Sulfhydryl Research Articles

Comparison of Antioxidant and Anti-Inflammatory Effects of Honey and Spirulina platensis with Sulfasalazine and Mesalazine on Acetic Acid-Induced Ulcerative Colitis in Rats

 Background: Antioxidant therapy has gained attention for the treatment of ulcerative coli­tis (UC). The excessive generation of reactive oxygen/nitrogen species in the gastrointestinal tract increases oxidative stress, thereby leading to antioxidant defense depletion, lipid perox­idation, inflammation, tissue damage, and ulceration. Spirulina platensis (SP) and honey are excellent sources of potent antioxidants such as polyphenols and other bioactive compounds. We aimed to investigate antioxidant and anti-inflammatory effects of honey and SP in com­parison with sulfasalazine (SSZ) and mesalazine on acetic acid-induced colitis (AA-colitis) in rats. Materials and Methods: Fifty-six Sprague Dawley male rats were allocated to sev­en groups, with each group comprising eight rats. UC was induced, except in normal con­trols (NC). All groups received oral treatments for seven days. The normal saline solution of 2 mL was intrarectally administered to the NC group. The AA-colitis and NC groups received 2 mL acetic acid intrarectally as a single dose and 2 mL normal saline for seven consecutive days orally. The mesalazine group received 100 mg/kg mesalazine, the SSZ group 360 mg/kg SSZ, the honey or H group 1 mL honey diluted with 1 mL distilled water, the SH group 1g/kg SP and 1 mL honey, and the SP group 1g/kg SP. After clinical activity score assessment, the rats were sacrificed. Colonic weight/length ratio, prostaglandin E2 (PGE2), myeloperoxidase (MPO), nitric oxide (NO), malondialdehyde (MDA), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), glutathione peroxidase (GPx), total antioxidant capacity (TAC), reduced glutathione (GSH), and superoxide dismutase (SOD) were measured. Colonic histopathological changes were observed microscopically. Results: Treatment of UC with SP, honey, and combination regimen significantly reduced TNF-α, IL-1β, IL-6, MDA, MPO, NO, and PGE2, and increased TAC, GSH, GPx, and SOD in interventional groups compared to the AA-colitis group (P<0.05). Conclusion: Honey and SP might be beneficial food supple­ments for medical nutrition therapy in UC. [GMJ.2019;8:e1095]

Radiotherapy-Triggered In Situ Tumor Vaccination Boosts Checkpoint Blockaded Immune Response via Antigen-Capturing Nanoadjuvants.

In situ vaccination (ISV) formed with the aid of intratumorally injected adjuvants has shed bright light on enhancing the abscopal therapeutic effects of radiotherapy. However, the limited availability of antigens resulting from the radiotherapy-induced immunogenic cell death largely hampers the clinical outcome of ISV. To maximally utilize the radiotherapy-induced antigen, we herein developed a strategy by capturing the radiotherapy-induced antigen in situ with a nanoadjuvant comprised of CpG-loaded Fe3O4 nanoparticles. The highly efficient click reaction between the maleimide residue on the nanoadjuvant and sulfhydryl group on the antigen maximized the bioavailability of autoantigens and CpG adjuvant in vivo. Importantly, combined immune checkpoint blockade can reverse T cell exhaustion after treatment with radiotherapy-induced ISV, thereby largely suppressing the treated and distant tumor. Mechanistically, metabolomics reveals the intratumorally injected nanoadjuvants disrupt redox homeostasis in the tumor microenvironment, further inducing tumor ferroptosis after radiotherapy. Overall, the current study highlights the immense potential of the innovative antigen-capturing nanoadjuvants for synergistically enhancing the antitumor effect.

Hexagonal plate ultrasound pretreatment on the correlation between soy protein isolate structure and cholesterol-lowering activity of peptides, and protein's enzymolysis kinetics, thermodynamics

In this study, a hexagonal plate ultrasound (HPU) pretreatment technology was employed to modify soy protein isolate (SPI) and enhance the hypocholesterolemic activity of enzymatic digests from SPI. Results demonstrated that under the condition of ultrasound power density of 40 W/L, the hypocholesterolemic activity of enzymatic digests from HPU-pretreated SPI (HPU-SPI) increased by 88.40 % compared to control group after gastrointestinal digestion. The sulfhydryl content of HPU-SPI increased by a maximum of 45.32 % compared to control group. Fourier transform infrared and scanning electron microscopy revealed that HPU pretreatment partially unfolded the SPI conformation, reduced the intermolecular interactions, and exposed the internal hydrophobic regions. Pearson correlation analysis showed that sulfhydryl groups (r = 0.860), disulfide bonds (r = −0.875) and random coil (r = 0.917) were strongly correlated with the cholesterol-lowering activity of soy protein hydrolysate (SPH), following a simulated gastrointestinal digestion. Finally, the effects of HPU pretreatment on enzymolysis kinetics and thermodynamics of the SPI enzymatic process showed that HPU pretreatment significantly reduced the Mie's constant, activation energy, activation enthalpy, activation entropy and Gibbs free energy. Overall, the study outcome suggested that HPU pretreatment could positively influence the hypocholesterolemic peptide activity, and thus, may be beneficial to the pharmaceutical/food industry.

A rapid and specific fluorescent probe based on aggregation-induced emission enhancement for mercury ion detection in living systems

Mercury is a harmful heavy metal that seriously threatens the environment and organisms. In this study, we combined the aggregation-induced emission mechanism and the advantages of peptides to design a novel tetraphenylene (TPE)-based peptide fluorescent probe, TPE-Cys-Pro-Gly-His (TPE-CPGH), in which the sulfhydryl group of Cys in the peptide chain and the imidazolium nitrogen provided by His were used to mimic the Hg2+ binding site of metalloproteins. The β-fold formed by Pro-Gly was used to promote the spatial coordination of the probe with Hg2+ and the formation of the coordination complex aggregates, these changes led to the “turn on” response to Hg2+. The detection of Hg2+ by TPE-CPGH not only showed high specificity and sensitivity (LOD=46.2 nM), but also had the advantages of fast response and applicability for detection over a wide pH range. Additionally, TPE-CPGH effectively detected Hg2+ in environmental samples, living cells and organisms due to its low cytotoxicity, high water solubility and cell membrane permeability. More interestingly, TPE-CPGH was also mitigated Hg2+ exposure-induced oxidative stress toxicity in vitro and in vivo.

Manothermosonication, high-pressure homogenization, and their combinations with pH-shifting improve the techno-functionality and digestibility of hemp protein

The growing interest in plant-based proteins, particularly hemp protein, has driven the exploration of new methods to address the limitations of its industrial utilization, such as its poor functional properties. This study examined how manothermosonication (MTS) and high-pressure homogenization (HPH) techniques, along with pH-shifting, could enhance the techno-functionality of hemp protein isolate (HPI) and produce functionalized hemp protein nanoaggregates. Optimal processing conditions of MTS were 50 °C, 200 kPa, and 90 s, as determined by response surface methodology. The pH-shifting + MTS and pH-shifting + HPH treatments reduced the size of hemp protein nanoaggregates by 3.2- and 1.9-fold, respectively, compared to the untreated HPI. The changes in secondary (FTIR, CD), tertiary (SH group, fluorescence intensity), and 3D structures (XRD) confirmed modifications of treated hemp proteins. The XRD patterns showed an increase in the %crystallinity values from 21% to 29% upon the pH-shifting + MTS treatment. The combination of pH-shifting + MTS resulted in the highest solubility and digestibility, 2.1- and 1.3-fold higher than the untreated HPI, respectively, followed by the MTS-alone and HPH treatments. In addition, the emulsion properties (emulsion activity, stability, creaming index, and droplet sizes) exhibited the highest values in HPI treated by pH-shifting + MTS and + HPH. The MTS and HPH technologies provide a promising viewpoint for producing protein nanoaggregates with enhanced functional properties for microencapsulation, edible film, and other applications.

Glutathione Non-Covalent Binding Sites on Hemoglobin and Major Glutathionylation Target betaCys93 Are Conservative among Both Hypoxia-Sensitive and Hypoxia-Tolerant Mammal Species.

Intracellular tripeptide glutathione is an important agent of cell survival under hypoxia. Glutathione covalently binds to SH groups of hemoglobin cysteine residues, protecting them from irreversible oxidation, and changes its affinity to oxygen. Reduced glutathione (GSH) can also form a noncovalent complex with hemoglobin. Previously, we showed that hemoglobin tetramer has four noncovalent binding sites of glutathione GSH molecules inside, two of which are released during hemoglobin transition to deoxy form. In this study, we characterized the conserved cysteine residues and residues of noncovalent glutathione binding sites in the sequences of a number of hypoxia-tolerant and hypoxia-sensitive mammals. The solvent accessibility of all HbA and HbB residues in oxy and deoxy forms was analyzed. The alpha subunit of all species considered was shown to have no conserved cysteines, whereas the beta subunit contains Cys93 residue, which is conserved across species and whose glutathionylation changes the affinity of hemoglobin for oxygen 5-6-fold. It was found that the key residues of noncovalent glutathione binding sites in both alpha and beta subunits are absolutely conserved in all species considered, suggesting a common mechanism of hemoglobin redox regulation for both hypoxia-sensitive and hypoxia-tolerant mammals.

How Supplementation with SOD-Rich Plant Extract, Combined with Gliadin, Can Affect Oxidative Stress Markers and Zonulin Levels in Exercise-Induced Oxidative Stress.

A randomized, double-blind, placebo-controlled study was conducted to investigate the influence of supplementation with a superoxide dismutase (SOD)-rich plant extract on markers of oxidative stress, zonulin levels and the performance of elite athletes. Participants were 30 international-level rowers, divided into an experimental group (n = 15) and a control group (n = 15). The rowers performed a maximal effort incremental test on a rowing ergometer at the beginning and at the end of the study. Markers of oxidative stress (total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), superoxide dismutase (SOD), glutathione peroxidase (GPx), advanced oxidation protein products (AOPPs), malondialdehyde (MDA), sulfhydryl (SH) groups, bilirubin, uric acid, albumin and zonulin) were determined in serum. A lower TOS (p = 0.010) and OSI (p = 0.004), a lower MDA (p = 0.001) and a higher level of SH groups (p = 0.031) were observed in the experimental group after supplementation. Physical performance was evaluated through metabolic efficiency, taking lactate levels and power output on the ergometer into account. After 6 weeks of supplementation, the relative increase in metabolic efficiency at a 4 mmol/L lactate concentration and maximal effort was significantly higher in the experimental group (p = 0.004 and p = 0.015, respectively). These results suggest that supplementation with a SOD-rich extract promotes lower oxidative stress, better antioxidant protection and, consequently, the better work performance of athletes.

Sulfated iota-carrageenan from marine alga Agardhiella ramosissima prevents gastric injury in rodents via its antioxidant properties

In the present study, the gastroprotective effect of a sulfated polysaccharide isolated from marine alga Agardhiella ramosissima (SP-Ar) was investigated against alcoholic gastropathy. Gastric physiological functions and in vitro antioxidant activity also were studied. It was found that SP-Ar significantly reduced macroscopic injury and histologically maintained the architecture of gastric epithelium altered by ethanol, with maximum effect at 90 mg/kg. Importantly, animals treated with SP-Ar also had preservation of oxidative status, with reduction of nonprotein sulfhydryl groups (NP-SH) consumption and malondialdehyde (MDA) production, reduced vascular permeability, besides preventing gastric hemorrhage. In addition, SP-Ar administration did not modify gastric secretion or emptying. In vitro antioxidant data showed that SP-Ar presented high total antioxidant activity, DPPH radical scavenging, and ferrous iron chelating capacity. It was observed that SP-Ar protected gastric mucosa against alcoholic gastropathy by preventing the formation or neutralizing free radicals, associated with its intrinsic antioxidant activity. In this regard, this macromolecule should have possible application as a new therapeutic alternative or food additive to increase gastric mucosa defense.

Potential of piperine for neuroprotection in sepsis-associated encephalopathy

AimsSepsis-associated encephalopathy (SAE) is a common complication that increases mortality and leads to long-term cognitive impairment in sepsis survivors. However, no specific or effective therapy has been identified for this complication. Piperine is an alkaloid known for its anti-inflammatory, antioxidant, and neuroprotective properties, which are important characteristics for treatment of SAE. The objective of this study was to evaluate the neuroprotective effect of piperine on SAE in C57BL/6 mice that underwent cecum ligation and perforation surgery (CLP). Main methodsC57BL/6 male mice were randomly assigned to groups that underwent SHAM surgery or CLP. Mice in the CLP group were treated with piperine at doses of 20 or 40 mg/kg for short- (5 days) or long-term (10 days) periods after CLP. Key findingsOur results revealed that untreated septic animals exhibited increased concentrations of IL-6, TNF, VEGF, MMP-9, TBARS, and NLRP3, and decreased levels of BDNF, sulfhydryl groups, and catalase in the short term. Additionally, the levels of carbonylated proteins and degenerated neuronal cells were increased at both time points. Furthermore, short-term and visuospatial memories were impaired. Piperine treatment reduced MMP-9 activity in the short term and decreased the levels of carbonylated proteins and degenerated neuronal cells in the long term. It also lowered IL-6 and TBARS levels at both time points evaluated. Moreover, piperine increased short-term catalase and long-term BDNF factor levels and improved memory at both time points. SignificanceIn conclusion, our data demonstrate that piperine exerts a neuroprotective effect on SAE in animals that have undergone CLP.

Thallium(I) induces a prolonged inhibition of (6-4)photoproduct binding and UV damage excision repair activities in zebrafish (Danio rerio) embryos via protein inactivation

Cyclobutane pyrimidine dimer (CPD) and (6-4)photoproduct (6-4 PP) are two major types of UV-induced DNA lesion and 6-4 PP is more mutagenic than CPD. Activated by lesion detection, nucleotide excision repair (NER) eliminates CPDs and 6-4 PPs. Thallium (Tl) is a toxic metal existing primarily as Tl+ in the aquatic environment. Ingestion of Tl+-contaminated foods and water is a major route of human poisoning. As Tl+ may inhibit enzyme activities via binding to sulfhydryl groups, this study explored if Tl+ could intensify UV mutagenicity by inactivating NER-linked damage recognition factors using zebrafish (Danio rerio) embryo as a model system. Incubation of Tl+ (as thallium nitrate) at 0.1–0.4 μg/mL with zebrafish extracts for 20 min caused a concentration-dependent inhibition of 6-4 PP binding activities as shown by a photolesion-specific band shift assay, while CPD binding activities were insensitive to Tl+. The ability of Tl+ to suppress 6-4 PP detection was stronger than that of Hg2+. Exposure of zebrafish embryos at 1 h post fertilization (hpf) to Tl+ at 0.4–1 μg/mL for 9 or 71 h also specifically inhibited 6-4 PP detection, indicating that Tl+ induced a prolonged inhibition of 6-4 PP sensing ability primarily via its direct interaction with damage recognition molecules. Tl+-mediated inhibition of 6-4 PP binding in embryos at distinct stages resulted in a suppression of NER capacity monitored by a transcription-based DNA repair assay. Our results revealed the potential of Tl+ to enhance UV mutagenicity by disturbing the removal of 6-4 PP through repressing the lesion detection step of NER.

Effects of Baking and Frying on the Protein Oxidation of Wheat Dough.

Protein oxidation caused by food processing is harmful to human health. A large number of studies have focused on the effects of hot processing on protein oxidation of meat products. As an important protein source for human beings, the effects of hot processing on protein oxidation in flour products are also worthy of further study. This study investigated the influences on the protein oxidation of wheat dough under baking (0-30 min, 200 °C or 20 min, 80-230 °C) and frying (0-18 min, 180 °C or 10 min, 140-200 °C). With the increase in baking and frying time and temperature, we found that the color of the dough deepened, the secondary structure of the protein changed from α-helix to β-sheet and β-turn, the content of carbonyl and advanced glycation end products (AGEs) increased, and the content of free sulfhydryl (SH) and free amino groups decreased. Furthermore, baking and frying resulted in a decrease in some special amino acid components in the dough, and an increase in the content of amino acid oxidation products, dityrosine, kynurenine, and N'-formylkynurenine. Moreover, the nutritional value evaluation results showed that excessive baking and frying reduced the free radical scavenging rate and digestibility of the dough. These results suggest that frying and baking can cause protein oxidation in the dough, resulting in the accumulation of protein oxidation products and decreased nutritional value. Therefore, it is necessary to reduce excessive processing or take reasonable intervention measures to reduce the effects of thermal processing on protein oxidation of flour products.

A Novel Aptamer Biosensor Based on a Localized Surface Plasmon Resonance Sensing Chip for High-Sensitivity and Rapid Enrofloxacin Detection.

Enrofloxacin, a fluoroquinolone widely used in animal husbandry, presents environmental and human health hazards due to its stability and incomplete hydrolysis leading to residue accumulation. To address this concern, a highly sensitive aptamer biosensor utilizing a localized surface plasmon resonance (LSPR) sensing chip and microfluidic technology was developed for rapid enrofloxacin residue detection. AuNPs were prepared by the seed method and the AuNPs-Apt complexes were immobilized on the chip by the sulfhydryl groups modified on the end of the aptamer. The properties and morphologies of the sensing chip and AuNPs-Apt complexes were characterized by Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometer, and scanning electron microscope (SEM), respectively. The sensing chip was able to detect enrofloxacin in the range of 0.01-100 ng/mL with good linearity, and the relationship between the response of the sensing chip and the concentration was Δλ (nm) = 1.288log ConENR (ng/mL) + 5.245 (R2 = 0.99), with the limit of detection being 0.001 ng/mL. The anti-interference, repeatability, and selectivity of this sensing chip were studied in detail. Compared with other sensors, this novel aptamer biosensor based on AuNPs-Apt complexes is expected to achieve simple, stable, and economical application in the field of enrofloxacin detection.

Recognizing adsorption of aqueous Cr(VI), As(III), Cd(II), and Pb(II) ions by amino groups hollow polymer adsorbent

The mechanism from the molecular level and the selectivity for the removal of metal ions from aqueous has become a hotspot in current water treatment. In this study, a sulphydryl-modified hollow polymer adsorbent was designed with intrinsic amine and grafted sulphydryl groups for efficient uptake of Cr(VI), As(III), Cd(II), and Pb(II) by taking advantage of their properties of abundant functional groups, discrete hollow chambers, and high porosity. Interestingly, the benzenoid amine/quinoid imine functional groups have a stronger affinity for Cr(VI) than Cd(II) or As(III) and Pb(II). The formation of approximately 65.7% Cr(III) indicates the redox reaction from Cr(VI) to Cr(III). The electron-donating comes from benzenoid amine and oxidized to quinoid imine or protonated oxidized nitrogen units (-N = +) with Cr(VI) reduced to Cr(III) for the increase of more than double of quinoid imine and a new functional group of -N = +. Ion exchange between –COO- groups and As(III)/Cd(II), the chelation of –SH groups for Pb(II)/As(III) are plausible mechanisms.

3-Hydroxythiophenol-Formaldehyde Resin Microspheres Modulated by Sulfhydryl Groups for Highly Efficient Photocatalytic Synthesis of H2O2.

Resorcinol-formaldehyde (RF) resin represents a promising visible-light responding photocatalyst for oxygen reduction reaction (ORR) toward H2O2 production. However, its photocatalytic ORR activity toward H2O2 generation is still unsatisfied for practical application. Herein, 3-hydroxythiophenol-formaldehyde (3-HTPF) resin microspheres synthesized through polycondensation reaction between 3-HTP and formaldehyde at room temperature and subsequent hydrothermal treatment exhibit enhanced photocatalytic ORR activity is reported. The experimental results show that the partial substitution of hydroxy group (─OH) by sulfhydryl one (─SH) through using 3-HTP to replace resorcinol could slow the rates of nucleation and growth of the resin particles and lead to strongly π-stacked architecture in 3-HTPF. The introduction of ─SH group can also improve adsorption ability of 3-HTPF to O2 molecules and enhance ORR catalytic activity of the photocatalysts. Stronger built-in electric field, better adsorption ability to O2 molecules, and increased surface catalytic activity collectively boost photocatalytic activity of 3-HTPF microspheres. As a result, H2O2 production rate of 2010µmh-1 is achieved over 3-HTPF microspheres at 273K, which is 3.4 times larger than that obtained using RF submicrospheres (591µmh-1). The rational substituent group modulation provides a new strategy for designing polymeric photocatalysts at the molecular level toward high-efficiency artificial photosynthesis.

Development of sulfhydryl grafted hierarchical porous geopolymer for highly effective removal of Pb (II) from water

Geopolymers have captured increasing attention in the adsorption of lead ions due to their zeolite-like three-dimensional network structure, and several advantages such as low cost and environmental friendliness. However, their adsorption performance is limited by a small specific surface area and fewer adsorption sites. In this study, a metakaolin-based geopolymer was first pretreated with different concentrations of nitric acid to increase the porosity and surface area. Subsequently, the sulfhydryl functional group was grafted onto the above hierarchical porous geopolymer, which is a inorganic material with multistage pore structure. The result of N2 adsorption and desorption results demonstrated that an increase in specific surface area and number of grafting sites for sulfhydryl groups with increasing acid concentration when the highest nitric acid concentration used is 5 mol/L and acid treatment time is for 5 h. The specific surface area of the fabricated geopolymers was as high as 343.87 m2/g and the concentration of silanol groups reached 4.46 mmol/g at 3 mol/L acid concentration. The maximum Pb2+ adsorption quantities for SH-1HGeo, SH-2HGeo, and SH-3HGeo samples were 173.2 mg/g, 239.8 mg/g, and 386.3 mg/g, respectively. The adsorption processes were in accordance with the pseudo-second-order kinetic model and the Langmuir models, indicating that the Pb2+ adsorption on the sulfhydryl grafted hierarchical porous geopolymer was mainly chemisorption and monolayer adsorption. The contribution of different Pb2+ adsorption mechanism on geopolymer was ion-exchange, while that on SH-3HGeo was functional group complexation.

Carnosine supplementation and retinal oxidative parameters in a high-calorie diet rat model

BackgroundTo assess oxidative effects induced by a high-calorie diet on the retina of Wistar rats and test the antioxidative effects of carnosine supplementation.MethodsWistar rats were randomly divided into the following groups: standard diet (SD), high-calorie diet (HcD), standard diet + carnosine (SD + Car), and high-calorie diet + carnosine (HcD + Car). The body weight, adiposity index, plasma glucose, total lipids, high-density lipoprotein (HDL), low-density lipoprotein (LDL), uric acid, creatinine, and triglycerides of the animals were evaluated. The retinas were analyzed for markers of oxidative stress. Hydrogen peroxide production was assessed by 2',7'-dichlorodihydrofluorescein diacetate (DCF) oxidation. The total glutathione (tGSH), total antioxidant capacity (TAC), protein carbonyl, and sulfhydryl groups of the antioxidant system were analyzed.ResultsTAC levels increased in the retinas of the SD + Car group compared to the SD group (p < 0.05) and in the HcD + Car group compared to the HcD group (p < 0.05). The levels of GSH and the GSSH:GSSG ratio were increased in the HcD + Car group compared to the SD + Car group (p < 0.05). An increase in the retinal carbonyl content was observed in the HcD group compared to the SD group (p < 0.05) and in the HcD + Car group compared to the SD + Car group (p < 0.05). A high-calorie diet (HcD) was also associated with a decrease in retinal sulfhydryl-type levels compared to the SD group (p < 0.05).ConclusionThe results suggest that feeding a high-calorie diet to rats can promote an increase in carbonyl content and a reduction in sulfhydryl groups in their retinas. The administration of carnosine was not effective in attenuating these oxidative markers.Trial registrationAnimal Ethics Committee of Botucatu Medical School - Certificate number 1292/2019.

АДАПТАЦИЯ МИКРООРГАНИЗМОВ К ТЯЖЕЛЫМ МЕТАЛЛАМ

Many heavy metals (HM) (Zn, Cu, Mn, Co, etc.) take an active part in the most important processes of vital activity of microorganisms as microelements. However, at high concentrations they become toxic, and a number of metals (Pb, Hg, Cd, etc.) are highly toxic even at low concentrations. Microorganisms are able to resist the toxic effects of HMs due to the presence of various resistance mechanisms that are aimed at converting cations to a less toxic form or oxidation state, which makes them less mobile and bioavailable. The very first reaction of microorganisms to the toxic effects of metals is a change in cell morphology, their agglomeration, which leads to a decrease in the availability of binding sites for toxic metals. The mechanisms used by bacteria can be divided into biochemical and molecular. Bacterial cells have the ability to sorb metal cations with the help of metal-binding functional groups (carboxylic, sulfhydryl, hydroxyl, sulfate, phosphate, and amino groups) of the cell membrane,preventing their penetration into the cell. Bacteria have a variety of efflux systems for HM outflow from cells with the help of carrier proteins belonging to different families, which maintain a low concentration of HM inside the cell, protecting cellular components. Polysaccharides, biosurfactants, inorganic anions (phosphate, carbonate, and sulfide ions) and other metabolic products of microorganisms participate in extracellular detoxification, and gluta- thione, metal-binding proteins, intracellular polyphosphate granules, which bind HM cations into poorly soluble compounds, participate in intracellular sequestration. The reduction of HM ions with the help of enzymes leads to the formation of their less toxic forms. The genes responsible for bacterial resistance to toxic metals are localized on chromosomes or plasmids and can be transferred to closely related bacterial species, which plays an important role in the spread of HM resistance in nature. Microorganisms also demonstrate indirect mechanisms of HM tolerance aimed at maintaining cell integrity by protecting them from oxidative stress.

Improving the texture attributes of squid meat (sthenoteuthis oualaniensis) with slight oxidative and phosphate curing treatments

This study aimed to improve the pasty texture of squid meat by oxidative and phosphate curing (OPC) treatment, and elucidate the underlying mechanism. The shear force, springiness, weight gain, water-holding capacity (WHC), color and sensory evaluation of squid meat samples treated with a mild OPC approach (OPC_2, 10 mM H2O2 solution with complex phosphate solution) were significantly improved. However, the samples subjected to over-oxidized (20 and 30 mM H2O2 solution with complex phosphate solution) treatment did not obtain favorable outcomes. Microstructure analysis revealed that muscle fibers aggregated after moderate OPC treatments, leading to an increased spacing between muscle fiber bundles. This gap facilitated a more uniform distribution and restriction of water, according to low-field nuclear magnetic resonance (LF-NMR) results. The results from in vitro simulated oxidation of myofibrillar proteins (MPs) demonstrated that increased H2O2 led to formation of carbonyl groups and decreased sulfhydryl groups, and even secondary structure changes, according to fourier transform infrared spectroscopy (FT-IR). Particle size, zeta potential and sodium dodecyl sulfate-polyacryl amide gel electrophoresis (SDS-PAGE) results showed that oxidation caused protein aggregation into larger molecules. This study presents a novel approach to improve pasty texture of squid meat.

Reactive oxygen species-responsive hydrophobic crosslinked chitosan films based on triple-function crosslinkers

Chitosan is widely used in reactive oxygen species (ROS)-responsive films but remains great challenges owing to its weak mechanical strength and strong hydrophilicity. Herein, we synthesized novel hydrophobic crosslinked CS films with ROS-responsive properties and excellent physicochemical properties. A novel crosslinker, 2-((10-carboxydecyl)thio)succinic acid, with long-chain alkanes, three carboxyl groups, and sulfhydryl groups was synthesized and then used to produce thioether-containing crosslinked CS membranes. The results suggested that crosslinking could significantly increase the tensile strength of the film from 15.67 MPa to 24.32 MPa. The compact structure of crosslinked chitosan film improved the hydrophobicity and degradability, reduced the thermal stability and swelling rates, exhibited excellent non- cytotoxicity. The in vitro release studies revealed that crosslinked chitosan films could displayed the highest flux about 1.40 mg/ (cm2 h) and significant NR fluorescence change over 80 %. Collectively, our results demonstrate the applicability of these films as ROS-responsive drug delivery systems.

The effect of pH and heating on the aggregation behavior and gel properties of beef myosin

Effects of pH and heating on the structure, aggregation, and gelation of beef myosin were evaluated. The results of the changed fluorescence intensity and decreased α-helix content of all treatments demonstrated that protein structure unwound with pH and temperature. Differential scanning calorimeter (DSC) data also proved that protein head denaturation and tail denaturation occurred at 55 °C and 75 °C, respectively. The increment of hydrophobicity and the reduction of sulfhydryl group content indicated that hydrophobic interactions and disulfide bonds were beneficial to protein aggregation at 55 °C. Significantly, the content of active sulfhydryl at pH 6.0 reached its lowest value (15.61 ± 0.67 μmol/g) at 85 °C. In addition, beef myosin aggregation was corroborated by the decreased solubility and increased turbidity of all treatments. The great three-dimensional network structure could be formed at pH 6.0 above 75 °C.