Plant Physiology 100:908-914 (1992)
© 1992 American Society of Plant Biologists
Metabolism and Enzymology
Light Regulation of Leaf Mitochondrial Pyruvate Dehydrogenase Complex 1
Role of Photorespiratory Carbon Metabolism
Joanna Gemel and
Douglas D. Randall
Department of Biochemistry, University of Missouri, Columbia, Missouri 65211
Light-dependent inactivation of mitochondrial pyruvate dehydrogenase complex (mtPDC) in pea (Pisum sativum L.) leaves was further characterized, and this phenomenon was extended to several monocot and dicot species. The light-dependent inactivation of mtPDC in vivo was rapidly reversed in the dark, even after prolonged illumination. The mtPDC can be efficiently cycled through the inactivated-reactivated status by rapid light-dark cycling. Light-dependent inactivation of mtPDC was shown to be suppressed by inhibitors of photorespiratory carbon metabolism, including 2-pyridylhydroxymethane sulfonate, isonicotinic acid hydrazide, and aminoacetonitrile, and by an inhibitor of photosynthesis, 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Glycine fed to pea leaf strips in the dark yielded partially inactivated leaf mtPDC, and this inactivation was blocked by inhibitors of glycine oxidation. It is concluded that the photorespiratory glycine to serine conversion that occurs in C3 leaf mitochondria can provide the NADH to drive oxidative phosphorylation and subsequent inactivation of mtPDC. Glycine oxidation also produces ammonium ion, which has been shown to enhance the inactivation of mtPDC in vitro by stimulating the pyruvate dehydrogenase kinase that catalyzes the phosphorylation (inactivation) of the mtPDC. Thus, light-dependent, photorespiration-stimulated inactivation of the mtPDC can regulate carbon entry into the Krebs cycle during C3 photosynthesis.
1 This research was supported by the Missouri Agricultural Experiment Station and National Science Foundation grant No. IBN-9201292. This is journal No. 11,613 of the Missouri Agricultural Experiment Station. J.G. is the recipient of a Food for the 21st Century Program Visiting Scientist Fellowship.
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