title: Enzyme regulation in C4 photosynthesis: mechanism of activation of NADP-malate dehydrogenase by reduced thioredoxin.
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.
mesh_terms: D001426:Bacterial Proteins / Q000494:pharmacology*; D002846:Chromatography, Affinity; D003619:Dansyl Compounds; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D008291:Malate Dehydrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010788:Photosynthesis; D010944:Plants / Q000201:enzymology*; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013879:Thioredoxins / Q000494:pharmacology*; D003313:Zea mays
chemical_list: D001426:Bacterial Proteins; D003619:Dansyl Compounds; D013438:Sulfhydryl Compounds; D013879:Thioredoxins; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); C029038:dansyl chloride; D004229:Dithiothreitol