Regulation of Plant Enzymes

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This is a 4 year research program to elucidate the mechanism of regulation of enzymes controlling photosynthesis. One pivotal mechanism is the cytosolic fructose-2,6-bisphosphate system that regulates sucrose synthesis and breakdown in leaves. The objectives are to: (1) purify and characterize at the protein and gene levels newly identified leaf enzymes that synthesize and degrade fructose-2,6-bisphosphate; (2) determine whether these same activities of nonphotosynthetic (sink) tissues containing amyloplasts reside on enzymes similar to those of leaves. In parallel, studies will be continued on the chloroplast ferredoxin-thioredoxin system, a protein-mediated mechanism that links light to the regulation of enzymes functional in photosynthesis and related processes. These studies will (1) deduce the importance of catalytically active thiols in the photoregulation of target enzymes in isolated chloroplasts and leaves, and (2) characterize the remaining poorly understood component of this system--the novel enzyme ferredoxin-thioredoxin reductase (FTR)--with respect to mechanism of action, crystal structure, and EPR/redox properties. This research will increase our understanding of how plants synthesize and store starch and sucrose, the major reservoirs of edible carbohydrate.***