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Amyloid fibril formation by proteins and their deposition in cells and tissues are associated with several amyloid-based disorders. Understanding the mechanism of amyloid fibril formation is thus of the utmost importance for the designing ligands that could prevent or inhibit the fibrillation process and help to treat of such disorders. We describe the stimulatory effect of sodium dodecyl benzenesulfonate (SDBS) on insulin amyloid fibrillation at pH 2.0 and the characterization of SDBS-induced insulin aggregation using spectroscopy and microscopy. We found that SDBS induced amyloid-like aggregates of insulin at sub-micellar (0.1-1.2 mM), but not post-micellar (≥2.0 mM) concentrations. The amyloid fibrillation of insulin induced by SDBS was kinetically rapid and escaped the lag phase. Far-UV CD findings suggested that the α-helical content of insulin transformed into cross-β structure and mixed α and β structures when incubated with sub-micellar and post-micellar SDBS concentrations, respectively. The overall results indicated that low, but not high SDBS concentrations induce amyloid-like insulin aggregates and fibrils., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Cancer as a multifactorial and smart disease is now considered a challenging problem. Despite many investigations on drug discovery, it remains incurable, in part, due to insufficient understanding of its special mechanisms. For the first time, we collaterally investigated the effect of acidosis on the contribution of apoptosis, necrosis, and autophagy in MDA-MB 231 cells. Our data showed that necrosis, apoptosis, and intracellular reactive oxygen species production drastically decreased from 48 to 72 hr while cell viability and autophagy increased along with a gap between the percentages. Eventually, the decrease of necrosis and apoptosis was related to upregulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and fatty acid synthetase, respectively. It seems that at the early stage of cancer progression, apoptosis is the main mechanism of cell mortality and afterward autophagy would be the main mechanism of cell survival. Therefore, at the acute phase of cancer, apoptotic inducer medications would be effective while at the chronic phase of cancer progression, autophagy inhibitor medication would be added as well. This eventually means that autophagy acts as both cell death and survival mechanisms at the onset of cancer progression with the approach towards cell survival. Besides other unknown cell survival mechanisms are involved in cell viability, except for apoptosis and necrosis inhibition and autophagy improvement. This study reiterates the inefficaciousness of autophagy inhibitor's medication at the onset of disease. It also emphasizes discovering other cell death mechanisms for cancer cell adaptation at the onset of disease with the aim of their targeting in cancer invasion therapy., (© 2018 Wiley Periodicals, Inc.)

Background: G-Quadruplex is a highly polymorphic structure, and its behavior in acidic condition has not been well studied., Methods: Circular dichroism (CD) spectra were used to study the conformational change of G-quadruplex. The thermal stabilities of the G-quadruplex were measured with CD melting. Interconversion kinetics profiles were investigated by using CD kinetics. The fluorescence of the inserted 2-Aminopurine (Ap) was monitored during pH change and acrylamide quenching, indicating the status of the loop. Proton NMR was adopted to help illustrate the change of the conformation., Results: G-Quadruplex of specific loop was found to be able to transform upon pH variation. The transformation was resulted from the loop rearrangement. After screening of a library of diverse G-quadruplex, a sequence exhibiting the best transformation property was found. A pH-driven nanoswitch with three gears was obtained based on this transition cycle., Conclusions: Certain G-quadruplex was found to go through conformational change at low pH. Loop was the decisive factor controlling the interconversion upon pH variation. G-Quadruplex with TT central loop could be converted in a much milder condition than the one with TTA loop. It can be used to design pH-driven nanodevices such as a nanoswitch., General Significance: These results provide more insights into G-quadruplex polymorphism, and also contribute to the design of DNA-based nanomachines and logic gates., (© 2013.)

Highlights • Acid-tolerant microalgae (AM) tolerated heavy metals (HMs) at pH 3.5. • Specific growth rate in AM increased in cultures grown on Mn and Zn. • Cellular analysis revealed the predominant intracellular accumulation of HMs. • Biodiesel production increased in HMs-grown AM at acidic pH. • First report on HMs removal and biodiesel production by AM at pH 3.5. Abstract Metals in traces are vital for microalgae but their occurrence at high concentrations in habitats is a serious ecological concern. We investigated the potential of two acid-tolerant microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, isolated from neutral environments, for simultaneous removal of heavy metals such as copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn), and production of biodiesel when grown at pH 3.5. Excepting Cu, the selected metals at concentrations of 10–20 mg L−1 supported good growth of both the strains. Cellular analysis for metal removal revealed the predominance of intracellular mechanism in both the strains resulting in 40–80 and 40–60% removal of Fe and Mn, respectively. In-situ transesterification of biomass indicated enhanced biodiesel yield with increasing concentrations of metals suggesting that both these acid-tolerant microalgae may be the suitable candidates for simultaneous remediation, and sustainable biomass and biodiesel production in environments like metal-rich acid mine drainages. [ABSTRACT FROM AUTHOR]

Incontinence-associated dermatitis (IAD) is a common problem in patients with faecal and/or urinary incontinence. Urine alters the normal skin flora and increases permeability of the stratum corneum and faecal enzymes on the skin contribute to skin damage. Faecal bacteria can then penetrate the skin, increasing the risk of secondary infection. However, IAD can be prevented and healed with timely and appropriate skin cleansing and skin protection. This includes appropriate use of containment devices. This article also looks at HARTMANN incontinence pads that have been developed to absorb the fluids that cause IAD and maintain the skin’s acidic pH. The acidic pH of the skin contributes to its barrier function and defence against infection. Therefore, maintaining an acidic pH will help protect the skin from damage. [ABSTRACT FROM AUTHOR]

The successful use of anaerobic reactors for bioremediation of acid mine drainage has been shown in systems with neutral pH. However, the choice of an efficient and suitable process for such wastewater must consider the capability of operating at acidic pH and in the presence of metals. This work studies the performance of an anaerobic batch reactor, under conditions of varying initial pH for its efficiencies in sulfate removal and metal precipitation from synthetic acid mine drainage. The chemical oxygen demand/sulfate (COD/SO42−) ratio used was 1.00, with ethanol chosen as the only energy and carbon source. The initial pH of the synthetic drainage was progressively set from 7.0 to 4.0 to make it as close as possible to that of real acid mine drainage. Metals were also added starting with iron, zinc, and finally copper. The effectiveness of sulfate and COD removal from the synthetic acid mine drainage increased as the initial pH was reduced. The sulfate removal increased from 38.5 ± 3.7% to 52.2 ± 3%, while the removal of organic matter started at 91.7 ± 2.4% and ended at 99 ± 1%. These results indicate that the sulfate reducing bacteria (SRB) community adapted to lower pH values. The metal removal observed was 88 ± 7% for iron, 98.0 ± 0.5% for zinc and 99 ± 1% for copper. At this stage, an increase in the sulfate removal was observed, which reaches up to 82.2 ± 5.8%. The kinetic parameters for sulfate removal were 0.22 ± 0.04 h−1with Fe, 0.26 ± 0.04 h−1with Fe and Zn and 0.44 ± 0.04 h−1with Fe, Zn, and Cu. [ABSTRACT FROM PUBLISHER]

Natural Mn oxides are largely biogenic in origin, formed via the microbial oxidation of Mn(II). These minerals are extremely efficient scavengers of heavy metals, yet to date microbial Mn oxide precipitation and subsequent heavy metal sorption have received little attention in mining-impacted environments, where heavy metal concentrations are elevated but (bio)geochemical conditions are typically unfavourable for both abiotic and biogenic Mn oxide precipitation, featuring acidic pH and low organic carbon contents. Here we investigate the formation of Mn oxide (bio)geochemical barrier layers, and the immobilisation of heavy metals in these layers, in soil profiles from a former uranium mining site in Ronneburg, Germany. Detailed soil profiling shows the site has an acidic soil pH that varies from 4.7 to 5.1 and Eh values from 640 to 660 mV. Using synchrotron X-ray diffraction and X-ray absorption spectroscopy, together with scanning electron microscopy and electron microprobe analysis, we find that the dominant Mn oxide present in the Mn oxide layers is a poorly crystalline hexagonal birnessite, akin to synthetic δ-MnO 2 , covering and cementing quartz grains. Using phylogenetic analysis based on 16S rDNA, we identify and characterise six strains of manganese oxidising bacteria (MOB) from the acidic Mn oxide layers which we subsequently culture to produce poorly crystalline hexagonal birnessite akin to that found at the study site. Specifically, we identify three Gram-positive spore-forming firmicutes affiliated to Bacillus safensis , Bacillus altitudinis and Brevibacillus reuszeri , which are able to oxidise Mn after initiating spore formation, two Gram-positive actinobacteria belonging to the genera Arthrobacter and Frondihabitans , and one Gram-negative proteobacteria belonging to the genus Sphingomonas . Geochemical thermodynamic speciation modelling indicates that the abiotic precipitation of Mn oxides in the Mn oxide layers is unfavourable and we suggest that the Mn oxides in the (bio)geochemical barriers at our study site are biogenically precipitated in an acidic soil environment. To our knowledge, this is the first report to identify the above six bacterial strains, and specifically identify spore-forming bacteria, as MOB in an acidic soil environment. We find that the poorly crystalline hexagonal birnessite precipitated in the Mn oxide layers efficiently immobilises Ba, Ni, Co, Cd, Zn and Ce, and as such we find that MOB and biogenically precipitated Mn oxides can exert a strong control on the fate and mobility of metals in mining-impacted environments. [ABSTRACT FROM AUTHOR]

Helicobacter pylori possesses intrabacterial nanotransportation systems ( ibNoTSs) for CagA and urease. Both systems are UreI-dependent and urea-independent, and activated by extrabacterial acid. The activation occurs/appears within 15 min after exposure to extrabacterial acid stimulation. Although it has been clarified that VacA is secreted via the type-V secretion machinery, it remains unclear how this toxin is transported toward the machinery. To clarify the intrabacterial nanotransportation system for H. pylori VacA, immunoelectron microscopic analysis was performed in this study. VacA shifted to the periphery of the bacterial cytoplasm at 30 min after the extracellular pH change, whereas CagA and urease did so within 15 min. Studies using an ureI-deletion mutant revealed that unlike CagA and urease transport, VacA transport was not UreI-dependent. VacA secretion was accelerated without an increase in the production of VacA 30 min after the exposure to extrabacterial acid. These findings indicated that H. pylori possesses a novel type of ibNoTS for VacA, which is different from that for CagA or urease, in response time and dependency of UreI. [ABSTRACT FROM AUTHOR]

This study evaluated the effects of an acute change in water pH (from pH 7.5 to 4.0, 5.0, 6.0, 7.5, 8.0 or 9.0) on several biochemical parameters in juveniles of the silver catfish, Rhamdia quelen . Ammonia levels decreased in the liver and increased in the muscle with increasing water pH. In the kidney, lower ammonia levels were observed at neutral pH. An increase in water pH decreased the glucose, glycogen and lactate levels in the liver and kidney (except for glycogen levels in the kidney and lactate levels in the liver, which presented lower levels at neutral pH). In muscle, the glucose and glycogen levels decreased with increasing water pH, whereas lactate levels tended to be lower at neutral pH. Gill and kidney Na + /K + -ATPase activities tended to increase in alkaline water, and the highest value was observed in fish exposed to pH 9.0. The optimal levels of the analyzed biochemical parameters occurred at neutral pH. In conclusion, exposure to acidic and alkaline pH changes the metabolic parameters of silver catfish as well as gill Na + /K + -ATPase activity. [ABSTRACT FROM AUTHOR]

The isolation of hematopoietic stem and progenitor cells (HSPCs) is critical for transplantation therapy and HSPC research, however current isolation techniques can be prohibitively expensive, time-consuming, and produce variable results. Selectin-coated microtubes have shown promise in rapidly isolating HSPCs from human bone marrow, but further purification of HSPCs remains a challenge. Herein, a biomimetic device for HSPC isolation is presented to mimic the acidic vascular microenvironment during trauma, which can enhance the binding frequency between L-selectin and its counter-receptor PSGL-1 and HSPCs. Under acidic pH conditions, L-selectin coated microtubes enhanced CD34+ HSPC adhesion, as evidenced by decreased cell rolling velocity and increased rolling flux. Dynamic light scattering was utilized as a novel sensor to confirm an L-selectin conformational change under acidic conditions, as previously predicted by molecular dynamics. These results suggest that mimicking the acidic conditions of trauma can induce a conformational extension of L-selectin, which can be utilized for flow-based, clinical isolation of HSPCs. [ABSTRACT FROM AUTHOR]

Abstract: Pin1 is closely associated with the pathogenesis of cancers and Alzheimer’s disease (AD). Previously, we have shown the characteristics of the thermal denaturation of Pin1. Herein, the acid-induced denaturation of Pin1 was determined by means of fluorescence emission, synchronous fluorescence, far-UV CD, ANS fluorescence and RLS spectroscopies. The fluorescence emission spectra and the synchronous fluorescence spectra suggested the partially reversible unfolding (approximately from pH 7.0 to 4.0) and refolding (approximately from pH 4.0 to 1.0) of the structures around the chromophores in Pin1, apparently with an intermediate state at about pH 4.0–4.5. The far-UV CD spectra indicated that acidic pH (below pH 4.0) induced the structural transition from α-helix and random coils to β-sheet in Pin1. The ANS fluorescence and the RLS spectra further suggested the exposure of the hydrophobic side-chains of Pin1 and the aggregation of it especially below pH 2.3, and the aggregation possibly resulted in the formation of extra intermolecular β-sheet. The present work primarily shows that acidic pH can induce kinds of irreversible structural changes in Pin1, such as the exposure of the hydrophobic side-chains, the transition from α-helix to β-sheet and the aggregation of Pin1, and also explains why Pin1 loses most of its activity below pH 5.0. The results emphasize the important role of decreased pH in the pathogenesis of some Pin1-related diseases, and support the therapeutic approach for them by targeting acidosis and modifying the intracellular pH gradients. [Copyright &y& Elsevier]

Abstract: The present study aims to investigate the electrochemical reduction of a range of H2O2 concentrations on a 1.5at.% SIMFUEL rotating disk electrode over the pH range 1–4. The peroxide reduction mechanism is determined to occur either on a UV-containing surface layer of composition UIV 1−2x UV 2x O2+x or on an adsorbed UV-containing surface intermediate depending on the surface composition which is determined by solution pH and H2O2 concentration. The UIV 1−2x UV 2x O2+x catalytic surface lattice layer, if formed, is stable and rotation disk studies have demonstrated that H2O2 reduction on this surface achieves the diffusion-controlled limit at sufficiently negative overpotentials. However, the adsorbed UV-containing surface intermediate is unstable and can be destroyed by electrochemical reduction to its original state, i.e. UO2, or by chemical oxidation to UVI prior to dissolution as UO2 2+. The instability of this surface intermediate limits its availability which prevents significant H2O2 reduction and yields currents below the diffusion-controlled limit. The occurrence of both reduction mechanisms demonstrates the influence of locally established surface compositions and the switch from one to the other appears to be controlled by surface diffusion conditions and the bulk pH and H2O2 concentrations. [Copyright &y& Elsevier]

Abstract: By using low temperature fluorescence spectroscopy, it has been shown that exposing chloroplast thylakoid membranes to acidic pH reversibly decreases the fluorescence of photosystem II while the fluorescence of photosystem I increases [P. Singh-Rawal et al. (2010) Evidence that pH can drive state transitions in isolated thylakoid membranes from spinach, Photochem Photobiol Sci, 9 830–837]. In order to shed light on the origin of these changes, we performed circular dichroism (CD) spectroscopy on freshly isolated pea thylakoid membranes. We show that the magnitude of the psi-type CD, which is associated with the presence of chirally ordered macroarrays of the chromophores in intact thylakoid membranes, decreases gradually and reversibly upon gradually lowering the pH of the medium from 7.5 to 4.5 (psi, polymer or salt induced). The same treatment, as shown on thylakoid membranes washed in hypotonic low salt medium possessing no psi-type bands, induces no discernible change in the excitonic CD. These data show that while no change in the pigment–pigment interactions and thus in the molecular organization of the bulk protein complexes can be held responsible for the observed changes in the fluorescence, acidification of the medium significantly alters the macro-organization of the complexes, hence providing an explanation for the pH-induced redistribution of the excitation energy between the two photosystems. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial. [Copyright &y& Elsevier]

The first stress that foodborne pathogens find upon ingestion is the very acidic pH of the stomach of the host. In addition, intracellular pathogens like Salmonella are submitted to low pH inside the host cells. Two general acid survival systems are found in these organisms: acid resistance mechanisms and acid tolerance responses. These mechanisms involve the synthesis of a series of acid shock proteins. Only a subset of these proteins is directly involved in acid survival. This is related to the fact that low pH is not only a stress to cope with, but it is also an important signal that indicates to the bacterium that it is in a potential host environment and that triggers the induction of many virulence genes. Asr is an acid shock protein that supports growth of Escherichia coli at moderate acidity. In this issue of Virulence, Allam et al. investigate the role of STM1485, the homologous of asr in Salmonella enterica serovar Typhimurium, in acid survival and virulence. Although STM1485 is not required for acid survival of S. enterica, it is necessary for intracellular replication in human epithelial cells and murine macrophages, and to prevent the progression of the Salmonella-containing vacuole along the degradative pathway. In addition, Allam et al. are able to show that the defects of the STM1485 mutant at the cellular level correlate with reduced virulence in the mouse model. [ABSTRACT FROM AUTHOR]

Abstract: BAX Inhibitor-1 (BI-1), a transmembrane protein on the endoplasmic reticulum, has been studied previously in various physio/pathological conditions, but not in bone cells. In this study, using the MG63 osteoblast cell line and osteoblasts differentiated from stem cells, the role of BI-1 was studied. First, expression of BI-1 was confirmed in osteoblasts, as well as osteoclasts, in mouse tibiae bone immunohistochemistry. For evaluation of a recently published property of BI-1, an acidic pH-dependent Ca2+ channel-like effect in osteoblasts, acidic pH-associated cell death, and pro-inflammatory cytokine release were examined. In MG63 osteoblasts, acidic pH induced a pH-dependent increase in cell death and ER stress, as determined by elevated expression of GRP78, CHOP, phospho-eIF2α, IRE-1α, spliced XBP-1, and phospho-JNK. In osteoblasts, mitochondrial Ca2+ also showed a strong pH-dependent increase. BI-1 knock-down using siRNA protected cells against acidic pH, regulating mitochondrial Ca2+ accumulation, possibly via the acidic pH-dependent Ca2+ channel-like effect of BI-1. BI-1 knock-down also resulted in inhibition of acidic pH-induced release of pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α. In addition, bone marrow stem cells were differentiated into human osteoblasts, which showed increased expression of BI-1 mRNA and protein. In differentiated primary human osteoblasts, acidic pH-associated cell death, mitochondrial Ca2+ accumulation, and pro-inflammatory cytokine release were more significant than in non-differentiated stem cells. In summary, endogenous expression of BI-1 is associated with acidic pH-induced Ca2+ release, cell death, and pro-inflammatory cytokine release in human osteoblasts. [Copyright &y& Elsevier]

Abstract: The extracellular pH is locally decreased in advanced atherosclerotic lesions, particularly in lipid-rich areas of the lesions. Since accumulation of LDL-derived cholesterol and formation of foam cells are key processes in atherogenesis, we tested here the effects of acidic pH on the uptake of native LDL. First, human monocytes were differentiated into macrophages in the presence of granulocyte–monocyte-colony stimulating factor (GM-CSF) after which native LDL was applied to the monocyte-derived macrophages at pH 5.5, 6.5, or 7.5 and the binding and uptake of LDL by macrophages were determined. The lower the pH was, the higher was the binding and uptake of LDL by macrophages. Also, acidic pH was found to increase the production of cell surface proteoglycans by macrophages and binding of LDL to the glycosaminoglycan chains of the proteoglycans. The acidity-induced increase in the uptake of LDL by macrophages could be inhibited by pretreating the cells with heparinase and chondroitinase as well as by inhibiting the production of proteoglycans with NaClO3. Thus, the observed increase in the uptake of native LDL to macrophages appears to depend on the increased ability of LDL to bind to cell surface proteoglycans at acidic pH. Taken together, our present results indicate that acidity increases the effective concentration of LDL on macrophage surfaces by increasing the amount of cell surface proteoglycans and by enhancing the binding of LDL to them and so promotes LDL uptake with ensuing foam cell formation. [Copyright &y& Elsevier]

Abstract: In tumor cell masses, the extracellular pH decreases below 6.5. The effect of external acidic pH on the efficacy of 24 chemical compounds including molecular-targeted inhibitors and anti-tumor reagents was investigated in human cancer cells. Lovastatin showed no cytotoxicity in mesothelioma or pancreatic carcinoma cells at concentrations up to 10μM and pH around 7.4, but 10μM lovastatin decreased the survival of these cells below 40% at acidic pH. Lovastatin inhibits HMG-CoA reductase, resulting in a decrease in the levels of cholesterol and prenylated proteins. An inhibitor of the former pathway showed pH-independent cytotoxic activity, whereas an inhibitor of the latter pathway had stronger activity at acidic pH. The inhibitory efficacy of cantharidin also increased at acidic pH. On the other hands, no pH dependency or slightly impaired efficacy at low pH conditions was observed in other 20 reagents, and especially, the activity of aphidicolin was suppressed under acidic conditions. These results suggested that screening under acidic conditions would be useful for developing new chemotherapeutic reagents. [Copyright &y& Elsevier]

Abstract: Mammalian gastric lipases are stable and active under acidic conditions and also in the duodenal lumen. There has been considerable interest in acid stable lipases owing to their potential application in the treatment of pancreatic exocrine insufficiency. In order to gain insights into the domain movements of these enzymes, molecular dynamics simulations of human gastric lipase was performed at an acidic pH and under neutral conditions. For comparative studies, simulation of dog gastric lipase was also performed at an acidic pH. Analyses show, that in addition to the lid region, there is another region of high mobility in these lipases. The potential role of this novel region is discussed. [ABSTRACT FROM AUTHOR]

Background and Aim: To evaluate the surface microhardness of mineral trioxide aggregate (MTA) mixed with various additives after exposure of their surface to acidic pH during hydration. Materials and Methods: White ProRoot MTA was mixed with various additives like saline, lidocaine, 2% calcium chloride and distilled water and packed into cylindrical polycarbonate tubes. Two groups, each of 32 specimens was prepared, with four subgroups and 8 samples under each subgroup. The two groups were exposed to 4.4 and 7.4 pH for 4 days. Vickers microhardness of the surface of each specimen was measured after exposure. The data obtained were subjected to one-way ANOVA and post hoc Tukey's test. Results: The greatest mean surface hardness value (74.4 ± 4.6) was observed following exposure to pH 7.4 of MTA with 2% CaCl2 and least value (17.2 ± 2.7) with saline. Tukey post-hoc test revealed that difference between the values of specimens for CaCl2, saline, lidocaine and distilled water were statistically signifi cant (p< 0.05). But among saline and distilled water at pH 4.4, it was not statistically signifi cant. Conclusion: Under the conditions of this study, surface hardness of MTA with 2%CaCl2 was not impaired in an acidic environment. [ABSTRACT FROM AUTHOR]

Abstract: Elevated temperature and decreased extracellular pH are hallmarks of inflammatory pain states. Dorsal root ganglia (DRG) neurons are integral in transferring painful stimuli from the periphery to central sites. This study investigated the effect of elevated temperatures on the response of DRG neurons to acute application of acidic solutions. At room temperature (22°C), in response to pH 5.5, there were a variety of kinetic responses consistent with differential expression of TRPV1 and ASIC channels. Increasing the temperature resulted in a significant increase in the peak and total current mediated by TRPV1 in response to an acidic solution. In contrast, the amplitude of a fast activating, rapidly inactivating ASIC1-like current was not affected by increasing the temperature but did result in an increased rate of desensitization that reduced the total current level. This effect on the rate of desensitization was temperature-dependent and could be reversed by returning to 22°C. Likewise, cells exhibiting slowly inactivating ASIC2-like responses also had temperature-dependent increase in the rate of desensitization. The ASIC2-like responses and the TRPV1 responses tended to decrease in amplitude with repetitive application of pH 5.5 even at 22°C. The rate of desensitization of ASIC-like currents activated by less acidic solutions (pH 6.8) was also increased in a temperature-dependent manner. Finally, acidic pH reduced threshold to trigger action potentials, however, the pattern of action potential firing was shaped by the distribution of ASIC and TRPV1 channels. These results indicate that the ambient temperature at which acidosis occurs has a profound effect on the contribution of ASIC and TRPV1 channels, therefore, altering the neuronal excitability. [Copyright &y& Elsevier]

Abstract: The PmrAB system is a two-component regulatory system that responds to extracellular iron and acidic pH. The role of the PmrAB system in Erwinia amylovora remains unknown so far. Our results showed that the pmrAB mutants were more resistant to strong acidic conditions than the wild type (WT) strain. The survival rate of the pmrAB mutants was much higher than that of WT when treated with polymyxin B. However, pmrAB mutants were more sensitive to extracellular iron than WT strain. These results demonstrated that the PmrAB system in E. amylovora renders the pathogen more susceptible to polymyxin B and acidic pH, but more resistance to excess iron. [Copyright &y& Elsevier]

Abstract: One of the essential steps in canine parvovirus (CPV) infection, the release from endosomal vesicles, is dominated by interactions between the virus capsid and the endosomal membranes. In this study, the effect of sphingomyelin and phosphatidyl serine on canine parvovirus capsid and on the phospholipase A2 (PLA2) activity of CPV VP1 unique N-terminus was analyzed. Accordingly, a significant (P ≤0.05) shift of tryptophan fluorescence emission peak was detected at pH 5.5 in the presence of sphingomyelin, whereas at pH 7.4 a similar but minor shift was observed. This effect may relate to the exposure of VP1 N-terminus in acidic pH as well as to interactions between sphingomyelin and CPV. When the phenomenon was further characterized using circular dichroism spectroscopy, differences in CPV capsid CD spectra with and without sphingomyelin and phosphatidyl serine were detected, corresponding to data obtained with tryptophan fluorescence. However, when the enzymatic activity of CPV PLA2 was tested in the presence of sphingomyelin, no significant effect in the function of the enzyme was detected. Thus, the structural changes observed with spectroscopic techniques appear not to manipulate the activity of CPV PLA2, and may therefore implicate alternative interactions between CPV capsid and sphingomyelin. [Copyright &y& Elsevier]

Abstract: The inhibitory activity of the serpins α1-proteinase inhibitor, α1-antichymotrypsin, α2-antiplasmin, antithrombin and C1-esterase inactivator is rapidly lost at pH 3 but slowly recovers at pH 7.4 with variable first-order rates (t 1/2 =1.4–19.2min). All except α1-antichymotrypsin undergo a variation in intrinsic fluorescence intensity upon acidification (midpoint ca. 4.5) with a slow bi-exponential return to the initial intensity at pH 7.4 (mean t 1/2 =2.3–23min). No correlation was found between the time of fluorescence recovery and that of reactivation. The acid-treated serpins are proteolyzed at neutral pH by their target proteinases. α1-Proteinase inhibitor was studied in more detail. Its acidification at pH 3 has a mild effect on its secondary structure, strongly disorders its tertiary structure, changes the microenvironment of Cys232 and causes a very fast change in ellipticity at 225nm (t 1/2 =1.6s). Neutralization of the acid-treated α1-proteinase inhibitor is an exothermic phenomenon. It leads to a much faster recovery of activity (t 1/2 =4±1min) than of fluorescence intensity (t 1/2 =23±19min), ellipticity (t 1/2 =32±4min) and change in total energy, indicating that the inhibitory activity of α1-proteinase inhibitor does not require a fully native structure. [Copyright &y& Elsevier]

The effect of acute exposure to different water pH levels on urinary excretion and plasma ion levels in silver catfish Rhamdia quelen was analysed. Fish were exposed to pH 4·0, 5·0, 7·5, 8·0, and 9·0 for 4 days and urine was collected. Other specimens were also exposed to the experimental pH for 24 h and blood was sampled. Urine flow rate, urine and plasma pH showed a significant trend to increase with the increase of water pH. Urinary Na+ excretion rate also increased and ammonia urinary excretion rate decreased with the increase of water pH. There was a significant trend to decrease volume, ammonia, Cl− and Na+ urinary excretion rate with increasing mass in fish exposed to all pH levels studied. Plasma ammonia levels showed a slight decrease in fish exposed to water pH from 4·0 to 8·0, but those exposed to water pH 9·0 presented the highest ammonia levels. Most plasma ions and urinary excretion changes observed in silver catfish exposed to acidic or alkaline water were similar to those already detected in rainbow trout Oncorhynchus mykiss. In addition, the kidney and urinary bladder might participate on acid–base balance in silver catfish, since urine pH changed according to plasma pH. [ABSTRACT FROM AUTHOR]

Abstract: Fe(III) can have a strong oxidizing effect in the presence of reductants at acidic pH, which may occur under anaerobic conditions or in regions of inflammation. Low density lipoprotein (LDL) oxidation with Fe(III) and homocysteine/cystine at acidic pH provoked mainly formation of lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS) in the absence of significant protein modification. Even when oxidized to a high TBARS content, LDL oxidized at acidic pH was not cytotoxic when added to THP-1 monocytes in a concentration causing cell death when LDL was oxidized to a similar TBARS content at plasma pH with Fe(III) or Cu(II) in the presence or absence of homocysteine/cystine. Inducible nitric oxide production by RAW264.7 mouse macrophages was only weakly inhibited by LDL oxidized at acidic pH, even if acetylated before oxidation to increase uptake, as compared to LDL oxidized with Cu(II) at plasma pH to a similar TBARS content or anodic electrophoretic mobility. LDL oxidized at acidic pH may mainly induce protective mechanisms against oxidative stress while causing little acute damage of cells. [Copyright &y& Elsevier]

Abstract: Metal-catalyzed LDL oxidation is enhanced by the presence of homocysteine. In this study, the effectiveness of ascorbic acid against low-density lipoprotein (LDL) oxidation by iron(III) and copper(II) in the presence of homocysteine and the main plasma disulfide cystine was investigated. Relative to the degree of LDL oxidation reached in the absence of antioxidants, ascorbic acid was particularly effective against iron-catalyzed LDL oxidation at pH 6.0. This can be explained from its stability under acidic conditions and is likely to be important in ischemia, in inflammation and exhausting exercise. At pH 7.4, an ascorbic acid concentration at least as high as the concentration of homocysteine might be necessary to efficiently inhibit LDL oxidation by iron(III) and copper(II) in the presence of homocysteine and cystine. Histidine increased the efficiency of ascorbic acid as an antioxidant against copper-mediated oxidation in this system. The capacity of homocysteine to regenerate ascorbic acid from dehydroascorbic acid appeared to play a minor role in inhibition of ascorbic acid oxidation by copper as compared to copper chelation by homocysteine. [Copyright &y& Elsevier]

Colored, low molecular weight pI markers have been developed for isoelectric focusing (IEF) in acidic pH range. Their isoelectric points (pIs) were determined by direct measurement of the pH of the focused bands after completion of IEF on polyacrylamide gels. The practicable suitability of the proposed pI markers as pI standards for IEF was tested by applying gel IEF. The acidic pH gradient was created either by commercial synthetic carrier ampholytes or by mixture of simple buffers consisting of acids (non-ampholytes) and ampholytic buffers. By applying simple acids, it was possible to extend the acidic pH range beyond those achievable with commercial synthetic carrier ampholytes. By using an experimental arrangement without electrode electrolyte reservoirs with electrodes creating the fixed end of the gel, the strongly acidic pH gradient was stable even for prolonged focusing time. [ABSTRACT FROM AUTHOR]

The objective of the present study was to examine the combined effects of zinc compounds with different acidic pH levels on the aerobic growth of a S. typhimurium poultry isolate in either rich or minimal media. When overall main effects of pH levels of medium or concentrations of Zn compounds were compared, growth rates of the S. typhimurium poultry isolate were significantly ( p < 0.05) decreased by stepwise increase of pH levels of medium (pH 4, 5, 6, and 7) or concentrations (0.67, 3.35, and 6.03%) of Zn compounds (Zn acetate and Zn sulfate). In general growth rates of S. typhimurium poultry isolate appeared to be more reduced by Zn acetate than by Zn sulfate and more reduced in minimal media compared to rich media. [ABSTRACT FROM AUTHOR]

Abstract: The Baylis–Hillman reaction has been successfully performed under aqueous acidic conditions at pH1, using a range of substrates and tertiary amines as catalysts. [Copyright &y& Elsevier]