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21.
22.
Stefan Falk Guy Samson Doug Bruce Norman P. A. Huner David E. Laudenbach 《Photosynthesis research》1995,45(1):51-60
Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43, which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43 apoprotein (designated isiA
–) and (ii) flavodoxin (designated isiB
–). The function of CP 43 was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA
– and isiB
– strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43 and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crossection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43 is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB
– strain grown under iron-deficient conditions, CP 43 was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (Fo) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.Abbreviations Chl
chlorophyll
- CP 43, CP 47 and CP 43
Chl a binding protein complexes of indicated molecular mass
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- Fm and Fm
fluorescence when all PS II reaction centers are dosed in dark- and light-acclimated cells, respectively
- Fo
fluorescence when all PS II reaction centers are open in dark acclimated cells
- Fv
variable fluorescence after dark acclimation (Fm–Fo) 相似文献
23.
Direct sequence analysis of proteins by in-source fragmentation during delayed ion extraction. 总被引:1,自引:1,他引:0 下载免费PDF全文
J. J. Lennon K. A. Walsh 《Protein science : a publication of the Protein Society》1997,6(11):2446-2453
Continuous segments of amino acid sequence information as long as 41 residues have been deduced by interpretation of matrix-assisted laser desorption/ionization-generated ion signals dominated by Cn fragmentation within the ion source of a linear time-of-flight mass spectrometer utilizing delayed ion extraction. The technique has been applied successively to five proteins of mass 12.2 kDa to 18.3 kDa, yielding segments of continuous sequence as long as 41 residues without the need for prior proteolytic fragmentation. Intact crosslinks such as disulfides or heme linkages interrupt the generation of these data. 相似文献
24.
Whitening of Gracilaria chilensis, accompanied by tissue softening and thallus fragmentation, was found to be associated with the presence of an endophytic
amoeba. Although the symptoms developed originally in green mutant thalli, subsequent infections in the laboratory also affected
normal, wild-type G. chilensis. Ultrastructural evidence indicates that the amoebae perforate the host cell walls of both cortical and medullary cells and
digest their protoplasm. Feeding by the amoeba appears to involve both phagocytosis and enzymatic digestion of the host tissue.
Destruction of the host tissue resulted in large cavities first, followed by thallus fragmentation. No other organism was
found during the early stages of thallus invasion by the amoeba, although bacteria may appear once the amoeba reaches the
inner tissues of the host. 相似文献
25.
Radical-pair decay kinetics and molecular triplet quantum yields at various magnetic fields are reported for quinone-depleted reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides R26. The radical-pair decay is observed by picosecond absorption spectroscopy to be a single exponential to within the experimental uncertainty at all fields. The decay time increases from 13 ns at zero field to 17 ns at 1 kG, and decreases to 9 ns at 50 kG. The orientation averaged quantum yield of formation of the molecular triplet of the primary electron donor, 3P, drops to 47% of its zero-field value at 1 kG and rises to 126% at 50 kG. Combined analysis of these data gives a singlet radical-pair decay rate constant of 5 · 107s?1, a lower limit for the triplet radical-pair decay rate constant of 1 · 108s?1 and a lower limit for the quantum yield of radical-pair decay by the triplet channel of 38% at zero field. The upper limit of the quantum yield of 3P formation at zero field is measured to be 32%. In order to explain this apparent discrepancy, decay of the radical pair by the triplet channel must lead to some rapid ground state formation as well as some 3P formation. It is proposed that the triplet radical pair decays to a triplet charge-transfer state which is strongly coupled to the ground state by spin-orbit interactions. Several possibilities for this charge-transfer state are discussed. 相似文献
26.
The phase behavior of isolated photoreceptor membrane lipids is further investigated by 31P-NMR, in view of earlier discrepant results [(1979) Biochim. Biophys. Acta 558, 330–337; (1982) FEBS Lett. 124, 93–99]. We present evidence that the discrepancy is due to bivalent cations. When resuspended in aqueous media at neutral pH in the absence of bivalent cations, the isolated photoreceptor membrane lipids largely adopt the bilayer configuration. However, upon addition of such cations (Ca2+ Mg2+) or when resuspended in their presence, the formation of other phases (hexagonal HII, lipidic particles) results. The rate of this transition depends on cation concentration and temperature. The transition is not easily reversed by addition of EDTA. Implications with regard to photoreceptor membrane structure and function need further study. 相似文献
27.
Abstract The time course of photobleaching and the nanosecond fluorescence decay have been measured from microscopic samples of methanogenic bacteria, to our knowledge the first application of these methods in this field. Decay times of about 1 ns and 3 ns were obtained for the specific coenzymes F420 and 7-methylpterin, respectively. In contrast to methylpterin and other fluorescent compounds the intensity of F420 fluorescence was reduced selectively due to photobleaching. This effect, as well as the different decay time constants could be used to discriminate F420 from other fluorescent components. In addition, active and inactive bacterial cells could be differentiated following the course of photobleaching. 相似文献
28.
T. K. Kirk E. Schultz W. J. Connors L. F. Lorenz J. G. Zeikus 《Archives of microbiology》1978,117(3):277-285
Culture parameters influencing metabolism of synthetic14C-lignins to14CO2 in defined media have been studied in shallow batch cultures of the ligninolytic wood-destroying HymenomycetePhanerochaete chrysosporium Burds. Study of the effect of O2 concentration in the gas phase above non-agitated cultures indicated essentially complete absence of attack on the lignin polymer at 5% O2 in N2, and a 2- to 3-fold enhancement by 100% O2 as compared to air (21% O2). Agitation of the cultures resulting in the formation of mycelial pellets greatly suppressed lignin decomposition. The optimum culture pH for lignin decomposition was 4 to 4.5, with marked suppression above 5.5 and below 3.5. The source of nutrient nitrogen (NO
3
–
, NH
4
+
, amino acids) had little influence on lignin decomposition, but the concentration of nitrogen was critical; decomposition at 24 mM was only 25–35% of that at 2.4 mM N. Thiamine was the only vitamin required for growth and lignin decomposition. Under the optimum conditions developed, decomposition of 5 mg of synthetic lignin was accompanied by utilization of approximately 100 mg of glucose. The influence of the various culture parameters was analogous for metabolism of synthetic lignin labeled in the ring-,side chain-, and methoxyl carbon atoms. 相似文献
29.
We report fluorescence lifetimes for in vivo chlorophyll a using a time-correlated single-photon counting technique with tunable dye laser excitation. The fluorescence decay of dark-adapted chlorella is almost exponential with a lifetime of 490 ps, which is independent of excitation from 570 nm to 640 nm.Chloroplasts show a two-component decay of 410 ps and approximately 1.4 ns, the proportion of long component depending upon the fluorescence state of the chloroplasts. The fluorescence lifetime of Photosystem I was determined to be 110 ps from measurements on fragments enriched in Photosystem I prepared from chloroplasts with digitonin. 相似文献
30.
Previous research showed that addition of nutrient nitrogen to ligninolytic (stationary, nitrogen-starved) cultures of the wood-decomposing basidiomycete Phanerochaete chrysosporium causes a suppression of lignin degradation. The present study examined early effects on nitrogen metabolism that followed addition of NH
4
+
and l-glutamate at concentrations that yield similar patterns of suppression. Both nitrogenous compounds were rapidly assimilated (>80% in 6 h). Both caused an initial 80% or greater increase in the intracellular glutamate pool and had similar effects in increasing the specific activities of NADP- and NAD-glutamate dehydrogenases and glutamine synthetase. Differences between the effects of added NH
4
+
and glutamate showed that suppression was not correlated with intracellular pools of arginine or glutamine, nor was the maintenance of an elevated glutamate pool required to maintain the suppressed state. While a portion of the initial glutamate suppression could be attributed to an effect on central carbon metabolism through glutamate catabolism by NAD-glutamate dehydrogenase, the long term suppression by glutamate and the suppression by NH
4
+
were more specific. Suppression by NH
4
+
or glutamate in the presence or absence of protein synthesis (cycloheximide) followed essentially identical kinetics during 12 h. These results indicate that nitrogen additions cause a biochemical repression of enzymes associated with lignin degradation. Results are consistent with the hypothesis that nitrogen metabolism via glutamate plays a role in initiation of repression.Non-Standard Abbreviations DMS
2,2-dimethylsuccinate
- TCA
trichloroacetic acid 相似文献