Ferredoxin thioredoxin system

A relatively simple and quick procedure for the isolation of Photosystem I-enriched particles from the thermophilic cyanobacterium Phormidium laminosum, without the use of detergents for solubilization, is described. The procedure involves sonication of cells, centrifugation and DEAE-cellulose chromatography. The particles had an 02 uptake activity of up to 200 pmol 02. mg chlorophyll h 1 and appeared as vesicles of 200 100 nm diameter when observed under electron microscopy. The analysis of the chlorophyll-protein complexes by polyacrylamide gel electrophoresis showed that these particles are enriched in the complexes associated with Photosystem I and partially depleted in those associated with Photosystem II. The particles did not contain ferredoxin and were active in NADP-photoreduction only in the presence of added ferredox in. They were also able to photoreduce externally added electron mediators using ascorbate as electron donor, the reduced mediators can be coupled to hydrogenase for the production of H2 or for the activation of cyanobacterial phosphoribulokinase using a ferredoxin/thioredoxin system. 

Fig. 4. Enzymes regulated by the ferredoxin/thioredoxin system. The role of an FTR S-S group in the reduction of thioredoxins is based on unpublished findings of Droux, Miginiac-Maslow, Jacquot, Gadal and Buchanan. The role of thioredoxins in regulating phosphoglycerate kinase of C4 mesophyll cells is not indicated.

Another mechanism of light-dependent enzyme activation has been proposed in which a membrane-bound dithiol-containing factor (light-effect mediator or LEM) reduced by the photosynthetic electron transport system reductively activates regulated enzymes in the chloroplast [28]. Certain facets of this mechanism may be identical to the ferredoxin/thioredoxin system while other aspects are still the subject of debate [18,33],... 

In summary, current evidence [39-41] is thus consistent with the view that the ferredoxin/thioredoxin system functions in photosynthetically diverse types of plants as a master switch to restrict the activity of degradatory enzymes and activate biosynthetic enzymes in the light. It is significant that enzymes controlled by the ferredoxin/thioredoxin system (FBPase, SBPase, NADP-G3PDH, and PRK) function in the regenerative phase of the reductive pentose phosphate cycle that is needed to sustain its continued operation - i.e, to regenerate the carbon dioxide acceptor, Rbu-1,5-P2, from newly formed 3-PGA. It seems likely that one of these thioredoxin-linked enzymes limits the regeneration of Rbu-1,5-P2. 

Both potato tuber and potato leaf ADP-Glc PPases are plas-tidic the leaf enzyme is in the chloroplast, and the tuber enzyme is in the amyloplast (74). The ferredoxin-thioredoxin system is located in the chloroplast and thus, with photosynthesis, reduced thioredoxin is formed and activated within the leaf ADP-Glc PPase. At night, oxidized thioredoxin is formed it oxidizes and inactivates the ADP-Glc PPase. This activation/inactivation process during the light/dark cycle allows a fine tuning and dynamic regulation of starch synthesis in the chloroplasts. Thioredoxin isoforms are present in many different subcellular locations of plant tissues cytosol, mitochondria, chloroplasts, and even nuclei (75) and are also present in amyloplasts (76). 

Evolution of Oxygen by an Aquatic Plant Light is the principal regulator of photosynthesis. Light affects the activities of regulatory enzymes in photosynthetic processes by indirect mechanisms, which include changes in pH, Mg2+ concentration, the ferredoxin-thioredoxin system, and phytochrome. 

The ferredoxin-thioredoxin system. Thioredoxins are small proteins that transfer electrons from reduced ferredoxin to certain enzymes (Figure 13.17). (Recall that ferredoxin is an electron donor in PSI.) When exposed to light, PSI reduces ferredoxin, which then reduces ferredoxin-thioredoxin reductase (FTR),... 

Buchanan, B. B. 1991. Regulation of CO2 assimilation in oxygenic photosynthesis the ferredoxin/thioredoxin system. Perspective on its discovery, present status, and future development. Arch. Biochem. Biophys. 288 1 9. 

Light-induced control via the ferredoxin/ thioredoxin system, Rubisco is activated by CO2 (Chapter 13) and by fructose 6-P and is inhibited by fructose 1,6-P2 (Fig. 23-36), whose accumulation is a signal to turn off the carboxylase. Conversely, fructose... 

PRIMARY STRUCTURES OF REGULATORY PROTEINS FERREDOXIN-THIOREDOXIN SYSTEM OF SPINACH CHLOROPLASTS. 

Is the ferredoxin-thioredoxin system of Chlamydomonas effected by heterotrophic conditions To investigate the relationship between growth conditions and thioredoxins we examined the thioredoxins of Chlamydomonas under light and dark growth in both the wild type and the y-1 mutant. Chlamydomonas y-1 differs from the wild type in that it requires light to green. 

In chloroplasts of higher plants the ferredoxin-thioredoxin system links light-triggered events in thylakoid membranes with the regulation of enzymes in the stroma (1,2). If the conformation of enzymes changes because of modulators action then the surface exposed to the solvent will be different from the native state (3). As a consequence, interactions of modified enzymes with supramolecular structures (membranes, protein complexes) will differ respect to native forms. Since thylakoid membranes are complex structures they are not adequate for uncovering molecular mechanisms that participate in protein interactions(4). In thfe respect, the well-defined structure of micelles of non-ionic detergents constitute model compounds for the analysis of hydrophobic interactions in proteins (5,6). We report herein that chloroplast fructose-1,6-bisphosphatase interacts with micelles of Triton X-114 in a pH-dependent process. 

FBPase undergoes a reductive activation by accepting electrons from ferredoxin through the ferredoxin-thioredoxin system, which works as a link between the photosynthetic electron transport and enzyme regulation (7). The existence of non-covalent interactions of FBPase with the chloroplast membrane could improve the efficiency of its reductive light-activation. In this context the strong FBPase-thioredoxin interaction (8), the association between ferredoxin, thioredoxin and ferredoxin-thioredoxin reductase (9), the binding of ferredoxin to thylakoid membranes (10), and the existence of membrane-bound thioredoxins (11) may be relevant. 

Primary Structures of Regulatory Proteins of the Ferredoxin-Thioredoxin System of Spinach Chloroplasts 167... 

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