Enzyme regulation in C4 photosynthesis: Mechanism of activation of NADP-malate dehydrogenase by reduced thioredoxin |
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Authors: | Jean-Pierre Jacquot Pierre Gadal Ann N. Nishizawa Boihon C. Yee Nancy A. Crawford Bob B. Buchanan |
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Affiliation: | 1. Laboratoire de Physiologie Végétale Métabolique, ERA CNRS 799 Université de Paris-Sud Bat. 430, 91405 Orsay-Cedex, France;2. Division of Molecular Plant Biology, Hilgard Hall, University of California, Berkeley, California 94720 USA |
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Abstract: | The mechanism of activation of thioredoxin-linked NADP-malate dehydrogenase was investigated by using 14C-iodoacetate and 14C-dansylated thioredoxin m, and Sepharose affinity columns (thioredoxin m, NADP-malate dehydrogenase) as probes to monitor enzyme sulfhydryl status and enzyme-thioredoxin interaction. The data indicate that NADP-malate dehydrogenase, purified to homogeneity from corn leaves, is activated by a net transfer of reducing equivalents from thioredoxin m, reduced by dithiothreitol, to enzyme disulfide groups, thereby yielding oxidized thioredoxin m and reduced enzyme. The appearance of new sulfhydryl groups that accompanies the activation of NADP-malate dehydrogenase appears to involve a structural change that is independent of the formation of a stable complex between the enzyme and reduced thioredoxin m. The data are consistent with the conclusion that oxygen promotes deactivation of NADP-malate dehydrogenase through oxidation of SH groups on reduced thioredoxin and on the reduced (activated) enzyme. |
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Keywords: | To whom correspondence should be addressed. |
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