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11.
Shaltiel Shmuel Schvartz Iris Korc-Grodzicki Beatriz Kreizman Tamar 《Molecular and cellular biochemistry》1993,127(1):283-291
In addition to itsintra-cellular functions, cAMP-dependent protein kinase (PKA) may well have anextra-cellular regulatory role in blood. This suggestion is based on the following experimental findings: (a) Physiological stimulation of blood platelets brings about a specific release of PKA, together with its co-substrates ATP and Mg++; (b) In human serum, an endogenous phosphorylation of one protein (p75, Mr 75 kDa) occurs; this phosphorylation is enhanced by addition of cAMP and blocked by the Walsh-Krebs specific PKA inhibitor; (c) No endogenous phosphorylation of p75 occurs in human plasma devoid of platelets, but the selective labeling of p75 can be reproduced by adding to plasma the pure catalytic subunit of PKA; (d) p75 was shown to be vitronectin (V), a multifunctional protein implicated in processes associated with platelet activation, and thus a protein whose function may require modulation for control; (e) The phosphorylation of vitronectin occurs at one site (Ser378) which, at physiological pH, is buried in its two-chain form (V65+10) but becomes exposed in the presence of glycosaminoglycans (GAGs) e.g. heparin or heparan sulfate. Such a transconformation may be used for targeting the PKA phosphorylation to vitronectin molecules bound to GAGs, for example in the extracellular matrix or on cell surfaces; (f) From the biochemical point of view (Km values and physiological concentrations) the phosphorylation of vitronectin can take place at the locus of a hemostatic event; (g) The phosphorylation of Ser378 in vitronectin alters its function, since it significantly reduces its ability to bind the inhibitor-1 of plasminogen activator(s) (PAI-1). Physiologically, this functional modulation may be involved in unleashing PAI-1, allowing its translocation to control the inhibitory function of PAI-1 and, through it, regulating the conversion of plasminogen to active plasmin.Dedicated to Edmond H. Fischer and Edwin G. Krebs, with gratitude for teaching us the right measure of thoroughness and vision in research. 相似文献
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The photochemical activities and fluorescence properties of cells, spheroplasts and spheroplast particles from the blue-green alga Phormidium luridum were compared. The photochemical activities were measured in a whole range of wavelengths and expressed as quantum yield spectra (quantum yield vs. wavelength). The following reactions were measured: Photosynthesis (O2 evolution) in whole cells; Hill reaction (O2 evolution) with Fe(CN)63? and NADP as electron acceptors (Photosystem II and Photosystem II+Photosystem I reactions); electron transfer from reduced 2,6-dichlorophenolindophenol to diquat (Photosystem I reaction). The fluorescence properties were emission spectra, quantum yield spectra and the induction pattern.On the basis of comparison between the quantum yield spectra and the pigments compositions the relative contribution of each pigment to each photosystem was estimated. In normal cells and spheroplasts it was found that Photosystem I (Photosystem II) contains about 90 % (10 %) of the chlorophyll a, 90 % (10 %) of the carotenoids and 15 % (85 %) of the phycocyanin. In spheroplast particles there is a reorganization of the pigments: they loose a certain fraction (about half) of the phycocyanin but the remaining phycocyanin attaches itself exclusively to Photosystem I (!). This is reflected by the loss of Photosystem II activity, a flat quantum yield vs. wavelength dependence and a loss of the fluorescence induction.The fluorescence quantum yield spectra conform qualitatively to the above conclusion. More quantitative estimation shows that only a fraction (20–40 %) of the chlorophyll of Photosystem II is fluorescent. Total emission spectrum and the ratio of variable to constant fluorescence are in agreement with this conclusion.The fluorescence emission spectrum shows characteristic differences between the constant and variable components. The variable fluorescence comes exclusively from chlorophyll a; the constant fluorescence is contributed, in addition to chlorophyll a, by phycocyanine and an unidentified long wavelength component.The variable fluorescence does not change in the transition from whole cells to spheroplasts. However, the constant fluorescence increases considerably. This indicates the release of a small fraction of pigments from the photosynthetic photochemical apparatus which then become fluorescent. 相似文献
13.
Spatial and temporal electroselection patterns in electric field stimulation of polarized luminescence from photosynthetic membrane vesicles 总被引:1,自引:1,他引:0
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Yosef Rosemberg Philip Rozen Shmuel Malkin Rafi Korenstein 《Biophysical journal》1992,61(6):1585-1594
Electroselection processes of charge recombination are manifested in the study of electric field induced polarized emission from photosynthetic membrane vesicles. The study explores the coupled spatial-temporal characteristics of electric field induced charge recombination by examining the dependence of the integrated polarized emission and the time dependent polarization on electric field strength. The experimental results were fitted to theoretical models by computer simulations employing empirical parameters. Simulation of the dependence of the integrated polarized components of emission on electric field strength, suggests field-dependent increased ratio between radiative and nonradiative rates of charge recombination. The observation that the initial polarization values are independent of electric field strength supports the assumption that electric field induced emission originates from the pole area and then spreads away from it towards the equator. The propagation rate of this electric field induced charge recombination from the pole area towards the equator is reflected by the decay of polarization which increases upon raising the electric field strength. Simulation of the polarization's decay, based on a calculated angle of 26.3 ± 0.4° between the transition moment of emission and the plane of the membrane, establishes coupled temporal spatial patterns of electroselection in intramembrane electron transfer invoked by exposing preilluminated photosynthetic vesicles to a homogeneous electric field. 相似文献
14.
Summary DNA synthesis in a thymine-requiring Escherichia coli K12 strain was studied by exploiting deoxyguanosine, so simulating the behaviour of Thy+ strains. DNA synthesis is inhibited during the first 25 min after a nutritional shift-up. The new DNA/mass is lower than that predicted by current models for initiation control.Dedicated to the memory of Shmuel Zabrovitz, whose high spirits and good humor enabled him to complete the work while struggling with his lethal diseaseDeceased 相似文献
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Archana Jha Malini Ahuja József Maléth Claudia M. Moreno Joseph P. Yuan Min Seuk Kim Shmuel Muallem 《The Journal of cell biology》2013,202(1):71-79
Ca2+ influx by store-operated Ca2+ channels (SOCs) mediates all Ca2+-dependent cell functions, but excess Ca2+ influx is highly toxic. The molecular components of SOC are the pore-forming Orai1 channel and the endoplasmic reticulum Ca2+ sensor STIM1. Slow Ca2+-dependent inactivation (SCDI) of Orai1 guards against cell damage, but its molecular mechanism is unknown. Here, we used homology modeling to identify a conserved STIM1(448–530) C-terminal inhibitory domain (CTID), whose deletion resulted in spontaneous clustering of STIM1 and full activation of Orai1 in the absence of store depletion. CTID regulated SCDI by determining access to and interaction of the STIM1 inhibitor SARAF with STIM1 Orai1 activation region (SOAR), the STIM1 domain that activates Orai1. CTID had two lobes, STIM1(448–490) and STIM1(490–530), with distinct roles in mediating access of SARAF to SOAR. The STIM1(448–490) lobe restricted, whereas the STIM1(490–530) lobe directed, SARAF to SOAR. The two lobes cooperated to determine the features of SCDI. These findings highlight the central role of STIM1 in SCDI and provide a molecular mechanism for SCDI of Orai1. 相似文献
20.
Yoav Gazit Sagi Gavriel Ruti Akiva Doron Timar 《Entomologia Experimentalis et Applicata》2013,147(2):120-125
GF‐120, a fruit fly bait designed to attract and kill adult fruit flies, was tested in the laboratory and outdoors to determine effects of pre‐treatment diet and bait aging on mortality of Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Two spinosad‐based compounds, GF‐120 and Tracer® Ultra, had generated two distinctive dose–mortality responds, with LC80, LC90, and LC99 values of 2.4, 2.8, and 4.1 p.p.m., and 255, 479, and 1 143 p.p.m., respectively. The residues of GF‐120 drops, after feeding to the flies, generated 14.3% mortality. The droplet size of the baited spray plays an important role. The toxicity of large drops lasted more than that of small droplets. In the field, exposure to the sun further deteriorates the compound, which lost 50% of its toxicity within 6 days. Disappearance of the compound in the field, due to consumption by various insects, also played a role as 50% of the GF‐120 drops disappeared within 7 days. As mortality was directly related to the amount of insecticide eaten, the effect of GF‐120 depended on the feeding status of the flies: well‐fed flies were almost unaffected compared with starved ones. 相似文献