Function of Two Dissimilar Thioredoxins in the Cyanobacterium, Anabaena sp. 7120
The activities of enzymes involved in carbon dioxide fixation in photosynthetic organisms are regulated by a variety of physiological factors such as substrate and effector levels, intracellular pH and ion concentration, and redox control (1). Redox control can be effected through NADP+/NADPH ratios, glutathione, or thioredoxin. Thioredoxin is a small disulfide-containing protein which has been implicated in the regulation of a number of processes in plant metabolism, including carbon dioxide fixation, sulfate metabolism, and deoxyribonucleotide synthesis. Two thioredoxin fractions occur in chloroplasts of higher plants which can modulate different enzymes although with some overlap of specificities. Thioredoxin in photosynthetic organisms can in turn be reduced by either ferredoxin or NADPH. Like higher plant chloroplasts, two dissimilar thioredoxins occur in the cyanobacterium, Anabaena sp. strain PCC 7120. The cyanobacteria provide a simple model system for investigating processes occurring in the chloroplast.
KeywordsPhotosynthetic Organism Ribonucleotide Reductase Spinach Chloroplast Sulfate Metabolism Carbon Dioxide Fixation
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