Effects of arbuscular mycorrhizal fungal species and the medium pH on the growth of Pueraria phaseoloides (Roxb.) Benth

Soil conditions may change the response of plants to inoculation with arbuscular mycorrhizal fungi (AMF). This, in turn, may influence the development of mycorrhizal associations. The effect of AM species isolated from different ecosystems was evaluated on Pueraria phaseoloides (kudzu). Experiments were conducted under controlled conditions in Leonard jars, on a substrate made of peat, rice husk, and vermiculite (1-1-1) enriched with rock phosphate plus a modified Hoagland nutrient solution. In the first experiment the initial pH of the substrate (8.0) was reduced by approximately one unit by inoculation with Kuklospora colombiana, Glomus clarum, and Glomus manihotis. The result was the same for Acaulospora longula species when 4-morpholine ethanesulphonic acid (MES) buffer was used. The final pH of the substrate was correlated with the above-ground plant biomass production suggesting that the most effective fungus regulated the pH of the substrate. This positive interaction leads to a higher concentration of P and K in plants. When the pH of the substrate was buffered with MES, in the second experiment, the efficiency of K. colombiana was reduced, even though plants inoculated with this fungus yielded more than non-inoculated plants. G. intraradices and A. longula were favoured by buffer addition. Beneficial buffer effects on this plant resulted in lower pH, better plant P and K uptake, and higher biomass production. The best plant yield was obtained at pH 7.0 in both experiments. G. clarum and G. manihotis yielded the highest biomass production. Under the proposed conditions, AMF improved P. phaseoloides growth and pH regulation. These growth conditions may be used for the evaluation and propagation of some AMF species adding MES buffer in the nutrient solution.     

Microrespirometric characterization of activated sludge inhibition by copper and zinc

We have developed a novel microrespirometric method to characterize the inhibitory effects due to heavy metals on activated sludge treatment. This method was based on pulse dynamic respirometry and involved the injection of several pulses of substrate and inhibitors, of increasing concentration. Furthermore, we evaluated the inhibitory effects of heavy metals (copper and zinc), substrate and biomass concentrations, and pH on activated sludge activity. While higher biomass concentrations counteracted the inhibitory effects of both copper and zinc, higher substrate concentrations predominantly augmented the inhibitory effect of copper but no significant change in inhibition by zinc was observed. pH had a clear but relatively small effect on inhibition, partially explained by thermodynamic speciation. We determined the key kinetic parameters; namely, the half saturation constant (K _S ) and the maximum oxygen uptake rate (OUR _max ). The results showed that higher heavy metal concentrations substantially decreased K _S and OUR _max suggesting that the inhibition was uncompetitive.     

Some properties of a ficin-papain inhibitor from avian egg white

A procedure has been established for the isolation, from sheep liver, of 6-phosphogluconate dehydrogenase which is homogeneous according to the criteria of the analytical ultracentrifuge, and isoelectric focusing. A systematic determination of the effects of pH, ionic strength, metal ions, and temperature, on the kinetic parameters of the isolated 6-phosphogluconate dehydrogenase has been carried out. Double-reciprocal plots of enzyme rate measurements as a function of substrate concentration indicate K_m values of 15 μm for 6-phosphogluconate, and 7 μm for NADP⁺, under optimum assay conditions, and show no effect of the concentration of one substrate on the K_m of the other substrate under the assay conditions employed. Ionic strength, monovalent and divalent metals, are apparently interchangeable in their ability to activate the enzyme, and act by decreasing the K_m values of the enzyme, not by increasing the reaction rate. Concentrations of metals above the optimum are strongly inhibitory. Plots of ?log K_m vs pH show inflection points at 8.3 for 6-phosphogluconate, and 6.5 for NADP⁺. At low substrate concentrations the pH optimum of the enzyme is at pH 7.7, but plots of V vs pH increase up to pH 9.1 (the enzyme is unstable at higher pH values). An Arrhenius plot shows a straight line between temperatures of 8.6 and 39.4 °C, and an energy of activation of 15,450 cal mole^?1.     

Identification of cathepsin B,D and H in the larval midgut of colorado potato beetle,Leptinotarsa decemlineata say (Coleoptera: Chrysomelidae)

The larval midgut of the Colorado beetle, Leptinotarsa decemlineata contains cathepsin B, D and H activity detected by use of haemoglobin, synthetic substrates specific for each enzyme, pH at which the substrate was maximally hydrolysed and effects of potential activators and inhibitors on proteolytic activity. Cysteine proteases cathepsin B, and H were activated by thiol compounds and inhibited by iodoacetamide, TLCK and epoxysuccinyl-leucyl-amido(guanidino)butane (E-64) a cysteine specific proteinase inhibitor. Cathepsin B was distinguished from H by hydrolysis of benzoyloxycarbonyl-Ala-Arg-Arg-methoxynaphthylamide, a cathepsin B specific substrate and inhibition of substrate hydrolysis by leupeptin. Cathepsin H activity, detected using the specific substrate arginine-naphthylamide, was insensitive to leupeptin. Cathepsin D had maximal activity at pH 4.5 and was inhibited by pepstatin, an aspartic proteinase inhibitor.     

Sugar Transport into Protoplasts Isolated from Developing Soybean Cotyledons : II. Sucrose Transport Kinetics, Selectivity, and Modeling Studies

The effects of metabolic inhibitors, pH, and temperature on the kinetics of sucrose uptake protoplasts isolated from developing soybean Glycine max L. cv Wye cotyledons were studied. Structural requirements for substrate recognition by the sucrose carrier were examined by observing the effects of potential alternate substrates for the saturable component on sucrose uptake.     

Substrate activation in acetylcholinesterase induced by low pH or mutation in the π-cation subsite

Substrate inhibition is considered a defining property of acetylcholinesterase (AChE), whereas substrate activation is characteristic of butyrylcholinesterase (BuChE). To understand the mechanism of substrate inhibition, the pH dependence of acetylthiocholine hydrolysis by AChE was studied between pH 5 and 8. Wild-type human AChE and its mutants Y337G and Y337W, as well as wild-type Bungarus fasciatus AChE and its mutants Y333G, Y333A and Y333W were studied. The pH profile results were unexpected. Instead of substrate inhibition, wild-type AChE and all mutants showed substrate activation at low pH. At high pH, there was substrate inhibition for wild-type AChE and for the mutant with tryptophan in the π-cation subsite, but substrate activation for mutants containing small residues, glycine or alanine. This is particularly apparent in the B. fasciatus AChE. Thus a single amino acid substitution in the π-cation site, from the aromatic tyrosine of B. fasciatus AChE to the alanine of BuChE, caused AChE to behave like BuChE. Excess substrate binds to the peripheral anionic site (PAS) of AChE. The finding that AChE is activated by excess substrate supports the idea that binding of a second substrate molecule to the PAS induces a conformational change that reorganizes the active site.     

Kinetic characterization of gyroxin,a serine protease from Crotalus durissus terrificus venom

This work describes for the first time the characterization of the enzymatic features of gyroxin, a serine protease from Crotalus durissus terrificus venom, capable to induce barrel rotation syndrome in rodents. Measuring the hydrolysis of the substrate ZFR-MCA, the optimal pH for proteolytic cleavage of gyroxin was found to be at pH 8.4. Increases in the hydrolytic activity were observed at temperatures from 25 °C to 45 °C, and increases of NaCl concentration up to 1 M led to activity decreases. The preference of gyroxin for Arg residues at the substrate P1 position was also demonstrated. Taken together, this work describes the characterization of substrate specificity of gyroxin, as well as the effects of salt and pH on its enzymatic activity.     

Enzymatic Saccharification of Lignocelluloses Should be Conducted at Elevated pH 5.2–6.2

This study revealed that cellulose enzymatic saccharification response curves of lignocellulosic substrates were very different from those of pure cellulosic substrates in terms of optimal pH and pH operating window. The maximal enzymatic cellulose saccharification of lignocellulosic substrates occurs at substrate suspension pH 5.2–6.2, not between pH 4.8 and 5.0 as exclusively used in literature using T. reesi cellulase. Two commercial cellulase enzyme cocktails, Celluclast 1.5L and CTec2 both from Novozymes, were evaluated over a wide range of pH. The optimal ranges of measured suspension pH of 5.2–5.7 for Celluclast 1.5L and 5.5–6.2 for CTec2 were obtained using six lignocellulosic substrates produced by dilute acid, alkaline, and two sulfite pretreatments to overcome recalcitrance of lignocelluloses (SPORL) pretreatments using both a softwood and a hardwood. Furthermore, cellulose saccharification efficiency of a SPORL-pretreated lodgepole pine substrate showed a very steep increase between pH 4.7 and 5.2. Saccharification efficiency can be increased by 80 % at cellulase loading of 11.3 FPU/g glucan, i.e., from approximately 43 to 78 % simply by increasing the substrate suspension pH from 4.7 to 5.2 (buffer solution pH from 4.8 to 5.5) using Celluclast 1.5L, or by 70 % from approximately 51 to 87 % when substrate suspension pH is increased from 4.9 to 6.2 (buffer solution pH from 5.0 to 6.5) using CTec2. The enzymatic cellulose saccharification response to pH is correlated to the degree of substrate lignin sulfonation. The difference in pH-induced lignin surface charge, and therefore surface hydrophilicity and lignin–cellulase electrostatic interactions, among different substrates with different lignin content and structure is responsible for the reported different enhancements in lignocellulose saccharification at elevated pH.     

Screening of microbes for novel acidic cutinases and cloning and expression of an acidic cutinase from Aspergillus niger CBS 513.88

Isolates from gardening waste compost and 38 culture collection microbes were grown on agar plates at pH 4.0 with the cutinase model substrate polycaprolactone as a carbon source. The strains showing polycaprolactone hydrolysis were cultivated in liquid at acidic pH and the cultivations were monitored by assaying the p-nitrophenyl butyrate esterase activities. Culture supernatants of four strains were analyzed for the hydrolysis of tritiated apple cutin at different pHs. Highest amounts of radioactive hydrolysis products were detected at pHs below 5. The hydrolysis of apple cutin by the culture supernatants at acidic pH was further confirmed by GC–MS analysis of the hydrolysis products. On the basis of screening, the acidic cutinase from Aspergillus niger CBS 513.88 was chosen for heterogeneous production in Pichia pastoris and for analysis of the effects of pH on activity and stability. The recombinant enzyme showed activity over a broad range of pHs with maximal activity between pH 5.0 and 6.5. Activity could be detected still at pH 3.5.     

Influence of solid substrate fermentation on the chemical composition of chickpea

A basic procedure was developed to produce a fermented product by solid substrate fermentation using Rhyzopus oligosporus and chickpea as substrate. Water activity was kept at 0.92 throughout the process. Fermentation increased total, ‘true’ and soluble proteins, soluble solids and soluble carbohydrates, and decreased fiber content and pH. About 12% of solids were lost during 72 h of fermentation. The content of most fatty acids was enhanced by fermentation, whereas peroxide value and tannins declined. The color of the fermented product was not deteriorated after 72 h of fermentation. Scanning electron microscopy studies of microbial growth on the substrate showed penetration of the fungus hyphae and degradation effects on the chickpea cotyledon cells.     

Properties of a Membrane-bound Phosphatase from the Thylakoids of Spinach Chloroplasts

A 3-phosphoglycerate phosphatase activity of about 2 micromoles per minute per milligram chlorophyll is associated with the thylakoid membranes of spinach chloroplasts. The K_m for 3-phosphoglycerate is 3 millimolar. The enzyme can be solubilized from thylakoid membranes by treatment with 0.33 molar MgCl₂ or sodium deoxycholate. The activity is not stimulated by sulfhydryl reagents or the addition of 10 millimolar MgCl₂. The enzymic activity is insensitive to ethylenediaminetetraacetate. The pH optimum is broad, between 5.5 to 7.5. Although the substrate specificity is broad, 3-phosphoglycerate is the best substrate of those tested at neutral pH. However, p-nitrophenyl phosphate was a more effective substrate at pH 5.5. The enzyme exhibits the general characteristics of an acid phosphatase.     

Comparative studies on soluble and immobilized yeast hexokinase

Comparative studies have been carried out on soluble and immobilized yeast hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1). The enzyme was immobilized by covalent attachment to a polyacrylamide type support containing carboxylic functional groups. The effects of immobilization on the catalytic properties and stability of hexokinase were studied. As a result of immobilization, the pH optimum for catalytic activity was shifted in the alkaline direction to ～pH 9.7. The apparent optimum temperature of the immobilized enzyme was higher than that of the soluble enzyme. The apparent K_m value with D-glucose as substrate increased, while that with ATP as substrate decreased, compared with the data for the soluble enzyme. Differences were found in the thermal inactivation processes and stabilities of the soluble and immobilized enzymes. The resistance to urea of the soluble enzyme was higher at alkaline pH values, while that for the immobilized enzyme was greatest at ～pH 6.0.     

Regulation of the reconstituted chloroplast phosphate translocator by an H+ gradient

This report describes the influence of ΔpH on the transport of phosphate, triose phosphate and 3-phosphoglycerate catalyzed by the phosphate translocator in a reconstituted system. The H⁺ gradient across the liposome membrane is adjusted by the addition of external buffer solution and maintained for several minutes. The following results are obtained: (1) An inward directed H⁺ gradient leads to an increase of 3-phosphoglycerate transport and to a decrease of phosphate and triose phosphate transport. (2) An H⁺ gradient in the opposite direction results in a restriction of 3-phosphoglycerate influx whereas the influx of phosphate and triose phosphate is enhanced. (3) The magnitude of the pH effect depends on the internal substrate. Compared to the homoexchange mode, the effect of applied ΔpH is more pronounced in the heteroexchange mode. (4) Transport of phosphate and 3-phosphoglycerate is influenced by ΔpH in a different manner. In the case of phosphate and triose phosphate transport the observed effects are associated with changes in the apparent K_m values whereas in the case of 3-phosphoglycerate transport the application of a pH gradient is linked to a change of V_max. (5) In competition experiments with both substrates in the external medium, ΔpH influences the effect of phosphate as a competitive inhibitor of 3-phosphoglycerate transport whereas the effect of 3-phosphoglycerate on phosphate transport is not affected by a pH gradient. (6) The measured apparent K_m and V_max values under the influence of ΔpH can be used for the calculation of substrate fluxes across the envelope during illumination. It can be demonstrated that the increase of stromal pH in the light gives rise to a considerable change in the ratio of the substrates transported. Under conditions without pH gradient, the species transported out is mainly 3-phosphoglycerate and the species transported in is mainly triose phosphate. These fluxes are reversed when a pH gradient is applied (light conditions).     

Production of a collagenase from Candida albicans URM3622

Culture conditions (pH, time, temperature, inoculum size, orbital agitation speed and substrate concentration) for an extracellular collagenase produced by Candida albicans URM3622 were studied using three experimental designs (one 2⁶⁻² fractionary factorial and two 2³ full factorial). The analysis of the 2⁶⁻² fractionary design data indicated that agitation speed and substrate concentration had the most significant effect on collagenase production. Based on these results, two successive 2³ full factorial design experiments were run in which the effects of substrate concentration, orbital agitation speed and pH were further studied. These two sets of experiments showed that all variables chosen were significant for the enzyme production, with the maximum collagenolytic activity of 6.8 ± 0.4 U achieved at pH 7.0 with an orbital agitation speed of 160 rpm and 2% substrate concentration. Maximum collagenolytic activity was observed at pH 8.2 and 45 °C. The collagenase was stable within a pH range of 7.2–8.2 and over a temperature range of 28–45 °C. These results clearly indicate that C. albicans URM3622 is a potential resource for collagenase production and could be of interest for pharmaceutical, cosmetic and food industry.     

Activation of aspartase by glycerol

Aspartase [EC 4.3.1.1] of Escherichia coli, which exhibits a sigmoidicity in the substrate saturation profile at alkaline pH, was markedly activated by 10–20% glycerol at low substrate concentrations and pH 8.5. In contrast, no activation, but an inhibition was observed at pH 7.0 throughout the substrate concentrations tested. The activation profile of the enzyme as a function of glycerol concentration was considerably influenced by L-aspartate concentration. Neither alteration of the cooperative nature of the enzyme nor subunit dissociation was associated with the activation. Besides glycerol, ethylene glycol, propylene glycol, dimethylsulfoxide, and dioxane also activated the enzyme.     

Isolation and examination of thioglucoside glucohydrolase from seeds of Brassica napus

Thioglucoside glucohydrolase (EC 3.2.3.1) was extracted from seeds of Brassica napus cv. panter (rape) and purified by a procedure including gel filtration and ion exchange chromatography. Its specific activity using allylglucosinolate as substrate was more than twice that when using 2-hydroxybut-3-enylglucosinolate, even though the latter glucosinolate is the natural substrate in B. napus. At least two isoenzymes were detected with pH optima of 4.4 and 8.0. 5-Vinyloxazolidine-2-thione was the sole product of enzymic degradation of 2-hydroxybut-3-enylglucosinolate above pH 5.4 reaching a maximum at pH 8.0, whilst 1-cyano-2-hydroxybut-3-ene was the main product at low pH reaching a maximum at 3.4.     

K stimulation of ATPase activity associated with the chloroplast inner envelope

Studies were conducted to characterize ATPase activity associated with purified chloroplast inner envelope preparations from spinach (Spinacea oleracea L.) plants. Comparison of free Mg²⁺ and Mg·ATP complex effects on ATPase activity revealed that any Mg²⁺ stimulation of activity was likely a function of the use of the Mg·ATP complex as a substrate by the enzyme; free Mg²⁺ may be inhibitory. In contrast, a marked (one- to twofold) stimulation of ATPase activity was noted in the presence of K⁺. This stimulation had a pH optimum of approximately pH 8.0, the same pH optimum found for enzyme activity in the absence of K⁺. K⁺ stimulation of enzyme activity did not follow simple Michaelis-Menton kinetics. Rather, K⁺ effects were consistent with a negative cooperativity-type binding of the cation to the enzyme, with the K_m increasing at increasing substrate. Of the total ATPase activity associated with the chloroplast inner envelope, the K⁺-stimulated component was most sensitive to the inhibitors oligomycin and vanadate. It was concluded that K⁺ effects on this chloroplast envelope ATPase were similar to this cation's effects on other transport ATPases (such as the plasmalemma H⁺-ATPase). Such ATPases are thought to be indirectly involved in active K⁺ uptake, which can be facilitated by ATPase-dependent generation of an electrical driving force. Thus, K⁺ effects on the chloroplast enzyme in vitro were found to be consistent with the hypothesized role of this envelope ATPase in facilitating active cation transport in vivo.     

Involvement of Histidine Residue His382 in pH Regulation of MCT4 Activity

Monocarboxylate transporter 4 (MCT4) is a pH-dependent bi-directional lactate transporter. Transport of lactate via MCT4 is increased by extracellular acidification. We investigated the critical histidine residue involved in pH regulation of MCT4 function. Transport of lactate via MCT4 was measured by using a Xenopus laevis oocyte expression system. MCT4-mediated lactate transport was inhibited by Zn²⁺ in a pH physiological condition but not in an acidic condition. The histidine modifier DEPC (diethyl pyrocarbonate) reduced MCT4 activity but did not completely inactivate MCT4. After treatment with DEPC, pH regulation of MCT4 function was completely knocked out. Inhibitory effects of DEPC were reversed by hydroxylamine and suppressed in the presence of excess lactate and Zn²⁺. Therefore, we performed an experiment in which the extracellular histidine residue was replaced with alanine. Consequently, the pH regulation of MCT4-H382A function was also knocked out. Our findings demonstrate that the histidine residue His382 in the extracellular loop of the transporter is essential for pH regulation of MCT4-mediated substrate transport activity.     

西藏色季拉山高山倭蛙的产卵地选择

高山倭蛙(Nanorana parkeri)是青藏高原的特有种和广布种.2011 ～2012年,在西藏色季拉山高山倭蛙的繁殖期内对其产卵地选择进行了调查.测量分析了产卵地及对照样方的10个环境变量后,发现高山倭蛙的产卵地与对照样方在底质、pH、水温、水深、植被盖度和有无鱼方面有显著差异,回归分析表明底质特点和pH是影响高山倭蛙产卵地选择的最主要因素.今后在该物种的保护工作中,应加强对湿地中底质为泥、pH偏中性水体的保护.