Proton/electron stoichiometry of mitochondrialbc 1 complex. Influence of pH and transmembrane δpH

The effect of pH and transmembrane pH on the efficiency of the proton pump of the mitochondrialbc ₁ complex bothin situ and in the reconstituted state was studied. In both cases the H⁺/e ^– ratio for vectorial proton translocation by thebc ₁ complex respiring at the steady state, under conditions in which the transmembrane pH difference (pH) represents the only component of the proton motive force (p), was significantly lower than that measured under level flow conditions. The latter amounts, at neutral pH, to 1 (2 including the scalar H⁺ release). In the reconstituted system steady-state pH was modulated by changing the intravesicular buffer as well as the intra/extra-liposomal pH. Under these conditions the H⁺/e^– ratio varied inversely with the pH. The data presented show that pH exerts a critical control on the proton pump of thebc ₁ complex. Increasing the external pH above neutrality caused a decrease of the level flowH ⁺/e ^– ratio. This effect is explained in terms of proton/electron linkage inb cytochromes.     

Intracellular pH of baker’s yeast

The distribution of bromophenol blue between the cell and the medium was used to calculate the intracellular pH of yeast. In buffered media the intracellular pH exhibited a plateau at pH _i =5.8 for low external pH values and another at pH _i =7.6 for high external pH values. The production of H ions by the yeast during utilization of glucose is not accompanied by an alkalinization of the cell interior. The pH _i even decreases somewhat in the presence of glucose and K ions.

1. (1)
   Внутриклеточный pH дрожжей вычисляли на основании распределения бромфеноловой сини между клетками и средой.     
   
   

pH responsiveness of fibrous assemblies of repeat-sequence amphipathic α-helix polypeptides

We reported previously that our designed polypeptide α3 (21 residues), which has three repeats of a seven-amino-acid sequence (LETLAKA)₃, forms not only an amphipathic α-helix structure but also long fibrous assemblies in aqueous solution. To address the relationship between the electrical states of the polypeptide and its α-helix and fibrous assembly formation, we characterized mutated polypeptides in which charged amino acid residues of α3 were replaced with Ser. We prepared the following polypeptides: 2Sα3 (LSTLAKA)₃, in which all Glu residues were replaced with Ser residues; 6Sα3 (LETLASA)₃, in which all Lys residues were replaced with Ser; and 2S6Sα3 (LSTLASA)₃; in which all Glu and Lys residues were replaced with Ser. In 0.1M KCl, 2Sα3 formed an α-helix under basic conditions and 6Sα3 formed an α-helix under acid conditions. In 1M KCl, they both formed α-helices under a wide pH range. In addition, 2Sα3 and 6Sα3 formed fibrous assemblies under the same buffer conditions in which they formed α-helices. α-Helix and fibrous assembly formation by these polypeptides was reversible in a pH-dependent manner. In contrast, 2S6Sα3 formed an α-helix under basic conditions in 1M KCl. Taken together, these findings reveal that the charge states of the charged amino acid residues and the charge state of the Leu residue located at the terminus play an important role in α-helix formation.     

Effect of pH and Glucose on the Stability of α-lactalbumin

The objective of this study is to understand the influence of pH and effect of cosolvent (glucose) on the stabilization of bovine α-lactalbumin by using ultrasonic techniques. Values of density, ultrasonic velocity and viscosity were measured for bovine α-lactalbumin (5 mg/ml) dissolved in phosphate buffer (pH 2, 5, 7, 9 and 12) solutions mixed with and without the cosolvent at 30 °C. These measurements were used to calculate few thermo-acoustical parameters such as adiabatic compressibility, intermolecular free length, acoustic impedance, relaxation time, relative association constant, the partial apparent specific volume and the partial apparent specific adiabatic compressibility for the said systems. The obtained results revealed a strong comparison between the effects of acidic and alkaline pH values on protein denaturation, i.e., the acidic pH are instantaneous and are of less magnitude whereas alkaline pH are slower but sharper. Further the present study supports the fact that the presence of glucose stabilizes α-lactalbumin against denaturation due to pH variation, which may be due to the strengthening of non-covalent interactions and the steric exclusion effect.     

Contribution of ΔpH and ΔE to Photosynthesis of Chlamydomonas Reinhardtii

The contribution of two components (pH and E) of the proton motive force to photosynthesis of C. reinhardtii was studied. Valinomycin, a photophosphorylation uncoupler, decreased significantly the fast phase (related mainly to the membrane electric potential) of millisecond delayed light emission (ms-DLE) of C. reinhardtii. Nigericin, another photophosphorylation uncoupler, decreased the slow phase (related mainly to the proton gradient) and partly also the fast phase of ms-DLE. Both valinomycin and nigericin decreased the net ATP content and photosynthetic rate of C. reinhardtii, but the inhibition by nigericin was stronger than that by valinomycin. Hence both components of the proton motive force contribute to photosynthesis and although the contribution of pH is larger than that of E, the latter is not negligible in photosynthesis of C. reinhardtii.     

Control of Cl− influx inChara by internal pH

Summary The possible regulation of Cl^– influx inChara by the cytoplasmic Cl^– concentration and cytoplasmic pH was investigated using both intact and intracellularly perfused cells. In perfused cells Cl^– influx was sensitive to changes in the internal Cl^– concentration but only when the concentration was less than 1mm.In intact cells the metabolic inhibitors, CCCP, DCMU, and oligomycin which inhibit Cl^– influx also reduced the cytoplasmic pH. A correlation between ATP concentration and cytoplasmic pH was shown to apply when the ATP concentration was lowered using these inhibitors. The possible relationships between ATP status, cytoplasmic pH, and Cl^– influx are discussed.     

Rat small-intestinal β-galactosidases: Influence of pH on the hydrolysis of different substrates

1. The influence of pH and the kind of buffer on the hydrolysis of lactose and four hetero-β-galactosides (phenyl β-galactoside, o-nitrophenyl β-galactoside, p-nitrophenyl β-galactoside and 6-bromo-2-naphthyl β-galactoside) by homogenates of rat small-intestinal mucosa has been studied. 2. There are at least two β-galactosidases present in the homogenates, one with optimum pH3–4 and another with optimum pH5–6. 3. The enzyme with the lower pH optimum is mainly a heterogalactosidase. It hydrolyses lactose slowly. The other enzyme is mainly a disaccharidase, since it hydrolyses lactose much more rapidly than the heterogalactosides. 4. Under the conditions used, citrate had an inhibitory effect on the 6-bromo-2-naphthyl β-galactosidase activity at pH3–4, but did not influence the 6-bromo-2-naphthyl β-galactosidase activity at pH5–6 or the hydrolysis of the other substrates at any pH.     

The binding of inhibitors to α-chymotrypsin at alkaline pH

1. The binding of the competitive inhibitor N-acetyl-d-tryptophan amide to alpha-chymotrypsin has now been studied at pH values up to 10.6, by the technique of equilibrium dialysis. 2. This binding depends on the ionization of a group on the free enzyme with apparent pK(a) 9.3 at 5 degrees . 3. This group is tentatively identified as that responsible for an enzyme conformation change at high pH values, on which the catalytic activity of the enzyme also depends.     

Review of rotifers and crustaceans in highly acidic environments of pH values ≤3

A review of the literature on rotifers and crustacean zooplankton in highly acidic environments revealed that data from eleven aquatic environments on three continents (America, Europe, Japan) with a pH 3 are available. Seven sites are influenced by volcanism or weathering processes in the catchment area, four others originated from human mining activities. Species richness was generally low. Only 16 species are found and 1–11 species are reported for each area. These studies clearly show that small littoral or benthic rotifers predominate over crustaceans under highly acidic conditions. In the Lusatian mining area (Germany), all lakes are colonized by zooplankton, even the most acidic one with a pH of 2.3. The core community consists of the rotifers Cephalodella hoodi, C. gibba, Elosa worallii and Rotaria rotatoria, with C. hoodi and E. worallii the most abundant. Larger species, such as the rotifer Brachionus sericus or the cladoceran Chydorus sphaericus, occur at a pH close to 3. A similar pattern is reported from acidic mining lakes in Illinois, U.S.A. Many of these species can also be found in less acidic softwater or even alkaline environments due to the tolerance of a broad range of pH values. Elosa worallii and Brachionus sericus are probably the most acidophilic rotifer species, though at least the latter can also grow at neutral pH in the laboratory. Clear understanding of the pH limits of B. sericus in nature may also have been complicated by the fact that it has probably in the past been wrongly named as B. urceolaris (phenotype `sericus'). The typical B. urceolaris cannot tolerate extremely low pH. Overall, generalist species with a worldwide distribution seem to play the major role in the colonization of anthropogenic highly acidic lakes.     

Pressure-induced inactivation of E. coli β-galactosidase: influence of pH and temperatur

In order to assess the feasibility of a high-pressure immunodesorption process using a β-galactosidase-anti-/3-galactosidase complex as a model, the influence of high hydrostatic pressure on the inactivation of E. coli /3-galactosidase has been investigated. The irreversible activity loss of β-galactosidase was studied as a function of pH and temperature for pressures comprised between atmospheric pressure and 500 megapascal (MPa; 1 MPa = 10 bar). This enabled us to establish a practical pressure-temperature diagram of stability for this enzyme. The stability domains determined thus appeared to be strongly dependent on the pH under atmospheric pressure of the phosphate buffer employed for pressurisation. Therefore, to interpret meaningfully this result, the influence of pressure on the pH-activity curve of β-galactosidase was investigated by using a high-pressure stopped-flow device. It appeared that the pH-activity curve of this enzyme was also reversibly affected by pressures lower than 150 MPa. An interpretation of these results in relation to the high-pressure induced changes of ionisation constants is proposed. For our practical purpose, the implications for the elaboration of a high-pressure immunodesorption process using /3-galactosidase as a tag, are discussed.     

“In vivo” pH values of the estrous reproductive tract of the gilt

The hydrogen ion concentration of the fluids of various portions of the reproductive tract was determined in 6 estrous gilts. Determinations were made with a pH cardiovascular catheter electrode placed in the lumen of the oviduct, uterus, cervix and vagina and a reference electrode placed in the peritoneal cavity. The mean pH values were 7.02, 6.98, 7.49, and 6.61 for the oviduct, uterus, cervix and vagina, respectively.     

Screening of β-fructofuranosidase-producing microorganisms and effect of pH and temperature on enzymatic rate

Seventeen different strains of filamentous fungi were grown in batch cultures to compare their abilities for the production of β-fructofuranosidase. Three of them, Aspergillus oryzae IPT-301, Aspergillus niger ATCC 20611 and strain IPT-615, showed high production with total fructosyltransferase activity higher than 12,500 units l⁻¹. In addition, the β-fructofuranosidases of those strains have a high fructosyltransferase activity-to-hydrolytic activity ratio. The temperature and pH effects on the sucrose-β-fructofuranosidase reaction rate were studied using a 2² factorial experimental design. The comparative analysis of the tested variable coefficients shows that the variable pH contributes mostly to the changes in the fructosyltransferase and hydrolytic rates and in the V _t/V _h ratio. At 40 and 50°C, there were no significant differences between the fructosyltransferase and hydrolytic velocities of these enzymes.     

Effects of pH and temperature on the survival of coliphages MS2 and Qβ

The RNA F-specific coliphages, MS2 and Q, have been used as virus indicators in water and wastewater studies. It is therefore useful to have a good understanding concerning the effects of environmental factors on their survival in order to choose an appropriate candidate for assessing microbial safety in relation to water quality management. The effects of pH and temperature on the survival of these two coliphages were investigated. MS2 survived better in acidic conditions than in an alkaline environment. In contrast, Q had a better survival rate in alkaline conditions than in an acidic environment. The inactivation rates of both coliphages were lowest within the pH range 6–8 and the temperature range 5–35°C. The inactivation rates of both coliphages increased when the pH was decreased to below 6 or increased to above 8. The inactivation rates of both coliphages increased with increasing temperature. Q behaved peculiarly in extreme pH buffers, i.e. it was inactivated very rapidly initially when subjected to an extreme pH environment, although the inactivation rate subsequently decreased. In general, MS2 was a better indicator than Q. However, within the pH range 6–9 and at temperatures not above 25°C, either MS2 or Q could be used as a viral indicator.     

Importance of co-cultivation medium pH for successful Agrobacterium-mediated transformation of Lilium × formolongi

An efficient system for Agrobacterium-mediated transformation of Lilium × formolongi was established by preventing the drastic drop of pH in the co-cultivation medium with MES. Meristematic nodular calli were inoculated with an overnight culture of A. tumefaciens strain EHA101 containing the plasmid pIG121-Hm which harbored intron-containing β-glucuronidase (GUS), hygromycin phosphotransferase (HPT), and neomycin phosphotransfease II (NPTII) genes. After three days of co-cultivation on 2 g/l gellan gum-solidified MS medium containing 100 μM acetosyringone, 30 g/l sucrose, 1 mg/l picloram and different concentrations of MES, they were cultured on the same medium containing 12.5 mg/l meropenem to eliminate Agrobacterium for 2 weeks and then transferred onto medium containing the same concentration of meropenem and 25 mg/l hygromycin for selecting putative transgenic calli. Transient GUS expression was only observed by adding MES to co-cultivation medium. Hygromycin-resistant transgenic calli were obtained only when MES was added to the co-cultivation medium especially at 10 mM. The hygromycin-resistant calli were successfully regenerated into plantlets after transferring onto picloram-free medium. Transformation of plants was confirmed by histochemical GUS assay, PCR analysis and Southern blot analysis.     

Effects of nutrient addition on growth and rhizosphere pH of Leucadendron ‘Safari Sunset’

A greenhouse experiment was conducted to establish the optimal fertilization management for Leucadendron Safari Sunset (Leucadendron salignum × L. laureolum). Addition of NPK and micronutrient fertilizer or raising phosphorus concentration by itself increased total fresh weight and improved plant growth. Elevating the total nutrients or P concentration increased N and P concentrations. Clusters of proteoid roots were present along the root system of plants irrigated with tap-water, whereas few proteoid roots developed on plants irrigated with complete nutrient solution when only P was omitted, and none developed in any of the other treatments with P present.The pH in leachate of plants irrigated with tap water or with high nutrient levels (100, 20 and 100 mg L^-1 of N, P and K, respectively) was consistently lower compared with leachate without plants. Increasing concentration resulted in a significant change in the pH values (pH in leachate with plant – pH in leachate without plant) from negative to positive. This phenomenon is probably related to rhizosphere effects due to plant and microbial activity.     

Effects of High K+ and Alkaline pH on Ultrastructure of Dunaliella salina Chloroplasts

It was reported that the growth of Dunaliella salina Teod. cultured in medium containing 1 mol/L NaC1 was almost completely inhibited by the addition of 100 mmol/L KC1. The high K+ (100 mmol/L KC1) treatment also significantly inhibited the photosynthetic rate of D. salina and decreased chlorophyll contents in algae. This study focuses on possible effects of high K+ or alkaline pH on the ultrastructural change of chloroplasts in D. salina. After D. salina was cultured in a medium containing 100 n,anol/L KC1 or in a medium with alkaline pH for 8 to 10 days, dramatic ultrastructural changes occurred in the chloroplasts including thylakoid swelling, volume increase of chloroplast, and significant accumulation of starch grains in chloroplasts. The results are consistent with our previous report indicating that the ultrastmctuml changes in chloroplast under high K + or alkaline pH may lead to an inhibitory effects on photosynthesis and overall growth of D. salina.     

Effect of Pectin Type on Association and pH Stability of Whey Protein—Pectin Complexes

The purpose of this study was to investigate the influence of pectin type on complex formation between whey protein isolate (WPI) and high methoxy pectins with varying degrees of esterification (DE), and their pH stability. The biopolymer particles with protein-to-polysaccharide mass ratio set to 2:1 were formed at pH 3–7 by heating at 85 °C for 20 min. The particle size, electrical charge, turbidity and microstructure of the biopolymer complexes were evaluated. The optimal conditions for forming WPI-pectin complexes were at the initial pH of 4.5–4.75, just below the isoelectric point of the WPI, where complex formation occurs. At this pH range, the smallest biopolymer complexes (d?=?225–300 nm) could be created. Pectins with 50, 55, 62 and 70 % DE formed relatively small and monomodal complexes with WPI, except for pectin with 71 % DE, which showed major aggregation. The pH stability against aggregation was best with the biopolymer complexes assembled from pectins with 50 % DE (stable at pH 3.5–6.0) and with 62 % DE (stable at pH 3.0–6.0). The results suggest that pectins with varying DE can be used to form small particles and therefore can offer new possibilities in designing novel hierarchical structures and delivery systems.     

Dynamics of planktonic food webs in three mining lakes across a pH gradient (pH 2–4)

Acidic mining lakes (ML) in Lusatia (Germany) are characterised by their geogenically determined chemistry. The present study describes the structure, main components and relationships within the food webs of three acidic mining lakes with different pH values (ML 111: pH 2.6; ML 117: pH 2.8; ML Felix: pH 3.6) in order to show their typical characteristics. The investigation covered the period 1995–1997. The number of species and the biomass are both low, but increase with increasing pH. Planktonic components in the most acidic ML 111 (pH 2.6–2.9) comprise bacteria, Ochromonas spp. and Chlamydomonas spp. and a few rotifers (E. worallii, C. hoodi). Heliozoans are the top-predators. In ML 117 (pH 2.8–3) Gymnodinium sp., ciliates, the rotifer B. sericus and the pioneer crustacean Chydorus sphaericus join the pelagial community. Heliozoans were not found in ML 117 or ML Felix (pH 3.4–3.8). ML Felix had the most taxa. The benthic food chain of all three lakes includes phytobenthic algae as producers, chironomids as primary consumers and corixids as top predators in the profundal. Corixids predate on small cladocerans inhabiting the pelagial in lakes with a pH above 2.8 such as ML Felix. They invade the pelagial and act as a connecting link between the benthic and the pelagic food chains, which are isolated in lakes with a lower pH. Occasionally primary producers and consumers were abundant in all three lakes. These organisms do not depend on the degree of acidity, but on the availability of essential ressources. Mass variations covered up any seasonal variation in the extremely acidic ML 111 (0.9 mm³ l^–1), while in the other two lakes seasonal patterns of biomass were found.     

Treatment of columnaris disease of rainbow trout: low pH and salt as possible tools?

The impact of salt and low pH on columnaris disease of fish was studied. Survival of Flavobacterium columnare after exposure to either 4% NaCl (pH 7.2) or pH 5.0, pH 4.86 or pH 4.6 for 15 min or 1 h was studied in vitro. All conditions significantly reduced the numbers of viable bacterial cells. The effects of salt (4 and 2%) and acidic baths (pH 4.6) were studied in 2 experiments in vivo with rainbow trout Oncorhynchus mykiss infected with F. columnare. Both salt and acidic baths failed to prevent fish mortality; the overall mortality reached 100% in all groups. However, according to survival analysis, the mortality rate was lower in fish treated with 4% salt baths compared to a control group. The buffering capacity of fish skin mucus against low water pH was also studied. Fish skin mucus was an efficient buffer against decreased water pH and the pH of the skin could be remarkably higher than that of the mucus. This may explain the failure of bath treatments to prevent mortality providing that attached F. columnare are located below the mucus surface. We suggest, however, that salt and acidic bath treatments can be used to disinfect water containing F. columnare cells shed by infected fish and thus prevent the transmission of the disease.