卡拉胶和肌原纤维蛋白混合凝胶质构特性的研究

研究卡拉胶和肌原纤维蛋白(MP)浓度比、pH、离子强度和[K+]对混合凝胶质构特性的影响.结果表明:影响混合凝胶硬度和黏着性的主次因素依次为:[K+]、离子强度、浓度比、pH;影响混合凝胶弹性的因素依次为:[K+]、浓度比、pH、离子强度;影响混合凝胶黏聚性的因素依次为:离子强度、[K+]、浓度比、pH.     

The effect of pH on thiosulfate formation in a biotechnological process for the removal of hydrogen sulfide from gas streams

In a biotechnological process for hydrogen sulfide (H2S) removal from gas streams, operating at natronophilic conditions, formation of thiosulfate (S2O3(2-)) is unfavorable, as it leads to a reduced sulfur production. Thiosulfate formation was studied in gas-lift bioreactors, using natronophilic biomass at [Na+] + [K+] = 2 mol L(-1). The results show that at sulfur producing conditions, selectivity for S2O3(2-) formation mainly depends on the equilibrium between free sulfide (HS(-)) and polysulfide (Sx(2-)), which can be controlled via the pH. At pH 8.6, 21% of the total dissolved sulfide is present as Sx(2-) and selectivity for S2O3(2-) formation is 3.9-5.5%. At pH 10, 87% of the total dissolved sulfide is present as Sx(2-) and 20-22% of the supplied H2S is converted to S2O3(2-), independent of the H2S loading rate. Based on results of bioreactor experiments and biomass activity tests, a mechanistic model is proposed to describe the relation between S2O3(2-) formation and pH.     

Speciation of the ionizable antibiotic sulfamethazine on black carbon (biochar)

Adsorption of ionizable compounds by black carbon is poorly characterized. Adsorption of the veterinary antibiotic sulfamethazine (SMT; a.k.a., sulfadimidine; pK(a1) = 2.28, pK(a2) = 7.42) on a charcoal was determined as a function of concentration, pH, inorganic ions, and organic ions and molecules. SMT displayed unconventional adsorption behavior. Despite its hydrophilic nature (log K(ow) = 0.27), the distribution ratio K(d) at pH 5, where SMT(0) prevails, was as high as 10(6) L kg(-1), up to 10(4) times greater than literature reported K(oc). The K(d) decreases at high and low pH but not commensurate with the decline in K(ow) of the ionized forms. At pH 1, where SMT(+) is predominant and the surface is positive, a major driving force is π-π electron donor-acceptor interaction of the protonated aniline ring with the π-electron rich graphene surface, referred to as π(+)-π EDA, rather than ordinary electrostatic cation exchange. In the alkaline region, where SMT(-) prevails and the surface is negative, adsorption is accompanied by near-stoichiometric proton exchange with water, leading to the release of OH(-) and formation of an exceptionally strong H-bond between SMT(0) and a surface carboxylate or phenolate, classified as a negative charge-assisted H-bond, (-)CAHB. At pH 5, SMT(0) adsorption is accompanied by partial proton release and is competitive with trimethylphenylammonium ion, signifying contributions from SMT(+) and/or the zwitterion, SMT(±), which take advantage of π(+)-π EDA interaction and Coulombic attraction to deprotonated surface groups. In essence, both pK(a1) and pK(a2) increase, and SMT(±) is stabilized, in the adsorbed relative to the dissolved state.     

New phenotypes of functional expression of the mKir2.1 channel in potassium efflux-deficient Saccharomyces cerevisiae strains

The functional expression of the mouse Kir2.1 potassium channel in yeast cells lacking transport systems for potassium and sodium efflux (ena1-4delta nha1delta) resulted in increased cell sensitivity to high external concentrations of potassium. The phenotype depended on the level of Kir2.1 expression and on the external pH. The activity of Kir2.1p in the yeast cells was almost negligible at pH 3.0 and the highest at pH 7.0. Kir2.1p was permeable for both potassium and rubidium cations, but neither sodium nor lithium were transported via the channel. Measurements of the cation contents in cells confirmed the higher concentration of potassium in cells with Kir2.1p. Specific inhibition of the mKir2.1 channel activity by Ba2+ cations was observed. The use of a mutant strain lacking both potassium efflux and uptake transporters (ena1-4delta nha1delta trk1delta trk2delta) enabled the monitoring of channel activity on two levels--the provision of the necessary amount of intracellular K+ in media with low potassium concentrations, and simultaneously, the channel's contribution to cell potassium sensitivity in the presence of high external K+. This combination of mutations proved to be a new, sensitive and practical tool for characterizing the properties of heterologously expressed transporters mediating both the efflux and influx of alkali-metal-cations.     

Equilibrium and kinetics of bromine chloride hydrolysis

Aqueous-phase halogen reactions play an important role in tropospheric ozone depletion that is observed during Arctic sunrise where bromine chloride is a key intermediate. The temperature dependencies of BrCl(aq) equilibration with BrCl2-, HOBr(aq), Br2(aq), Cl2(aq), HOCl(aq), Br-, and other species (Br3-, Br2Cl-, Cl3-, OBr-, and OCI-) are determined as a function of Cl- concentration from pH 0 to pH 7. Values for K1 (=[BrCl2-]/([BrCl(aq)][Cl-])) at mu = 1.0 M are 3.8 M(-1) at 25.0 degrees C, 4.7 M(-1) at 10.0 degrees C, and 5.5 M(-1) at 0.0 degrees C, with deltaH1 degrees = -9.9 kJ mol(-1) and deltaS1 degrees = -22 J K(-1) mol(-1). BrCl(aq) hydrolysis equilibria have little or no temperature dependence with Kh1 (=[HOBr(aq)][Cl-][H+]/[BrCl(aq)]) = 1.3 x 10(-4) M2 from 25.0 to 5.0 degrees C, mu = 1.0 M. When conditions are adjusted to give a rapid partial hydrolysis of BrCl in equilibrium with HOBr and Cl- at p[H+] 4.31, a relatively slow reaction (kobsd = 2.4 s(-1)) to form HOCl and Br- is observed. This takes place via BrCl reaction with Cl- to form Cl2, which hydrolyzes in the rate-determining step to give HOCl. On the other hand, the rate of complete BrCl hydrolysis to form HOBr and Cl- at p[H+] 6.4 is extremely rapid with a first-order rate constant of 3.0 x 10(6) s(-1) at 25.0 degrees C. The reverse reaction between HOBr, Cl-, and H+ has a rate constant of 2.3 x 10(10) M(-2) s(-1), so that in seawater, where [Cl-]/[Br-] = 700, the formation of BrCl is much faster than the formation of Br2 from HOBr, Br-, and H+. Rapid formation of BrCl(aq) and its subsequent reaction with Br- is a viable pathway to give Br2(aq). Photolysis of Br2(g) is believed to initiate the reactions associated with ozone depletion.     

Maximizing yellow pigment production in fed-batch culture of Monascus sp

Yellow pigment production in exponential fed-batch cultivation of Monascus sp. was studied. Due to the difficulty of measuring the optical density for accurate determination of the cell concentration, a capacitance probe was employed on-line. The feed rate needed to keep the specific growth rate, mu, constant in fed-batch culture was determined on the basis of the cell concentration measured by the capacitance probe. Control of mu was improved by using updated information on the cell concentration compared with the simple feed-forward determination method using the initial cell concentration only. The highest specific pigment production rate was achieved with a mu of 0.02 h(-1) in the feeding phase. However, among several fermentation examined, the largest pigment production in the final step was obtained at a mu of 0.01 h(-1); in each case the same amount of substrates was used. An investigation of the optimal initial glucose concentration revealed that pigment production was maximum when the initial glucose concentration in the batch mode was 10 g/l and mu was 0.01 h(-1) in the fed-batch mode. It was also found that the pellet weight in the fermentation could be accurately estimated by image analysis. The ratio of the mycelium weight to the total cell weight estimated from information on the total cell weight and the estimated pellet weight was found to be more than 80%. However, no clear quantitative relationship could be discerned between the specific pigment production rate, rho, and the ratio of mycelium in the cell population.     

Temperature dependence of intracellular Ca2+ homeostasis in rat meiotic and postmeiotic spermatogenic cells

The hypothesis that intracellular [Ca2+] is a cell parameter responsive to extreme temperatures in rat meiotic and postmeiotic spermatogenic cells was tested using intracellular fluorescent probes for Ca2+ and pH. In agreement with this hypothesis, extreme temperatures induced a rapid increase of cytosolic [Ca2+] in rat pachytene spermatocytes and round spermatids. Oscillatory changes in temperature can induce oscillations in cytosolic [Ca2+] in these cells. Intracellular [Ca2+] homeostasis in round spermatids was more sensitive to high temperatures compared with pachytene spermatocytes. The calculated activation energies for SERCA ATPase-mediated fluxes in pachytene spermatocytes and round spermatids were 62 and 75 kJ mol(-1), respectively. The activation energies for leak fluxes from intracellular Ca2+ stores were 55 and 68 kJ mol(-1) for pachytene spermatocytes and round spermatids, respectively. Together with changes in cytosolic [Ca2+], round spermatids undergo a decrease in pH(i) at high temperatures. This temperature-induced decrease in pH(i) appears to be partially responsible for the increase in cytosolic [Ca2+] of round spermatids induced by high temperatures. This characteristic of rat meiotic and postmeiotic spermatogenic cells to undergo an increment in cytosolic Ca2+ at temperatures > 33 degrees C can be related to the induction of programmed cell death by high temperatures in these cells.     

耐高酒精野生酵母菌株的筛选及其特性研究

以从内蒙古各旗县果园的果实和土壤中分离得到的200株酵母菌为出发菌株,经四级筛选最终得到一株酒精耐受力为16%vol的菌株K1-2,并对该菌株的发酵特性与生物学特性进行了研究。结果表明,该酵母菌的最适生长pH值为5.5,最适生长温度为28 ℃,最高可耐受600 mg/L的SO2,在葡萄糖含量为60%的条件下仍可生长。发酵5 d后糖醇转化率可达68.45%,产酒精度为6.4%vol,表明该菌株是一株具有良好酒精耐受性与发酵性能的酵母菌株,除拥有较高的耐SO2与耐高糖能力以外,还具备较强的产酒精能力,有很高的应用价值。     

三株野生型耐高温酵母的耐性对比研究

对三株野生型产酒精耐高温马克斯克鲁维酵母(Kluyveromyces marxianus)在不同温度、pH、酒精浓度、糖浓度下的生理耐性进行了研究,并与安琪耐高温酵母进行了比较,得出的结论为:三株野生型耐高温酵母K. marxianus GX-17,K. marxianus HN-79,K.marxianus HN-138高温条件下的生长和产酒精能力明显高于安碘酵母;K marxianus GX-17对pH变化的适应力较安琪酵母强;野生型耐高温酵母的耐糖能力略低于安琪酵母;安琪酵母的耐酒精能力明显高于野生型耐高温酵母.     

Sorption of yttrium and rare earth elements by amorphous ferric hydroxide: influence of temperature

The sorption of yttrium and the rare earth elements (YREEs) by amorphous ferric hydroxide was investigated between 10 and 40 degrees C over a range of pH (4.7-7.1) in the absence of solution complexation. Distribution coefficients, defined as iKFe = [MSi]T/([M]T[Fe3+]s), where [MSi]T is the concentration of sorbed YREEs, [M]T is the total dissolved YREE concentration, and [Fe3+]s is the concentration of precipitated iron, increased with increasing temperature over the entire investigated pH range. The observed increase in iKFe was largest for the heavy REEs, indicating that relative log iKFe values (i.e., YREE patterns) vary somewhat with temperature. The pH dependence of YREE sorption was described by a surface complexation model of the form iKFe = (sbeta1[H+](-1) + sbeta2[H+](-2))/(sK1[H+] + 1), where sbetan are stability constants for sorption of free YREE ions (M3+) and sK1 is a surface protonation constant for amorphous ferric hydroxide. The influence of temperature on the YREE surface stability constants (sbeta1 and sbeta2) was characterized by calculating molar enthalpies for M3+ sorption (deltaH1(0) and deltaH2(0)) using the van 't Hoff equation. The deltaH1(0) values appropriate to sbeta1 range from 11.8 to 13.4 kcal/mol, whereas the deltaH2(0) values appropriate to sbeta2 range between 7.7 and 12.3 kcal/mol. These values are on the same order of magnitude as enthalpies of the first hydrolysis step for a variety of cations.     

The precipitation of proteins by carboxymethyl cellulose.

Carboxymethyl cellulose (CMC) formed insoluble complexes with beta-lactoglobulin, bovine serum albumin and Na caseinate. Maximum precipitation of the beta-lactoglobulin-CMC complex occurred at pH 3-2, whereas maximum precipitation of the bovine serum albumin. The percentage of protein precipitated by CMC decreased with increasing ionic strength of the solution, the rate of decrease being least for bovine serum albumin. At a given ionic strength, more protein was precipitated by CMC of high degree of substitution than by CMC of low degree of substitution. The change in pH (delta pH) occurring on mixing CMC and unbuffered protein solutions, each initially at the same pH, was measured. delta pH was negative for beta-lactoglobulin-CMC mixtures over the pH range 7--2 (minimum at pH 5-5). For bovine serum albumin--Cmc and Na caseinate--CMC mixtures, delta pH was positive between pH 7 and 3-2 (maximum at pH 4-5), zero at pH 3-2 and negative between pH 3-2 and 2-0 (minimum at pH 2-8).     

In situ study of K+ transport into the vacuole of Saccharomyces cerevisiae

Permeable spheroplasts were prepared from two strains of Saccharomyces cerevisiae by incubating with zymolyase without a permeabilizing agent. The loss of the plasma membrane barrier was confirmed by the nucleotide release, the activity of glucose 6-phosphate dehydrogenase with external substrates and by the effects on respiration of mitochondrial substrates and ADP. Mitochondrial integrity was maintained, as shown by respiration with lactate, pyruvate, glucose and ethanol, and its acceleration by ADP showed a coupled respiration. Potassium uptake into the vacuole was measured with a selective electrode and found to be taken up effectively by spheroplasts only in the presence of Mg-ATP; it was reverted by CCCP and PCP and inhibited by bafilomycin A1, but not by sodium vanadate or sodium azide. Potassium ions did not alter DeltaPsi of the vacuole, followed with oxonol V, but caused vacuolar alkalinization, as followed with pyranine. The increase of vacuolar pH was non-selective and observed at 50-200 mM of several monovalent cations. Isolated vacuoles with pyranine inside showed similar changes of the internal pH in the presence of KCl. Results indicate that some strains do not require a permeabilizing agent to directly access the vacuole in spheroplasts prepared with zymolyase. The hypothesis about the existence of a K+/H+ antiporter in the vacuolar membrane of S. cerevisiae is discussed.     

Dynamics of intracellular calcium induced by lactate and glucose in rat pachytene spermatocytes and round spermatids

Glycolytic metabolism in meiotic and post-meiotic spermatogenic cells shows differentiation-related changes. The developmental and physiological significance of these metabolic changes is not known. The aim of the present study was to test the hypothesis that glucose and lactate metabolism can modulate intracellular calcium [Ca2+](i) in spermatogenic cells in an opposing and dynamic manner. Fluorescent probes were used to measure [Ca2+](i) and pH(i), and HPLC was used to measure intracellular adenine nucleotides and mitochondrial sensing of ATP turnover. [Ca2+](i) in pachytene spermatocytes and round spermatids was modulated by changes in lactate and glucose concentrations in the media. The kinetics and magnitude of the [Ca2+](i) changes induced by lactate and glucose were different in meiotic and post-meiotic spermatogenic cells. The presence of glucose in the medium induced a decrease in pH(i) in spermatogenic cells. This glucose-induced pH(i) decrease occurred later than the changes in [Ca2+](i), which were also observed when the pH(i) decrease was inhibited, indicating that the glucose-induced [Ca2+](i) increase was not a consequence of pH(i) changes. Hexose phosphorylation in glycolysis was part of the mechanism by which glucose metabolism induced a [Ca2+](i) increase in spermatogenic cells. The sensitivity of [Ca2+](i) to carbohydrate metabolism was higher in round spermatids than in pachytene spermatocytes. Thus, differentiation-related changes in carbohydrate metabolism in spermatogenic cells determine a dynamic and differential modulation of their [Ca2+](i) by glucose and lactate, two substrates secreted by the Sertoli cells.     

添加辅酶前体及流加诱导物提高黄嘌呤氧化酶发酵产率

通过对产黄嘌呤氧化酶菌株进行16S rDNA序列分析,构建系统进化树,确定该菌株为球形节杆菌(Arthrobacter globiformis)。添加辅酶前体(核黄素、硫胺素)及诱导物(次黄嘌呤,3.6 g/L),提高了发酵产酶;通过两种方式流加葡萄糖及次黄嘌呤,结果表明,发酵至24 h,一次性补葡萄糖质量浓度4.0 g/L,流加次黄嘌呤质量浓度至3.6 g/L,酶产率可达8 952.7 U/L,比未补料时提高25.7%,平均产率系数达1 041.0 U/g。测定流加发酵过程中铵根离子浓度变化,发现一定质量浓度的铵根离子抑制发酵产黄嘌呤氧化酶。     

Mode of action of lactocin 705, a two-component bacteriocin from Lactobacillus casei CRL705

Lactocin 705 is a bacteriocin whose activity depends on the complementary action of two peptides (705alpha and 705beta) of 33-amino-acid residues each and is produced by Lactobacillus casei CRL705. Biologically active, synthetic lactocin 705 was used to study the mode of action on sensitive cells of Lactobacillus plantarum CRL691. The addition of 90 nmol l(-1) of lactocin 705 to cells of L. plantarum dissipated both, the membrane potential (DeltaPsi) and the pH gradient (DeltapH). Energized membrane, obtained after the addition of glucose, were more susceptible to lactocin 705 action leading to the immediate release of intracellular K(+) and inorganic phosphate. When the role of various ions on sensitive cells were analyzed, only Ca(2+) ion exhibited a protective effect against lactocin 705. These data suggest that the presence of a proton motive force (PMF) promotes the interaction of the bacteriocin with the cytoplasmic membrane of energized cells, leading to pore formation which allows for the efflux of ions, thereby ensuring efficient killing of target bacteria.     

The effect of temperature and pH on the growth of lactic acid bacteria: a pH-auxostat study

The growth of Streptococcus salivarius subsp. thermophilus, Lactococcus lactis subsp. lactis, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus and Lactobacillus paracasei was studied in a pH-auxostat. The computer-controlled smooth change of pH or temperature was used to study the effect of pH and temperature on the culture characteristics (specific growth rate mu growth yield Y(ATP) and specific lactate production rate Q(ATP)). The behaviour of mu and Q(ATP) with an increase of temperature suggested that ATP production capacity was an important factor in determining the maximum growth rate of lactic acid bacteria (LAB). The decrease of Y(ATP) with increase of temperature resulted in the decrease of specific growth rate while Q(ATP) remained constant or even increased. With the decrease of pH, decrease of both Y(ATP) and Q(ATP) was observed. S. thermophilus St20 having the highest maximum specific growth rate of 2.2 h(-1) at 44 degrees C was the most acid sensitive strain. The L. paracasei E1H3 having the lowest mu(max) was the most tolerant strain to pH change. The behaviour of mixed culture of L. bulgaricus and S. thermophilus in milk in a pH-auxostat with pH-decrease was in agreement with the pure culture experiments of the same species. The study showed that pH-auxostat with smooth controlled change of pH and temperature is an effective method for determination of technological characteristics and comparative physiological study of LAB.     

Enhanced 2,3-butanediol production by addition of acetic acid in Paenibacillus polymyxa

By the addition of 150 mM acetate into a batch culture at an initial pH of 6.8, the production of 2,3-butanediol (BDL) by Paenibacillus polymyxa reached 248 mM, yielding 0.87 mol.mol(-1) glucose, where the ratio of acetate consumed to glucose consumed (A/C ratio) was calculated as 0.35 mol acetate mol(-1) glucose. Therefore, a fed-batch culture was carried out by feeding glucose and acetate at a ratio of 0.35 mol acetate mol(-1) glucose. In the fed-batch culture performed at pH 6.8, BDL production reached 637 mM, yielding 0.81 mol.mol(-1) glucose, although the A/C ratio was only 0.18 mol acetate mol(-1) glucose. By decreasing pH to 6.3 in the fed-batch culture, BDL production reached 566 mM, yielding 0.88 mol.mol(-1) glucose and the A/C ratio was 0.32 mol acetate mol(-1) glucose. The optical purity of BDL, which was expressed as enantiomeric excess, was retained at more than 98% of the (R, R)-stereoisomer at the end of culture, which was comparable to that without acetate addition.     

Binding constants of divalent mercury (Hg2+) in soil humic acids and soil organic matter

Distribution coefficients (K(OC)) for Hg2+ binding by IHSS Pahokee peat humic acid (PHA) and humic acids separated from O-horizons and peats in a northern temperate forest were determined using a competitive ligand-exchange method. All measurements were made at low ratios of added Hg2+ to reduced S. The commonly used chelating agents, EGTA and DTPA, were found to be ineffective competitive ligands; thus, we used DL-penicillamine, a synthetic amino acid with a thiol group. Calculated free [Hg2+] at equilibrium is very low, ranging from 10(-26.4) at pH 1.9 to 10(-36.9) at pH 5.8. Corresponding log Koc values ranged from 22.6 to 32.8. The slope of the plot of pH versus log K(OC) was 2.68, suggesting that two or more protons are released when each Hg2+ is bound. This is consistent with binding of Hg2+ to bidentate thiol sites with some participation of a third weak-acid group, presumably a thiol. The 1:2 stoichiometry is consistent with X-ray spectroscopy data for Hg2+ bound to HA and with other pH-dependency results showing release of two protons with the binding of each Hg2+. Our K(OC) values are much greater than indicated by the data from most previous studies.     

Hypoxanthine Ratio Determination in Fish Extract Using Capillary Electrophoresis and Immobilized Enzymes

Fish freshness was assessed using capillary electrophoresis and an immobilized enzyme procedure to monitor degradation of inosine-5′-monophosphate (IMP), inosine (HxR) and hypoxanthine (Hx). The enzymatic method used an amperometric probe at + 0.7 V (platinum vs silver/silver chloride) with immobilized xanthine oxidase, catalase, nucleoside phosphorylase, and nucleotidase for converting Hx, HxR or IMP to uric acid. Capillary electrophoresis resolved IMP, inosine and Hx by migration rates resulting from an applied electric field (416 V/cm, 50 μA). Components were detected at 250 nm. The H ratio of Hx/[IMP + HxR + Hx] and simplified K value of [HxR + Hx]/ [IMP + HxR + Hx] were determined in cod, salmon and trout stored on ice (0-4°C) and at 20°C. The two procedures agreed and for all species H ratio and K values increased with storage time.