Ferredoxin thermophile

Sequence comparisons may also suggest new ligands. Recently, the complete amino acid sequence for a ferredoxin from the thermophilic organism Pyrococcus furiosus was determined (Eccleston et al., 1991). All... 

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. 

Aono S, Bentrop D, Bertini I, Donaire A, Luchinat C. Solution structure of the oxidized Fe7S8 ferredoxin from the thermophilic bacterium Bacillus schlegelii by H NMR spectroscopy. Biochemistry 1998 37 9812-26. 

The conversion of pyruvate to acetyl-CoA is catalysed by pyruvate oxidoreductase in the archaebacteria. The enzyme has been detected and characterised in Halobacterium halobium[i, 2i2 Tp. acidophilum, S. acidocaldarius and Desulfurococcus mobilis[i i], Pyrococcus furiosus [34] and in Methanobacterium thermoautotrophicum [35]. In the halophiles and thermophiles, ferredoxin serves as electron acceptor, whereas the methanogens use the deazaflavin derivative F420. 

Ma, K., Hutchins, A., Sung, S.J., and Adams, M.W. (1997) Pyruvate ferredoxin oxidoreductase from the hyper-thermophilic archaeon, Pyrococcus furiosus, functions as a CoA-dependent pyruvate decarboxylase. Proc. Nad. Acad. Sci. U.S.A., 94 (18), 9608-9613. 

For example, a ferredoxin hydrogenase (EC 1.12.7.2) has been isolated recently from the hyperthermophile Pyrococcus fUriosus [38]. The performance of this biocatalyst, which showed a remarkable stability under operative conditions, has been investigated for the NADPH regeneration in the reduction of prochiral ketones catalyzed by the thermophilic NADPH-dependent ADH from Thermoanaerohium sp. Total turnover numbers (TTNs mole product/mole consumed cofactor NADP" ") of 100 and 160 could be estimated in the reduction of acetophenone and (2S)-hydroxy-l-phenyl-propanone, respectively. As a side note, it should be mentioned that, although the activity of the P. furiosus hydrogenase increased exponentially with temperature up to its maximum above 80 °C, the reactions had to be performed at much lower temperature (40 °C) because of the thermal instability of NADPH. 

The importance of the ionic bonds in the thermostabilization was emphasized by Perutz (1978). From differences in rate of denaturation in mesophilic and thermophilic molecules, Perutz (1978) has evaluated the extrastabilization energy to be no more than 2 kcal/mole in ferredoxin and 5-10 kcal/mole in glyceraldehyde-3-phosphate dehydrogenase. Proteins from thermophilic organisms offer a very good example, allowing one to... 

---