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  • 1
    ISSN: 1432-072X
    Keywords: Photosynthesis ; Regulation ; Thioredoxin ; Cyanobacterium ; Chromatium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Enzymes that are regulated by the ferredoxin/thioredoxin system in chloroplasts — fructose-1,6-bisphosphatase (FBPase), sedoheptulose-1,7-bisphosphatase purified from two different types of photosynthetic prokaryotes (cyanobacteria, purple sulfur bacteria) and tested for a response to thioredoxins. Each of the enzymes from the cyanobacterium Nostoc muscorum, an oxygenic organism known to contain the ferredoxin/thioredoxin system, was activated by thioredoxins that had been reduced either chemically by dithiothreitol or photochemically by reduced ferredoxin and ferredoxin-thioredoxin reductase. Like their chloroplast counterparts, N. muscorum FBPase and SBPase were activated preferentially by reduced thioredoxin f. SBPase was also partially activated by thioredoxin m. PRK, which was present in two regulatory forms in N. muscorum, was activated similarly by thioredoxins f and m. Despite sharing the capacity for regulation by thioredoxins, the cyanobacterial FBPase and SBPase target enzymes differed antigenically from their chloroplast counterparts. The corresponding enzymes from Chromatium vinosum, an anoxygenic photosynthetic purple bacterium found recently to contain the NADP/thioredoxin sytem, differed from both those of cyanobacteria and chloroplasts in showing no response to reduced thioredoxin. Instead, C. vinosum FBPase, SBPase, and PRK activities were regulated by a metabolite effector, 5′-AMP. The evidence is in accord with the conclusion that thioredoxins function in regulating the reductive pentose phosphate cycle in oxygenic prokaryotes (cyanobacteria) that contain the ferredoxin/thioredoxin system, but not in anoxygenic prokaryotes (photosynthetic purple bacteria) that contain the NADP/thioredoxin system. In organisms of the latter type, enzyme effectors seem to play a dominant role in regulating photosynthetic carbon dioxide assimilation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Thioredoxin ; Cyanobacterium ; Ferredoxin ; Nostoc ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cell-free preparations of the cyanobacterium (bluegreen alga) Nostoc muscorum were assayed for thioredoxins and enzymes catalyzing the ferredoxin and NADP-linked reduction of thioredoxin. Nostoc was found to have two different thioredoxins: one of approximate molecular weight 16,000 (designated Nostoc thioredoxin f) that selectively activated chloroplast fructose 1,6-bisphosphatase, and another of approximate molecular weight 9,000 (designated Nostoc thioredoxin m) that selcetively activated chloroplast NADP-malate dehydrogenase. The two thioredoxins could be reduced either chemically with dithiothreitol or photochemically with ferredoxin and ferredoxin-thioredoxin reductase which, like the recently found regulatory iron-sulfur protein ferralterin, was present in Nostoc cells. Nostoc ferredoxin-thioredoxin reductase appeared to be similar to its chloroplast counterpart in enzyme specificity, molecular weight, and spectral properties. The Nostoc and spinach chloroplast ferredoxin-thioredoxin reductases as well as their thioredoxins, ferredoxins, and chlorophyll containing membranes were interchangeable in activating chloroplast fructose 1,6-bisphosphatase and NADP-malate dehydrogenase. There was no evidence for an NADP-linked thioredoxin reductase such as that of E. coli. The results are in accord with the conclusion that the cyanobacteria resemble higher plants in having a functional ferredoxin/thioredoxin system rather than an NADP/thioredoxin system typical of other bacteria.
    Type of Medium: Electronic Resource
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