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D. Slameňová 《Folia microbiologica》1972,17(4):274-280
The fraction of inducedtrp
+ reversions in the strains ofEscherichia coli B/rthy
−
trp
−
Hcr
+ andEscherichia coli B/rthy
−
trp
−
Hcr
− was studied in the course of starvation for an essential amino acid. UV light as a mutagenic factor was used. It was found
that there is a decrease in the proportion of inducedtrp
+ reversions in the strain ofHcr
+ type during starvation. Such a decrease was however observed only with that fraction oftrp
+ reversions which is expressed in selective plates where several divisions of irradiated cells are caused. The proportion
oftrp
+ reversions expressed on minimal plates does not change during starvation. With the strain ofHcr
− type the proportion of inducedtrp
+ mutations remains unaltered irrespective of the nature of the selective plates. 相似文献
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Selection of antigen loss variants from the BW5147 cell line after chemical mutagenesis, using antibodies to Thy-1.1, Ly-6.2 and H9/25 allospecificities, produced cell lines with a pleiotropic defect in cell surface antigen expression; selection against any antigen led to the loss of all three determinants. The genetic basis for the mutant phenotype has been analyzed by gene complementation by somatic cell hybridization between Ly-6
– or H9/25
– and Thy-1
– mutants, which comprise different Thy-1 gene complementation classes. The Ly-6
– and H9/25
– mutants can be classified as belonging to either the A or E Thy-1– mutant class. 相似文献
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Summary The current-voltage relationship of carrier-mediated, passive and active ion transport systems with one charge-carrying pathway can exactly be described by a simple reaction kinetic model. This model consists of two carrier states (one inside, one outside) and two pairs (forwards and backwards) of rate constants: a voltage-dependent one, describing the transport of charge and a voltage-insensitive one, summarizing all the other (voltage-independent) reactions. For the electrogenic Cl– pump inAcetabularia these four rate constants have been determined from electrical measurements of the current-voltage relationship of the pump (Gradmann, Hansen & Slayman, 1981;in: Electrogenic Ion Pumps, Academic Press, New York). The unidirectional Cl– efflux through the pump can also be calculated by the availiable reaction kinetic parameters.36Cl– efflux experiments on singleAcetabularia cells with simultaneous electrical stimulation (action potentials) and recording, demonstrate the unidirectional Cl– efflux to depend on the membrane potential. After subtraction of an efflux portion which bypasses the pump, agreement is found between the measured flux-voltage relationship and the theoretical one as obtained from the reaction kinetic model and its parameters from the electrical data. 相似文献
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M. E. H. Osman 《Russian Journal of Plant Physiology》2014,61(1):33-37
Thylakoids were isolated from the leaves of three different plants (Pisum sativium L., Lactuca sativa L., and Raphanus sativus L.). The addition of HCO 3 ? to a suspension of salt-and HCO 3 ? -epleted thylakoids (suspended in salt-free medium) raised the rate of O2 evolution up to fourfold. This stimulation could be partially replaced by the addition of chloride or nitrate ions. However, the addition of HCO 3 ? in the presence of Cl? or NO 3 ? resulted in a higher stimulation of O2 evolution (sixfold in the presence of nitrate and sevenfold in the presence of chloride). On the other hand, the addition of HCO 3 ? to the thylakoids depleted from salt only raised the rate of O2 evolution by 10–15%, whereas 40–70% was obtained by the addition of nitrate or chloride ions. The fluorescence induction studies indicated a significant decrease in the yield of the variable fluorescence of the salt- and HCO 3 ? -depleted thylakoids. A partial increase in the fluorescence yield was obtained by the addition of HCO 3 ? alone. A typical fluorescence induction curves were obtained by the addition of HCO 3 ? in the presence of Cl? or NO 3 ? ions. The data obtained suggest a similar role for chloride and nitrate ions in O2 evolution in the Hill-reaction, which is restricted at the donor side of photosystem II, whereas bicarbonate plays its role at both sides (acceptor and donor sides). The presented data are those obtained for the thylakoids of P. sativium, which were more or less similar to those obtained for L. sativa and R. sativus. 相似文献
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Xinqiang Guo Kai Chen Yang Wen Rong Li Shunpeng Li Jiandong Jiang 《International biodeterioration & biodegradation》2009,63(5):576-581
Bioremediation of pollutants in natural environments is affected by many factors, such as bacterial survival, motility, and chemotaxis. However, these roles in in-situ biodegradation of organophosphorus pesticides have not been examined extensively. In this paper, a highly effective methyl-parathion (MP) degrading strain, Pseudomonas putida DLL-1, which also demonstrates motile ability and chemotactic response toward MP, was selected as the research material. A leuB? auxotroph mutant A3-27 and fliC? non-motility mutant a4-8 were first constructed by random insertion of the kanamycin gene into the chromosome of P. putida DLL-1 with the mini-transposon system. Biodegradation of MP in liquid medium and soil microcosms by A3-27, a4-8 and a previously constructed cheA? non-chemotaxis mutant P. putida DAK were compared. The kinetic parameters for MP degradation were all similar in the well-mixed liquid systems. However, in soil microcosms, all the three mutants had lower degrading rates compared with wild-type P. putida DLL-1. The auxotroph mutant A3-27 had the lowest degrading rate and could only degrade 25.7–34.2% MP in 5 days, and the non-motility mutant a4-8 and non-chemotaxis mutant DAK could only degrade 53.5–68.1% and 64.3–85.7% MP, respectively. This paper emphasizes, for the first time, the use of non-auxotroph bacteria for efficient removal of organophosphorus pesticides in contaminated sites, and also points out the importance of select microorganisms with specific motile or chemotactic affinities in optimizing pesticide bioremediation. 相似文献
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Talita Rafaele D’Agostini Mantovani Henrique Susumu Tanaka Suzana Harue Umeo Lienine Luiz Zaghi Junior Juliana Silveira do Valle Luzia Doretto Paccola-Meirelles Giani Andrea Linde Nelson Barros Colauto 《Indian journal of microbiology》2012,52(3):484-488
Alternative substrates for cryopreservation at −20 °C have been little explored for basidiomycetes and could bring new possibilities of lower cost cryopreservation. Nevertheless, freezing temperatures between −15 and −60 °C are very challenging because they frequently result in cryoinjuries. The objective of this study was to evaluate substrates associated to cryoprotective agents for Pleurotus ostreatus cryopreservation at −20 or −70 °C in order to develop alternative techniques for basidiomycete cryopreservation. P. ostreatus was grown on potato dextrose agar or whole grains of oat, wheat, rice or millet and transferred to cryovials with cryoprotective solution with 1 % dimethyl sulfoxide, 5 % glycerol, 10 % saccharose, 4 % glucose, 6 % polyethylene glycol-6000 or 5 % malt extract. The mycelium in the cryovials were cryopreserved at −20 or −70 °C and recovered for evaluation of the mycelial growth viability after 1 and 3 years. Both substrates and cryoprotectants affect the viability of the mycelial growth cryopreserved at −20 or −70 °C; wheat grains combined with cryoprotectants such as saccharose or glucose are effective for keeping mycelium viable after cryopreservation at −20 °C for 1 or 3 years; for cryopreservation at −70 °C after 1 or 3 years, any substrate combined with any cryoprotectant is effective for preserving the mycelium viable, except for millet grains with polyethylene glycol after 3 years; semi-permeable cryoprotective agents such as saccharose and glucose are the most effective for cryopreservation at −20 or −70 °C for at least 3 years. 相似文献
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The effect of glucose starvation during the pre-irradiation period on the UV resistance and on the DNA melting points was investigated. The radio-resistance ofEscherichia coli 15 T?U? his ? increases markedly with the length of starvation. The DNA melting point of an exponentially growing culture is decreased by a dose of 500 erg/mm2 by 3 C. The same dose does not affect the melting point of DNA in a prestarved culture. 相似文献
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Influx, efflux and net uptake of NO
3
–
was studied in Pisum sativum L. cv. Marma in short-term experiments where 13NO
3
–
was used to trace influx. The influx rate in N-limited plants was similar both during net uptake at external concentrations of around 50 M, and at low external NO
3
–
concentrations (4–6 M) when net uptake was practically zero. Efflux could be inferred from discrepancies between influx and net uptake but was never very high in the N-limited plants during net uptake. Close to the threshold concentration for not NO
3
–
uptake, efflux was high and equalled influx. Thus, the threshold concentration can be regarded as a NO
3
–
compensation point. The inclusion of NH
4
+
in the outer medium decreased influx by about 40% but did not significantly affect efflux. The roles of NO
3
–
fluxes and nitrate-reductase activity in regulating/limiting NO
3
–
utilization are discussed.Abbreviations DW
dry weight
- FW
fresh weight
- RN
relative nitrogen addition rate 相似文献
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Summary Active HCO
3
t-
secretion in the anterior rectal salt gland of the mosquito larva,Aedes dorsalis, is mediated by a 11 Cl–/HCO
3
–
exchanger. The cellular mechanisms of HCO
3
–
and Cl– transport are examined using ion- and voltage-sensitive microelectrodes in conjunction with a microperfused preparation which allowed rapid saline changes. Addition of DIDS or acetazolamide to, or removal of CO2 and HCO
3
–
from, the serosal bath caused large (20 to 50 mV) hyperpolarizations of apical membrane potential (V
a) and had little effect on basolateral potential (V
bl). Changes in luminal Cl– concentration alteredV
a in a repid, linear manner with a slope of 42.2 mV/decaloga
Cl
l
–. Intracellular Cl– activity was 23.5mm and was approximately 10mm lower than that predicted for a passive distribution across the apical membrane. Changes in serosal Cl– concentration had no effect onV
bl, indicating an electrically silent basolateral Cl– exit step. Intracellular pH in anterior rectal cells was 7.67 and the calculated
was 14.4mm. These results show that under control conditions HCO3 enters the anterior rectal cell by an active mechanism against an electrochemical gradient of 77.1 mV and exits the cell at the apical membrane down a favorable electrochemical gradient of 27.6 mV. A tentative cellular model is proposed in which Cl enters the apical membrane of the anterior rectal cells by passive, electrodiffusive movement through a Cl–-selective channel, and HCO
3
–
exits the cell by an active or passive electrogenic transport mechanism. The electrically silent nature of basolateral Cl– exit and HCO3 entry, and the effects of serosal addition of the Cl–/HCO3 exchange inhibitor, DIDS, on
and transepithelial potential (V
ic) suggest strongly that the basolateral membrane is the site of a direct coupling between Cl– and HCO
3
–
movements. 相似文献
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M. Missori M. Papi G. Maulucci G. Arcovito G. Boumis A. Bellelli G. Amiconi M. De Spirito 《European biophysics journal : EBJ》2010,39(6):1001-1006
Ischemic heart disease is the leading cause of serious morbidity and mortality in Western society. One of the therapeutic
approaches is based on the use of thrombolitic drugs that promote clot lysis. Even if the mechanisms leading to clot lysis
are not completely understood, it is widely accepted that they depend on the complex biochemical reactions that occur among
fibrin fibers and fibrinolitic agents, and by their ready diffusion into the fibers. Here we investigate the effects of specific
anions on the architecture of protofibrils within fibrin fibers in fibrin gels prepared in a para-physiological solution.
The results obtained through small-angle X-ray scattering (SAXS) demonstrate that the characteristic axial and longitudinal
repeat distances among protofibrils are strongly affected by the action of Cl− and F− anions. 相似文献
19.
Secretion of bicarbonate has been described for distal nephron epithelium and attributed to apical Cl–/HCO
3
–
exchange in beta-intercalated cells. We investigated the presence of this mechanism in cortical distal tubules by perfusing these segments with acid (pH 6) 10 mm phosphate Ringer. The kinetics of luminal alkalinization was studied in stationary microperfusion experiments by double-barreled pH (ion-exchange resin)/1 m KCl reference microelectrodes. Luminal alkalinization may be due to influx (into the lumen) of HCO
3
–
or OH–, or efflux of H+. The magnitude of the Cl–/ HCO
3
–
exchange component was measured by perfusing the lumen with solutions with or without chloride, which was substituted by gluconate. This component was not different from zero in control and alkalotic (chronic plus acute) Wistar rats. Homozygous Brattleboro rats (BRB), genetically devoid of antidiuretic hormone, were used since this hormone has been shown to stimulate H+ secretion, which could mask bicarbonate secretion. In these rats, no evidence for Cl–/HCO
3
–
exchange was found in control BRB and in early distal segments of alkalotic animals, but in late distal tubule a significant component of 0.14±0.033 nmol/cm2 · sec was observed, which, however, is small when compared to the reabsorptive flow found in control Wistar rats, of 0.95±0.10 nmol/cm2 · sec. In addition, 5×10–4
m SITS had no effect on distal bicarbonate reabsorption in controls as well as on secretion in alkalotic Wistar and Brattleboro rats, which is compatible with the absence of effect of this drug on the apical Cl–/HCO
3
–
exchange in other tissues. It is concluded that most distal alkalinization is not Cl– dependent, and that Cl–/HCO
3
–
exchange may be found in cortical distal tubule, but its magnitude is, even in alkalosis, markedly smaller than the reabsorptive flux, which predominates in the rats studied in this paper, keeping luminal pH lower than that of blood. 相似文献
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M. J. Beilby 《The Journal of membrane biology》1981,62(3):207-218
Summary The changes in the cytoplasmic Cl– concentration, [Cl–]
c
, are monitored at the time of withdrawal (starvation) and subsequent replacement of Cl– in the outside medium. The measurement technique exploits the involvement of Cl– inChara excitation. The transient clamp current due to Cl–,I
Cl, is separated from other excitation transients through Hodgkin-Huxley (HH) equations, which have been adjusted toChara. TheI
Cl amplitude depends on HH parameters, [Cl–]
c
and the maximum membrane conductance to Cl–,
. The results are discussed in terms of these quantities.I
Cl and
were found to fall after 6–10 hr of Cl– starvation, thus supporting the hypothesis that [Cl–
c
decreases in Cl–-free medium. The best HH fit to starved data was obtained with [Cl–
c
=3.5mm. The time-course forI
Cl decline is considerably slower than the time-course of the rise of the starvation-stimulated influx. As cells starved for periods longer than 24 hr are re-exposed to Cl–, it is revealed that while [Cl–]
c
remains low during long starvation,
increases to values greater than those of the normal cells. Such differences among cells starved for various lengths of time have not been detected previously. 相似文献