029627:Crassulaceae / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D010766:Phosphorylation; D018515:Plant Leaves / Q000737:chemistry; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013045:Species Specificity; D013997:Time Factors; D003313:Zea mays / Q000737:chemistry*
chemical_list: D004791:Enzyme Inhibitors; C069767:phosphoenolpyruvate carboxylase kinase; D017346:Protein Serine-Threonine Kinases; D002918:Chymotrypsin