Plant and Cell Physiology Supplement
Supplement to Plant and Cell Physiology Vol. 47
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The cytosolic malate dehydrogenase in higher plants is a novel thiol enzyme
Satoshi HaraKen Motohashi*Toru Hisabori
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Pages 215

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Abstract
The cytosolic malate dehydrogenase (MDHcyt) was captured by thioredoxin affinity chromatography as a possible target protein for the cytosolic thioredoxin. We therefore examined whether MDHcyt can interact with thioredoxin and whether the activity is actually affected by the redox state of the enzyme. For this purpose, we expressed the recombinant MDHcyt in E. coli. When the recombinant protein was completely oxidized using CuCl2, the enzyme became inactive. Inactivation was easily recovered when the protein was incubated with low concentrations of DTT in the presence of thioredoxin. The redox regulation of MDHcyt was related to formation of the dimer. To clarify the critical cysteines, we prepared mutant MDHcyt in which one of six cysteine residues was substituted with serine, and studied their redox sensitivity. In addition, we determined the critical disulfide bond by way of peptide mapping analysis. These data clearly indicate that MDHcyt is a novel thiol enzyme.
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© 2006 by The Japanese Society of Plant Physiologists
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