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Acidic pH Values (acidic + ph_value)
Selected AbstractsCross-talk involving extracellular sensors and extracellular alarmones gives early warning to unstressed Escherichia coli of impending lethal chemical stress and leads to induction of tolerance responsesJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2001R.J. Rowbury 1. Summary, 678 2. Introduction 2.1. Chemical and biological stress agents affecting enterobacteria, 678 2.2. Sensing of chemical and biological stress stimuli, 678 2.3. Intracellular sensors detect intracellularly-produced chemical stressing agents, 679 2.4. Intracellular sensors and intracellular induction components could delay response induction by extracellular chemical or biological stress agents, 680 2.5. Extracellular sensors and EICs give early warning of stress, 681 2.6. Disadvantages of extracellular components being needed for stress response induction, 682 2.7. Extracellular sensors and EICs allow stressed cells to warn unstressed ones, 682 2.8. A second role for some extracellular stress sensors, 683 3. Responses switched on by extracellular sensors and EICs 3.1. Involvement of EICs and ESCs in acid tolerance induction at pH 5·0 and at other mildly acidic pH values, 683 3.2. Further evidence for the obligate involvement of extracellular sensors and EICs in acid tolerance induction at pH 5·0, 684 3.3. On the nature of the acid pH tolerance-inducing ESC and EIC, 686 3.4. The acid tolerance ECs and their relation to other extracellular response-inducing components, 686 3.5. Extracellular components are needed for other inducible acid tolerance responses, 687 3.6. Involvement of EICs and extracellular sensors in acid tolerance in E. coli O157, 687 3.7. EICs involved in acid tolerance induction are diffusible, 687 4. Acid sensitization at alkaline pH and the role of extracellular sensor and EIC(s), 688 5. Responses affecting tolerance to alkali 5.1. Alkali sensitization at acidic pH, 688 5.2. Induced alkali tolerance at pH 9·0 and role of extracellular components, 688 6. Inducible tolerance to alkylhydroperoxides, 689 7. Are extracellular sensors and extracellular induction components needed for all stress responses?, 689 8. Altered responsiveness of extracellular sensors depending on growth conditions, 691 9. Protection of living cells from chemical stress by dead cultures, 691 10. How can intracellular levels of stress be detected?, 692 11. Are Nikolaev's extracellular ,protectants' and similar components related to EICs?, 693 12. Conclusions, 693 13. References, 694 [source] Predictive models of the combined effects of curvaticin 13, NaCl and pH on the behaviour of Listeria monocytogenes ATCC 15313 in brothJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2000A. Bouttefroy Thirty-three strains of Listeria monocytogenes belonging to different serotypes were tested for their sensitivity to curvaticin 13, an antilisterial bacteriocin produced by Lactobacillus curvatus SB13, using the well diffusion method in Institut Pasteur agar plates at 37 °C. No relationship between serotype and sensitivity was observed. The sensitivity of this species was strain-dependent and a large variation in tolerance to curvaticin 13 was observed. The combined effects of curvaticin 13 (0,160 AU ml,1), NaCl (0,6% w/v), pH values (5·0,8·2) and incubation time (0,24 h) were investigated on L. monocytogenes ATCC 15313 in trypcase soy,yeast extract broth at 22 °C. For this study, two Doehlert matrices were used in order to investigate the main effects of these factors and their different interactions. The results were analysed using the Response Surface Methodology. Curvaticin 13 had a major inhibitory effect and the response was NaCl concentration-, time- and pH-dependent. This inhibitory activity was the same at pH values between 6·6 and 8·2. Curvaticin 13 was bactericidic at acidic pH values, but the surviving cells resumed growth. For a short incubation time (12 h), the effectiveness of curvaticin 13 was maximal in the absence of NaCl. For longer incubation times (12,48 h), with high NaCl (6%) and curvaticin 13 concentrations (160 AU ml,1), the inhibition of L. monocytogenes was greater than that observed with NaCl or curvaticin 13 alone. [source] Formation of nitrosothiols from gaseous nitric oxide at pH 7.4JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 3 2002Carlo Alberto Palmerini Abstract Nitric oxide (NO) is generated in biological systems and plays important roles as a regulatory molecule. Its ability to bind to haem iron is well known. Moreover, it may lose an electron, forming the nitrosonium ion, involved in the synthesis of S -nitrosothiols (SNOs). It has been suggested that S -nitrosohaemoglobin (,SNO Hb) and low molecular weight SNOs may act as reservoirs of NO. SNOs are formed in vitro, at strongly acidic pH values; however, the mechanism of their formation at neutral pH values is still debated. In this paper we report the anaerobic formation of SNOs (both high- and low-molecular weight) from low concentrations of NO at pH 7.4, provided Hb is also present. We propose a reaction mechanism entailing the participation of Fehaem in the formation of NO+ and the transfer of NO+ either to Cys,93 of Hb or to glutathione; we show that this reaction also occurs in human RBCs. © 2002 Wiley Periodicals, Inc. J Biochem Mol Toxicol 16:135,139, 2002. DOI 10.1002/jbt.10028 [source] Identification and characterisation of the E951 artificial food sweetener by vibrational spectroscopy and theoretical modellingJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Niculina Peica Abstract Aspartame (E951), a very well-known dipeptide sweetener, approximately 150,200 times sweeter than sugar, is widely used in a variety of applications, especially in soft drinks. A drawback of E951 is its relatively low stability at high pH values and at high temperatures, thereby limiting its use. The changes observed in the very strong bands from the 1600,1300 cm,1 spectral region, characteristic to the ,(CO) mode coupled with the NH bending mode, allows to establish the species present in the Raman and SERS solutions at different concentrations and pH values. More exactly, a molecule protonation at the amino group was detected on going from basic to acidic pH values. The DFT calculated geometry, harmonic vibrational modes and Raman scattering activities of E951 were in good agreement with the experimental data and helped establish its SERS behaviour on silver surfaces. According to the DFT calculations performed, E951 can give rise to an intramolecular hydrogen bonding network, with lengths in the same range as the hydrogen bonds in the peptide unit moieties. Copyright © 2009 John Wiley & Sons, Ltd. [source] pH-Dependent Spectral Properties of HpIX, TPPS2a, mTHPP and mTHPC,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2001Beata, underlíková ABSTRACT Lower extracellular pH in tumors as compared to normal tissues has been proposed to be a factor contributing to the tumor selective uptake of several photosensitizers. Therefore, the pH dependence of absorption and fluorescence spectral properties of four different drugs relevant for photodynamic therapy (hematoporphyrin IX [HpIX], disulfonated meso -tetraphenylporphine [TPPS2a], meso -tetra(3-hydroxyphenyl)porphine [mTHPP] and meso -tetra(3-hydroxyphenyl)chlorin [mTHPC]) has been examined. Spectral analysis of the dyes dissolved in phosphate buffered saline (PBS) indicates pH-dependent modification in the physiologically important region (6.0,8.0) only in the case of HpIX. This modification is probably related to the protonation of carboxylic groups. Spectral changes of HpIX in PBS observed at acidic pH values <5, as well as those of the rest of the drugs (inflection points of titration curves occurred at about 5.1, 3.8 and 2.4 for TPPS2a, mTHPP and mTHPC, respectively), are likely to be due to the protonation of imino nitrogens. The tumor localizing properties of mTHPP and mTHPC reported in the literature appear to be due to factors other than pH-dependent changes in the lipophilicity of the drugs. [source] | |||||||||||||