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In the chloroplast stroma, dynamic pH changes occur from acidic to alkaline in response to fluctuating light conditions. We investigated the pH dependency of the electron transfer reaction of ferredoxin-NADP+ reductase (FNR) with ferredoxin (Fd) isoproteins, Fd1 and Fd2, which are localized in mesophyll cells and bundle sheath cells, respectively, in the leaves of C4 plant maize. The pH-dependent profile of the electron transfer activity with FNR was quite different between Fd1 and Fd2, which was mainly explained by the opposite pH dependency of the Km value of these Fds for FNR. Replacement of the amino acid residue at position of 65 (D65N) and 78 (H78A) between the two Fds conferred different effect on their pH dependency of the Km value. Double mutations of the two residues between Fd1 and Fd2 (Fd1D65N/H78A and Fd2N65D/A78H) led to the mutual exchange of the pH dependency of the electron transfer activity. This exchange was mainly explained by the changes in the pH-dependent profile of the Km values. Therefore, the differences in Asp/Asn at position 65 and His/Ala at position 78 between Fd1 and Fd2 were shown to be the major determinants for their different pH dependency in the electron transfer reaction with FNR.

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Monoclonal antibodies (mAbs) as therapeutics necessitate favorable pharmacokinetic properties, including extended serum half-life, achieved through pH-dependent binding to the neonatal Fc receptor (FcRn). While prior research has mainly investigated IgG-FcRn binding kinetics with a focus on single affinity values, it has been shown that each IgG molecule can engage two FcRn molecules throughout an endosomal pH gradient. As such, we present here a more comprehensive analysis of these interactions with an emphasis on both affinity and avidity by taking advantage of switchSENSE technology, a surface-based biosensor where recombinant FcRn was immobilized via short DNA nanolevers, mimicking the membranous orientation of the receptor. The results revealed insight into the avidity-to-affinity relationship, where assessing binding through a pH gradient ranging from pH 5.8 to 7.4 showed that the half-life extended IgG1-YTE has an affinity inflection point at pH 7.2, reflecting its engineering for improved FcRn binding compared with the wild-type counterpart. Furthermore, IgG1-YTE displayed a pH switch for the avidity enhancement factor at pH 6.2, reflecting strong receptor binding to both sides of the YTE-containing Fc, while avidity was abolished at pH 7.4. When compared with classical surface plasmon resonance (SPR) technology and complementary methods, the use of switchSENSE demonstrated superior capabilities in differentiating affinity from avidity within a single measurement. Thus, the methodology provides reliable kinetic rate parameters for both binding modes and their direct relationship as a function of pH. Also, it deciphers the potential effect of the variable Fab arms on FcRn binding, in which SPR has limitations. Our study offers guidance for how FcRn binding properties can be studied for IgG engineering strategies.

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The pressing challenge of cancer's high mortality and invasiveness demands improved therapeutic approaches. Targeting the nutrient dependencies within cancer cells has emerged as a promising approach. This study is dedicated to demonstrating the potential of arginine depletion for cancer treatment. Notably, the focus centers on arginine decarboxylase (RDC), a pH-dependent enzyme expecting enhanced activity within the slightly acidic microenvironments of tumors. To investigate the effect of a single-site mutation on the catalytic efficacy of RDC, diverse amino acids, including glycine, alanine, phenylalanine, tyrosine, tryptophan, p-azido-phenylalanine, and a phenylalanine analog with a hydrogen-substituted tetrazine, were introduced at the crucial threonine site (position 39) in the multimer-forming interface. Remarkably, the introduction of either a natural or a non-natural aromatic amino acid at position 39 substantially boosted enzymatic activity, while amino acids with smaller side chains did not show the same effect. This enhanced enzymatic activity is likely attributed to the reinforced formation of multimer structures through favorable interactions between the introduced aromatic amino acid and the neighboring subunit. Noteworthy, at slightly acidic pH, the RDC variant featuring tryptophan at position 39 demonstrated augmented cytotoxicity against tumor cells compared to the wild-type RDC. This attribute aligns with the tumor microenvironment and positions these variants as potential candidates for targeted cancer therapy.

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The method of soil improvement by calcium phosphate precipitation is a novel, environmentally friendly, and non-toxic technique. Such technology provides advantages over ureolytic induced calcite precipitation (UICP), the most popular and widely used method in the field of geotechnical engineering. In this paper, an investigation of the consolidation of fine and coarse sand samples by enzyme induced calcium phosphate precipitation (EICPP) was carried out. Tuna bones were used as an alternative source of calcium and phosphorus ions, as one of the most popular fish species in Japan and the main source of food industry waste. Unconfined compressive strength (UCS) of the samples after 21 days of daily injection of the solution showed an increase in strength up to 6,05 MPa in fine and up to 4,3 MPa in coarse sand samples. X-ray powder diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (SEM-EDS) analysis were performed to investigate the nature and type of deposition. Analyses confirmed that deposition is composed of brushite with needle-like crystals in the case of Toyoura sand and flower-like crystals in the case of Mikawa sand. SEM-EDS showed a presence of both, calcium, and phosphorus in the precipitate, indicating the presence of calcium phosphate compounds (CPCs). This study reveals that tuna bones are a rich source of calcium and phosphorus for EICPP, which results in a strengthening of silicate soil up to 3.4-6.05 MPa and is able to reduce ammonia emissions by 85.7 % - 97.5 % compared to UICP.

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In this work, the hydroxylation mechanisms and kinetics of some emerging disinfection byproducts (DBPs) have been systematically investigated through theoretical calculation methods. Five chlorophenols and eleven halogenated pyridinols were chosen as the model compounds to study their pH-dependent reaction laws in UV/H2O2 system. For the reactions of HO• with 37 different dissociation forms, radical adduct formation (RAF) was the main reaction pathway, and the reactivity decreased with the increase of halogenation degree. The kapp values (at 298 K) increased with the increase of pH from 0 to 10, and decreased with the increase of pH from 10 to 14. Compared with phenol, the larger the chlorination degree in chlorophenols was, the stronger the pH sensitivity of the kapp values; compared with chlorophenols, the pH sensitivity in halogenated pyridinols was further enhanced. As the pH increased from 2 to 10.5, the degradation efficiency increased at first and then decreased. With the increase of halogenation degree, the degradation efficiency range increased, the pH sensitivity increased, the optimal degradation efficiency slightly increased, and the optimal degradation pH value decreased. The ecotoxicity and bioaccumulation of most hydroxylated products were lower than their parental compounds. These findings provided meaningful insights into the strong pH-dependent hydroxylation of emerging DBPs on molecular level.

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Plant proteins are constantly gaining attention as potential substitutes for dairy proteins, due to their suitable functionality and nutritional value. This study was designed to compare the structural and functional responses of different plant protein isolates (soy, pea, lentil, and chickpea) with two commonly used dairy protein (whey protein isolates and sodium caseinate) under different pH treatments (pH 3.0, 5.0, 7.0, and 9.0). The results showed that pH had a different alteration on the structural, surface properties and functional properties of plant and dairy proteins. Plant protein generally possessed a darker color, lower solubility, emulsifying properties, and foaming capacity, whereas their foaming stability and water holding capacity were higher than those of dairy proteins. Soy protein isolates were characterized by its comparable proportion of ß-turn and random coils, zeta-potential, emulsifying (30.37 m2/g), and water-holding capacity (9.03 g/g) at alkaline conditions and chickpea protein isolates showed good oil-holding capacity (3.33 g/g at pH 9) among plant proteins. Further analysis confirmed that pH had a greater influence on the structural and functional properties of proteins as compared to protein sources, particularly at acidic conditions. Overall, this study might help processors select the appropriate plant protein as dairy alternatives for their target application in plant-based food products.

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Solubility is a property of central importance for the use of proteins in research in molecular and cell biology and in applications in biotechnology and medicine. Since experimental methods for measuring protein solubility are material intensive and time consuming, computational methods have recently emerged to enable the rapid and inexpensive screening of solubility for large libraries of proteins, as it is routinely required in development pipelines. Here, we describe the development of one such method to include in the predictions the effect of the pH on solubility. We illustrate the resulting pH-dependent predictions on a variety of antibodies and other proteins to demonstrate that these predictions achieve an accuracy comparable with that of experimental methods. We make this method publicly available at https://www-cohsoftware.ch.cam.ac.uk/index.php/camsolph, as the version 3.0 of CamSol.

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Cardiolipin (CL) is a unique phospholipid featuring a dimeric structure. With its four alkyl chains, it has a large hydrophobic region and the charged hydrophilic head group is relatively small. Biological membranes exhibit CL exclusively in the inner bacterial and mitochondrial membranes. Alteration of CL packing can lead to structural changes and membrane instabilities. One environmental influence is the change in pH. Since the acidic properties of the phosphate head groups remain still controversial in literature, this work focusses on the influence of pH on the ionization degree of CL. For the analyses, surface pressure (π) - molecular area (A) isotherm experiments were combined with total reflection X-ray fluorescence (TRXF) and grazing incidence X-ray diffraction (GIXD). Continuous ionization with a high CL packing density was observed in the monolayer over a wide pH range. No individual pKa values can be assigned to the two phosphate groups, but mutual influence is observed.

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The dairy products sector is an important part of the food industry, and their consumption is expected to grow in the next 10 years. Therefore, the authentication of these products in a faster and precise way is required for the sake of public health. This review proposes the use of near-infrared techniques for the detection of food fraud in dairy products as they are faster, nondestructive, environmentally friendly, do not require sample preparation, and allow multiconstituent analysis. First, we have described frequent forms of food fraud in dairy products and the application of traditional techniques for their detection, highlighting gaps and counterproductive characteristics for the actual global food chain, as longer sample preparation time and use of reagents. Then, the application of near-infrared spectroscopy and hyperspectral imaging for the detection of food fraud mainly in cheese, butter, and yogurt are described. As these techniques depend on model development, the coverage of different dairy products by the literature will promote the identification of food fraud in a faster and reliable way.

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Under carbon source transitions, the intracellular pH of Saccharomyces cerevisiae is subject to change. Dynamics in pH modulate the activity of the glycolytic enzymes, resulting in a change in glycolytic flux and ultimately cell growth. To understand how pH affects the global behavior of glycolysis and ethanol fermentation, we measured the activity of the glycolytic and fermentative enzymes in S. cerevisiae under in vivo-like conditions at different pH. We demonstrate that glycolytic enzymes exhibit differential pH dependencies, and optima, in the pH range observed during carbon source transitions. The forward reaction of GAPDH shows the highest decrease in activity, 83%, during a simulated feast/famine regime upon glucose removal (cytosolic pH drop from 7.1 to 6.4). We complement our biochemical characterization of the glycolytic enzymes by fitting the Vmax to the progression curves of product formation or decay over time. The fitting analysis shows that the observed changes in enzyme activities require changes in Vmax , but changes in Km cannot be excluded. Our study highlights the relevance of pH as a key player in metabolic regulation and provides a large set of quantitative data that can be explored to improve our understanding of metabolism in dynamic environments.

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The increasing use of wet texturized plant proteins as meat substitutes requires a characterization of their functional properties, especially in terms of pH-behavior when being mixed with meat proteins to create so-called hybrid products. In this study, a minced model system containing pork meat, curing salt, and various amounts (0-100 wt%) of wet extruded proteins from pea (Pea I, II), pumpkin (Pumpkin I, II, III), and sunflower was used to evaluate the effect of mixing on pH and time-dependent pH-changes upon the addition of glucono-delta-lactone (GDL). Increasing concentrations of plant extrudates resulted in a linear increase of the initial (pH0h ), intermediate (pH6h ), and final pH48h for all samples and higher slopes at higher native pH of extrudates were found. Acidification kinetics of all samples were similar with a distinct pH-drop by 0.3 to 0.8 pH-units per wt% GDL in the first 6 h, followed by a plateau where pH remained constant. At extrudate concentrations of 5 wt% (Pea I, II, Pumpkin I, II) or 15 wt% (Pumpkin III, Sunflower), a sufficient acidification with typically used GDL-amounts ( = 1 wt%) could be achieved, while higher plant protein contents required higher GDL-concentrations in order to reach a pH value of 5.0; a common target value in dry-cured sausages. A mathematical model was proposed to correlate pH, time, acidifier, extrudate concentration, and plant protein origin, to aid in the adjustment of dry-cured hybrid meat formulations, and to describe thresholds of the feasible extrudate and acidifier concentrations. PRACTICAL APPLICATION: Despite the increasing relevance of texturized plant proteins as meat mimetics, little is known about their functional and process-related properties. This study shows that plant protein origin, the level of meat replacement, and the amount of acidifier are linked to the time-dependent pH-value on the basis of a mathematical model. This brings food developers one step closer in creating tailored formulations and estimating the effects of these novel ingredients in the final product characteristics of hybrid meats and analogues.

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Background: Submicron particles (SMPs), as novel bionanomaterials, offer complementary benefits to their conventional nano-counterparts. Aim: To explore zinc oxide (ZnO) SMPs' bioimaging and anticancer potentials. Materials & methods: ZnO SMPs were synthesized into two shapes. Fluorescent spectrum and microscopy were studied for the bioimaging property. Wound healing and Live/Dead assays of glioblastoma cells were characterized for anticancer activities. Results: ZnO SMPs exhibited a high quantum yield (49%) with stable orange fluorescence emission. Both morphologies (most significant in the rod shape) showed tumor-selective properties in cytotoxicity, inhibition to cell migration and attenuating the cancer-upregulated genes. The tumor selectivity was attributed to particle degradation and surface properties on pH dependency. Conclusion: The authors propose that ZnO SMPs could be a promising anticancer drug with tunable, morphology-dependent properties for bioimaging and controlled release.

Submicron particles (SMPs) are a novel nanomaterial whose total size is microscale (around one-millionth of a meter), but at least one dimension is nanoscale (around one-billionth of a meter). Their combined micro- and nanoscale properties are complementary, which can be an improvement on their conventional nano-counterparts. The aim of this study was to explore the bioimaging and anticancer properties of zinc oxide (ZnO) SMPs. ZnO SMPs were synthesized in two shapes: rod-shaped and flower-shaped. The fluorescence spectra and microscopy images were studied to investigate their potential for imaging applications, and wound healing and viability assays of glioblastoma cells were used to characterize anticancer activity. ZnO SMPs exhibited strong and stable orange fluorescence emission. Both shapes of ZnO SMPs showed tumor-selective toxicity, inhibition to cell migration and attenuating the cancer-upregulated genes; however, these effects were more significant for the rod-shaped particles. The tumor selectivity was attributed to pH-dependent particle degradation related to surface properties. The authors therefore propose that ZnO SMPs could be a promising anticancer drug with tunable, morphology-dependent properties for bioimaging and controlled release.

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The influence of the conformation of sugar beet pectin (SBP) on the interfacial and emulsifying properties was investigated. The colloidal properties of SBP, such as zeta potential and hydrodynamic diameter, were characterized at different pH levels. Furthermore, pendant drop tensiometry and quartz crystal microgravimetry were used to study adsorption behavior (adsorbed mass and adsorption rate) and stabilizing mechanism (layer thickness and interfacial tension). A more compact conformation resulted in a faster reduction of interfacial tension, higher adsorbed mass, and a thicker adsorption layer. In addition, emulsions were prepared at varying conditions (pH 3-5) and formulations (1-30 wt% MCT oil, 0.1-2 wt% SBP), and their droplet size distributions were measured. The smallest oil droplets could be stabilized at pH 3. However, significantly more pectin was required at pH 3 compared to pH 4 or 5 to sufficiently stabilize the oil droplets. Both phenomena were attributed to the more compact conformation of SBP at pH < pKa: On the one hand, pectins adsorbed faster and in greater quantity, forming a thicker interfacial layer. On the other hand, they covered less interfacial area per SBP molecule. Therefore, the SBP concentration must be chosen appropriately depending on the conformation.

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There is an increasing demand to develop and characterize high moisture extrudates from alternative plant proteins due to their increased use in various foods. In this study, wet texturized proteins from two pea isolates and four oilseed flours from pumpkin and sunflower were subjected to an acid titration to gain insights into their buffering capacity. Results were compared to pork meat with a special emphasis on compositional differences. Wet texturized pumpkin and sunflower proteins had the highest buffering capacity, especially in between pH7.0 and pH4.5, while pea protein extrudates and pork meat were more prone to acidification and similar in buffering capacity. A multiple linear regression model further revealed that ash and select minerals and amino acids are key influencing factors on the overall buffering capacity, while the effect of protein and non-protein nitrogen depends on the evaluated pH-regime. The obtained results underline the importance for a more in-depth physicochemical characterization of texturized plant proteins and their raw materials and suggest a need for recipe and process adjustment to achieve stable pH values.

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Bacillus amyloliquefaciens S0904 was selected as a hyperproducer of a glutamine-hydrolyzing enzyme which was identified as a γ-glutamyltranspeptidase catalyzing both hydrolysis and transpeptidation of glutamyl substrates. The signal peptide-truncated recombinant enzyme (rBAGGT) showed two-fold enhanced specific activity for hydrolysis and optimum pH shift to pH 7 from pH 6 compared with the wild type. The hydrolysis activity of rBAGGT was tolerant against NaCl up to 2.5 M, whereas the transpeptidation activity decreased by NaCl. At pH 6, the addition of 1.5 M NaCl not only enhanced the hydrolysis activity but also inhibited the transpeptidation activity to be ignorable. By contrast, at pH 9 in the absence of NaCl, the alkaline pH-favored transpeptidation activity was 99% of the maximum with only 15% of the maximum hydrolysis activity. In conclusion, the hydrolysis and transpeptidation activities of the recombinant BAGGT is controllable by changing pH and whether or not to add NaCl. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10068-021-00928-6.

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Red lentils (Lens culinaris) present an attractive raw material for meat mimics due to its red-coloured proteins, abundance, high protein and low cost. However, data on its functional properties at various pH remain scarce. In this study, the physicochemical and functional properties of red lentil proteins (RLP) from three origins (USA, Nepal and Turkey), isolated by isoelectric precipitation, were evaluated. Amino acid profiles, water holding (ranging from 3.1 to 3.5 g/g) and oil absorption (ranging from 5.8 to 7.3 g/g) capacities of RLP samples were significantly different (p < 0.05). RLP consisted of legumin and vicilin, and comprised predominantly glutamine/glutamic acid (ranging from 8.72 to 10.55 g/100 g). Surface charge, protein solubility, foaming and emulsifying properties were the lowest and poorest at pH 5.2 (isoelectric point). Overall, good functional properties of RLP under high acidity and alkalinity conditions make it a promising protein for mimicking a wide range of meats.

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With the increasing need for bio-based materials developed by environmentally friendly procedures, this work shows a green method to develop shape-controlled structures from cellulose dissolving pulp coated by chitosan. This material was then tested to adsorb a common and widespread pollutant, 2,4-dichlorophenol under different pH conditions (5.5 and 9). Herein it was noticed that the adsorption only occurred in acidic pH (5.5) where electrostatic interaction drove the adsorption, demonstrating the potential to tune the response under desired conditions only. The adsorption was successful in the hydrogel structure with an adsorption capacity of 905 ± 71 mg/g from a solution with 16.6 ppm; furthermore, adsorption was also possible with dried hydrogel structures, presenting a maximum of adsorption of 646 ± 50 mg/g in a similar 16.6 ppm solution. Finally, adsorbent regeneration was successfully tested for both, dry (rewetted) and never-dried states, showing improved adsorption after regeneration in the case of the never dried hydrogel structures.

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Humic acid (HA) is ubiquitous organic matter derived by microbial metabolisms. This polymeric substance has both hydrophilic and hydrophobic moieties, and it is known that they affect to bioavailability of environmental pollutants. Objective of this study is to investigate the toxicological effects of chlorophenols to green algae observed at various pH and concentration of HA. Toxicity was determined by algal growth inhibition rate and EC50 of green algae Chlorella vulgaris. As a result, toxicity of 2,4-dichlorophenol was mitigated with increase of the coexisting amount of HA and solution pH. In the case of coexisting 2.5 ppm HA, EC50 of 2,4-dichlorophenol was 12.2 ppm and approximately three times higher than the case of absence of HA at pH 7.5. Meanwhile, Toxicity of 2,4,6-trichlorophenol was enhanced with increase of the coexisting amount of HA. In the case of absence of HA, EC50 of 2,4,6-trichlorophenol was 13.1 ppm and approximately two times higher than the case of coexisting 2.5 ppm HA at pH 7.5. Results suggested that toxicity of chlorophenols is influenced by the electrostatic and hydrophobic interaction between HA and chlorophenols. The hypothesis of toxicity enhancement pathway was proposed in the case of equilibrium-state 2,4,6-trichlorophenol between anionic and nonionic states.

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Pickering emulsions are increasingly applied in the production of medicines, cosmetics, and in food technology. To apply Pickering emulsions in a rational manner it is insufficient to examine properties solely on a macroscopic scale, as this does not elucidate heterogeneities in contact angles (θ) of individual particles, which may have a profound impact on stability and microstructure. Here, we apply the super-resolution technique iPAINT to elucidate for the first time the microscopic origins of macroscopically observed emulsion phase inversions induced by a variation in particle size and aqueous phase pH. We find θ of single carboxyl polystyrene submicron particles (CPS) significantly decreases due to increasing aqueous phase pH and particle size, respectively. Our findings confirm that θ of submicron particles are both size- and pH-dependent. Interestingly, for CPS stabilized water-octanol emulsions, this enables tuning of emulsion type from water-in-oil to oil-in-water by adjustments in either particle size or pH.

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Organic anion-transporting polypeptide (OATP) 1A2 is expressed on the apical sides of intestinal and renal epithelial cells and considered to be involved in the intestinal absorption and renal reabsorption of drugs. Although the transport activity of OATP1A2 is considered to be pH-dependent, the effects of pH on its kinetic parameters and on the potency of OATP1A2 inhibitors are yet to be elucidated. Some OATP are known to have multiple binding sites (MBS), but it remains unclear whether OATP1A2 has MBS. In the present study, we evaluated the influence of pH on the OATP1A2-mediated uptake of estrone 3-sulfate using OATP1A2-expressing HEK293 cells. The uptake of 0.3 µM estrone 3-sulfate by HEK293-OATP1A2 cells was pH-dependent. OATP1A2 exhibited bimodal saturation kinetics at pH 6.3 and 7.4. Compared with that seen at pH 6.3 (5.62 µM), the Km value of the high-affinity site was 8-fold higher at pH 7.4 (43.2 µM). In addition, the influence of pH on the potency of inhibitors varied among the examined inhibitors. These results suggest that the transport properties of OATP1A2 under lower pH conditions, such as those found in the microenvironments of the small intestinal mucosa and distal tubules, differ from those seen under neutral pH conditions.

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