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Regulation of Plant Pyruvate Dehydrogenase Complex by Phosphorylation ¹

^a Department of Biochemistry, University of Missouri, Columbia, Missouri 65201

The ATP-dependent inactivation of the pyruvate dehydrogenase complex (PDC) was examined using ruptured mitochondria and partially purified pyruvate dehydrogenase complex isolated from broccoli and cauliflower (Brassica oleracea) bud mitochondria. The ATP-dependent inactivation was temperature- and pH-dependent. [³²P]ATP experiments show a specific transphosphorylation of the -PO₄ of ATP to the complex. The phosphate attached to the PDC was labile under mild alkaline but not under mild acidic conditions. The inactivated-phosphorylated PDC was not reactivated by 20 mM MgCl₂, dialysis, Sephadex G-25 treatment, apyrase action, or potato acid phosphatase action. However, partially purified bovine heart PDC phosphatase catalyzed the reactivation and dephosphorylation of the isolated plant PDC. The ATP-dependent inactivation-phosphorylation of the PDC was inhibited by pyruvate. It is concluded that the ATP-dependent inactivation-phosphorylation of broccoli and cauliflower mitochondrial PDC is catalyzed by a PDC kinase. It is further concluded that the PDC from broccoli and cauliflower mitochondria is capable of interconversion between an active (dephosphorylated) and an inactive (phosphorylated) form.