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1.
Summary. Both 1,4-benzoquinones and 1,4-naphthoquinones were attached to the non-proteinogenic amino acid taurine to form N-quinonyl
taurine derivatives. The products were formed via the direct Michael-like addition or by substitution of a good leaving group.
An attempt to bridge the two moieties via an ureido spacer resulted in the formation of a bis-quinonylamino isocyanurate derivative.
Preliminary MO calculations provided internal ground-state geometries and orbital coefficients of the HOMO levels in two representing
taurine conjugates.
Received May 6, 2002 Accepted August 13, 2002 Published online December 18, 2002
Acknowledgments This research was supported by the Israel Science Foundation founded by the Academy of Science and Humanities. We wish to
thank Ms. Ethel Solomon for skilled technical help.
Authors' address: Prof. Shmuel Bittner, Department of Chemistry, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel,
Fax: (972)-8-6472943, E-mail: bittner@bgumail.bgu.ac.il 相似文献
2.
Th. Bittner J. Voigt G. Kehrberg H. -J. Eckert G. Renger 《Photosynthesis research》1991,28(3):131-139
Utilizing a two-beam technique in the frequency domain, the pumped absorption of PS II membrane fragments from spinach and of acetonic chlorophyll-a solutions was measured at room temperature. In a very narrow wavelength region (0.2 nm around the pump pulse wavelength) the relative test beam transmission exhibited either a decrease or an increase, respectively, dependent on the intensity of a strong pump beam. In contrast, the transmission changes of chl-a solutions were not affected by the wavelength mistuning between pump and test beam. The data obtained for PS II membrane fragments were interpreted in terms of excited state absorption of pigment-protein clusters within the light-harvesting complex of PS II. The interpretation of the small absorption band as a homogeneously broadened line led to a transversal relaxation time for chlorophyll in vivo of about 1 ps.Abbreviations PS I
photosystem I of green plants
- PS II
photosystem II of green plants
- P700
primary donor of PS I
- P680
primary donor of PS II 相似文献
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Induction of apoplastic invertase of Chenopodium rubrum by D-glucose and a glucose analog and tissue-specific expression suggest a role in sink-source regulation. 总被引:9,自引:6,他引:3 下载免费PDF全文
Photoautotrophic suspension-culture cells of Chenopodium rubrum that were shifted to mixotrophic growth by adding glucose were used as model system to investigate the influence of the source-sink transition in higher plants on the expression and enzyme activities of intracellular and extracellular invertases. The complete cDNA coding for an extracellular invertase was cloned and sequenced from C. rubrum, and its identity has been proven by heterologous expression in Saccharomyces cerevisiae. The higher activity of extracellular invertase after preincubation in the presence of glucose was paralleled by an increased expression of the corresponding gene. The induction by glucose could be mimicked by the nonmetabolizable glucose analog 6-deoxyglucose. Both enzyme activity and mRNA level of extracellular invertase showed a sink-tissue-specific distribution in plants. The activity of neutral and acidic intracellular invertases were not affected by preincubation of autotrophic tissue cultures with sugars, nor did they show a tissue-specific distribution in plants. The data suggest that apoplastic invertase not only has an important function in phloem unloading and carbohydrate partitioning between source and sink tissues but may also have a role in establishing metabolic sinks. 相似文献
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Membrane potential and input resistance are ambiguous measures of sealing of transected cable-like structures. 总被引:1,自引:0,他引:1 下载免费PDF全文
For many years, membrane potential (Vm) and input resistance have been used to characterize the electrophysiological nature of a seal (barrier) that forms at the cut end of a transected axon or other extended cytoplasmic structure. Data from a mathematical and an analog model of a transected axon and other theoretical considerations show that steady-state values of Vm and input resistance measured from any cable-like structure provide a very equivocal assessment of the electrical barrier (seal) at the cut end. Extracellular assessments of injury currents almost certainly provide a better electrophysiological measure of the status of plasma membrane sealing because measurements of these currents do not depend on the cable properties of extended cytoplasmic processes after transection. 相似文献
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Calcium-activated potassium conductance in presynaptic terminals at the crayfish neuromuscular junction 下载免费PDF全文
Membrane potential changes that typically evoke transmitter release were studied by recording intracellularly from the excitor axon near presynaptic terminals of the crayfish opener neuromuscular junction. Depolarization of the presynaptic terminal with intracellular current pulses activated a conductance that caused a decrease in depolarization during the constant current pulse. This conductance was identified as a calcium-activated potassium conductance, gK(Ca), by its disappearance in a zero-calcium/EGTA medium and its block by cadmium, barium, tetraethylammonium ions, and charybdotoxin. In addition to gK(Ca), a delayed rectifier potassium conductance (gK) is present in or near the presynaptic terminal. Both these potassium conductances are involved in the repolarization of the membrane during a presynaptic action potential. 相似文献
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