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21.
We have used [2-13C]d-glucose and carbon-13 nuclear magnetic resonance (NMR) spectroscopy to investigate metabolic fluxes through the major pathways of glucose metabolism in intact human erythrocytes and to determine the interactions among these pathways under conditions that perturb metabolism. Using the method described, we have been able to measure fluxes through the pentose phosphate pathway, phosphofructokinase, the 2,3-diphosphoglycerate bypass, and phosphoglycerate kinase, as well as glucose uptake, concurrently and in a single experiment. We have measured these fluxes in normal human erythrocytes under the following conditions: (1) fully oxygenated; (2) treated with methylene blue; and (3) deoxygenated. This method makes it possible to monitor various metabolic effects of stresses in normal and pathological states. Not only has 13C-NMR spectroscopy proved to be a useful method for measuring in vivo flux through the pentose phosphate pathway, but it has also provided additional information about the cycling of metabolites through the non-oxidative portion of the pentose phosphate pathway. Our evidence from experiments with [1-13C]-, [2-13C]-, and [3-13C]d-glucoses indicates that there is an observable reverse flux of fructose 6-phosphate through the reactions catalyzed by transketolase and transaldolase, even in the presence of a net flux through the pentose phosphate pathway. 相似文献
22.
用闪光动力学光谱仪测量了酰化紫膜LB膜中M衰减速率的变化。酰化紫膜LB膜的衰减无论是悬浮液状态,还是LB膜中,均比未修饰的要慢。在温度为20℃时,酰化紫膜LB随着相对湿度的增加,M衰减加快。在相对湿度较低时(RH34—75%),变化较平缓,即M的衰减加快不明显;在相对湿度较高时(RH84—95%),M衰减明显加快。温度的变化则随相对湿度不同而不同。相对湿度较低时,随着温度的升高,M衰减加快;相对湿度较高时,M衰减反而减慢。酰化紫膜悬浮液的M衰减随着温度的升高而明显加快.这说明酰化紫膜LB膜中BR水合程度可能是直接影响M衰减的因素之一。 相似文献
23.
24.
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
25.
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
26.
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
27.
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
28.
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
29.
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
30.
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