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951.
Ormerod J 《Photosynthesis research》2003,76(1-3):135-143
Dogmas are unscientific. What is perhaps the greatest biological dogma of all time, the `unity of biochemistry' is, in the
main, still having its day. According to present knowledge, the exceptions to this dogma are mere details when seen in relation
to the biosystem as a whole. Nevertheless the exceptions are scientifically interesting and the understanding of them has
led to a better comprehension of photosynthesis and ecology. Until the discovery of 14C, photosynthetic CO2 fixation was like a slightly opened black box. With 14C in hand scientists mapped out the path of carbon in green plant photosynthesis in the course of a few years. The impressive
reductive pentose phosphate cycle was almost immediately assumed to be universal in autotrophs, including anoxygenic phototrophs,
in spite of the odd observation to the contrary. A new dogma was born and held the field for about two decades. Events began
to turn when green sulfur bacteria were found to contain ferredoxin-coupled ketoacid-oxidoreductases. This led to the formulation
of a novel CO2-fixing pathway, the reductive citric acid cycle, but its general acceptance required much work by many investigators. However,
the ice had now been broken and after some years a third mechanism of CO2 fixation was discovered, this time in Chloroflexus, and then a fourth in the same genus. One consequence of these discoveries is that it has become apparent that oxygen is an
important factor that determines the kind of CO2-fixing mechanism an organism uses. With the prospect of the characterization of hordes of novel bacteria forecast by molecular
ecologists we can expect further distinctive CO2 fixation mechanisms to turn up.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
952.
In the mid 1980s, it was observed that photosynthesis could still occur in the absence of the diffusible electron carrier
cytochrome c
2 in the purple non-sulfur facultative phototrophic bacterium Rhodobacter capsulatus. This serendipic finding led to the discovery of a novel class of membrane-anchored electron carrier cytochromes and their
associated electron transfer pathways. Studies of cytochrome c
y of R. capsulatus (and its homologues in other species) have modified the previous dogma of electron transfer between photosynthetic and respiratory
membrane protein complexes with a new paradigm, in which these proteins and their electron carriers can form `hard-wired'
structural super-complexes. Here, we reminisce on the early days of this discovery, its impacts on our understanding of cellular
energy transduction pathways and the physiological roles played by the electron carrier cytochromes c, and discuss the current knowledge and emerging future challenges of this field.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
953.
Albertsson PA 《Photosynthesis research》2003,76(1-3):217-225
The role of photosynthetic pigments in the development of separation methods in biochemistry during the period 1900-1980 is described beginning with M. Tswett who introduced separation of chlorophylls and carotenoids on columns and coined the term chromatography in 1906. In Uppsala, T. Svedberg developed the ultracentrifuge in the 1920s. A. Tiselius improved electrophoresis in the 1930s and developed chromatography of proteins in the 1940s and 1950s. Others of 'The Uppsala school in separation science' include J. Porath, P. Flodin and S. Hjertén who further developed various gel chromatographic methods. Hjertén introduced free zone electrophoresis in narrow tubes, a forerunner of capillary electrophoresis. Two proteins, phycoerythrin and phycocyanin, were used as test substances in all these methodological studies. Aqueous two-phase partitioning as a separation method was introduced in 1956 by the author. In this work, chloroplast particles were used, and the method was applied for the separation and purification of intact chloroplasts, inside-out thylakoid vesicles and plasma membranes. My research was carried out in cooperation with G. Blomquist, G. Johansson, C. Larsson, B. Andersson and H.-E. Akerlund during a 20-year period, 1960-1980. 相似文献
954.
955.
956.
Chung HS Shin CH Lee EJ Hong SH Kim HM 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,135(2):197-203
Using mouse peritoneal macrophages, we have examined the mechanism by which, Smilacis rhizoma (SR) regulates nitric oxide (NO) production. When SR was used in combination with recombinant interferon-gamma (rIFN-gamma), there was a marked cooperative induction of NO production. However, SR had no effect on NO production by itself. The increased production of NO from rIFN-gamma plus SR-stimulated cells was almost completely inhibited by pre-treatment with pyrrolidine dithiocarbamate (PDTC), an inhibitor of nuclear factor kappa B (NF-kappaB). Furthermore, treatment of peritoneal macrophages with rIFN-gamma plus SR caused a significant increase in tumor necrosis factor-alpha (TNF-alpha) production. PDTC also decreased the effect of SR on TNF-alpha production significantly. These findings demonstrate that SR increases the production of NO and TNF-alpha by rIFN-gamma-primed macrophages and suggest that NF-kappaB plays a critical role in mediating these effects of SR. 相似文献
957.
Kandzia R Stumpe M Berndt E Szalata M Matsui K Feussner I 《Journal of plant physiology》2003,160(7):803-809
Fatty acid hydroperoxide lyase (HPL) is a membrane associated P450 enzyme that cleaves fatty acid hydroperoxides into aldehydes and omega-oxo fatty acids. One of the major products of this reaction is (3Z)-hexenal. It is a constituent of many fresh smelling fruit aromas. For its biotechnological production and because of the lack of structural data on the HPL enzyme family, we investigated the mechanistic reasons for the substrate specificity of HPL by using various structural analogues of HPL substrates. To approach this 13-HPL from Arabidopsis thaliana was cloned and expressed in E. coli utilising a His-Tag expression vector. The fusion protein was purified by affinity chromatography from the E. coli membrane fractions and its pH optimum was detected to be pH 7.2. Then, HPL activity against the respective (9S)- and (13S)-hydroperoxides derived either from linoleic, alpha-linolenic or gamma-linolenic acid, respectively, as well as that against the corresponding methyl esters was analysed. Highest enzyme activity was observed with the (13S)-hydroperoxide of alpha-linolenic acid (13alpha-HPOT) followed by that with its methyl ester. Most interestingly, when the hydroperoxy isomers of gamma-linolenic acid were tested as substrates, 9gamma-HPOT and not 13gamma-HPOT was found to be a better substrate of the enzyme. Taken together from these studies on the substrate specificity it is concluded that At13HPL may not recognise the absolute position of the hydroperoxy group within the substrate, but shows highest activities against substrates with a (1Z4S,5E,7Z)-4-hydroperoxy-1,5,7-triene motif. Thus, At13HPL may not only be used for the production of C6-derived volatiles, but depending on the substrate may be further used for the production of Cg-derived volatiles as well. 相似文献
958.
Bonicalzi ME Vodenicharov M Coulombe M Gagné JP Poirier GG 《Biology of the cell / under the auspices of the European Cell Biology Organization》2003,95(9):635-644
Poly(ADP-ribosyl)ation is an important post-translational modification which mostly affects nuclear proteins. The major roles of poly(ADP-ribose) synthesis are assigned to DNA damage signalling during base excision repair, apoptosis and excitotoxicity. The transient nature and modulation of poly(ADP-ribose) levels depend mainly on the activity of poly(ADP-ribose) polymerase-1 (PARP-1) and poly(ADP-ribose) glycohydrolase (PARG), the key catabolic enzyme of poly(ADP-ribose). Given the fact that PARG substrate, poly(ADP-ribose), is found almost exclusively in the nucleus and that PARG is mainly localized in the cytoplasm, we wanted to have a closer look at PARG subcellular localization in order to better understand the mechanism by which PARG regulates intracellular poly(ADP-ribose) levels. We examined the subcellular distribution of PARG and of its two enzymatically active C-terminal apoptotic fragments both biochemically and by fluorescence microscopy. Green fluorescent protein (GFP) fusion proteins were constructed for PARG (GFP-PARG), its 74 kDa (GFP-74) and 85 kDa (GFP-85) apoptotic fragments and transiently expressed in COS-7 cells. Localization experiments reveal that all three fusion proteins localize predominantly to the cytoplasm and that a fraction also co-localizes with the Golgi marker FTCD. Moreover, leptomycin B, a drug that specifically inhibits nuclear export signal (NES)-dependent nuclear export, induces a redistribution of GFP-PARG from the cytoplasm to the nucleus and this nuclear accumulation is even more pronounced for the GFP-74 and GFP-85 apoptotic fragments. This observation confirms our hypothesis for the presence of important regions in the PARG sequence that would allow the protein to engage in CRM1-dependent nuclear export. Moreover, the altered nuclear import kinetics found for the apoptotic fragments highlights the importance of PARG N-terminal sequence in modulating PARG nucleocytoplasmic trafficking properties. 相似文献
959.
Baldin V Theis-Febvre N Benne C Froment C Cazales M Burlet-Schiltz O Ducommun B 《Biology of the cell / under the auspices of the European Cell Biology Organization》2003,95(8):547-554
Regulation of the intracellular localisation of its actors is one of the key mechanisms underlying cell cycle control. CDC25 phosphatases are activators of Cyclin-Dependent Kinases (CDK) that undergo nucleo-cytoplasmic shuttling during the cell cycle and in response to checkpoint activation. Here we report that the protein kinase PKB/Akt phosphorylates CDC25B on serine 353, resulting in a nuclear export-dependent cytoplasmic accumulation of the phosphatase. Oxidative stress activates PKB/Akt and reproduces the effect on CDC25B phosphorylation and localisation. However, inhibition of PKB/Akt activity only partially reverted the effect of oxidative stress on CDC25B localisation and mutation of serine 353 abolishes phosphorylation but only delays nuclear exclusion. These results indicate that additional mechanisms are also involved in preventing nuclear import of CDC25B. Our findings identify CDC25B as a target of PKB/Akt and provide new insight into the regulation of its localisation in response to stress-activated signalling pathways. 相似文献
960.
Ervatamia coronaria, a flowering plant (family Apocynaceae) indigenous to India, has medicinally important applications. A search for biochemical constituents of the latex of the plant yielded at least three thiol proteases with distinctly different properties. One of them, a highly active protease (ervatamin A), was purified to homogeneity by ion exchange and gel filtration chromatography. The enzyme exhibited high proteolytic activity toward natural substrates and amidolytic activity toward synthetic substrates. The pH and temperature optima for proteolytic activity were 8–8.5 and 50–55°C, respectively. Proteolytic activity of the enzyme was strongly inhibited by thiol-specific inhibitors. The estimated molecular mass of the enzyme was 27.6 kDa. The extinction coefficient (1% 280) of the enzyme was estimated as 21.9, and the protein molecule consists of 8 tryptophan, 11 tyrosine and 7 cysteine residues. Isoelectric point of the purified enzyme was 8.37. Polyclonal antibodies raised against the pure enzyme gave a single precipitin line in Ouchterlony's double immunodiffusion and a typical color in ELISA. The N-terminal sequence of the enzyme showed conserved amino acid residues to other plant cysteine proteases. Ervatamin A shows high activity in relation to the other thiol proteases isolated from the same source. 相似文献