Purification and thermodynamic characterization of glucose oxidase from a newly isolated strain ofAspergillus niger

An innovative multi-enzymatic system for gluconic acid production from starch using Aspergillus niger whole-cells

The use of multi-enzymatic systems for the industrial production of chemical compounds is currently considered an important green tool in synthetic organic chemistry. Gluconic acid is a multi-functional organic acid widely used in the chemical, pharmaceutical, food, textile, and construction industries. Its industrial production from glucose by fermentation using Aspergillus niger has drawbacks including high costs related to cell growth and maintenance of cell viability. This study presents an innovative one-step multi-enzymatic system for gluconic acid production from starch using Aspergillus niger whole-cells in association with amylolytic enzymes. Using soluble starch as substrate, the following results were achieved for 96 h of reaction: 134.5 ± 4.3 g/L gluconic acid concentration, 98.2 ± 1.3 % gluconic acid yield, and 44.8 ± 1.4 gGA/gwhole-cells biocatalyst yield. Although the process has been developed using starch as raw material, the approach is feasible for any substrate or residue that can be hydrolyzed to glucose.

Biochemical Insights into a Novel Family 2 Glycoside Hydrolase with Both β-1,3-Galactosidase and β-1,4-Galactosidase Activity from the Arctic

A novel GH2 (glycoside hydrolase family 2) β-galactosidase from Marinomonas sp. BSi20584 was successfully expressed in E. coli with a stable soluble form. The recombinant enzyme (rMaBGA) was purified to electrophoretic homogeneity and characterized extensively. The specific activity of purified rMaBGA was determined as 96.827 U mg-1 at 30 °C using ONPG (o-nitrophenyl-β-D-galactopyranoside) as a substrate. The optimum pH and temperature of rMaBGA was measured as 7.0 and 50 °C, respectively. The activity of rMaBGA was significantly enhanced by some divalent cations including Zn2+, Mg2+ and Ni2+, but inhibited by EDTA, suggesting that some divalent cations might play important roles in the catalytic process of rMaBGA. Although the enzyme was derived from a cold-adapted strain, it still showed considerable stability against various physical and chemical elements. Moreover, rMaBGA exhibited activity both toward Galβ-(1,3)-GlcNAc and Galβ-(1,4)-GlcNAc, which is a relatively rare occurrence in GH2 β-galactosidase. The results showed that two domains in the C-terminal region might be contributed to the β-1,3-galactosidase activity of rMaBGA. On account of its fine features, this enzyme is a promising candidate for the industrial application of β-galactosidase.

Removal of trichloroethene by glucose oxidase immobilized on magnetite nanoparticles

To overcome the safety risks and low utilization efficiency of H₂O₂ in traditional Fenton processes, in situ production of H₂O₂ by enzymatic reactions has attracted increasing attention recently. In this study, magnetite-immobilized glucose oxidase (MIG) was prepared to catalyze the heterogeneous Fenton reaction for the removal of trichloroethene from water. The successful immobilization of glucose oxidase on magnetite was achieved with a loading efficiency of 70.54%. When combined with substrate glucose, MIG could efficiently remove 5-50 mg L^-1 trichloroethene from water with a final removal efficiency of 76.2% to 94.1% by 192 h. This system remained effective in the temperature range of 15-45 °C and pH range of 3.6-9.0. The removal was slightly inhibited by different cations and anions (influencing degree Ca²⁺ > Mg²⁺ > Cu²⁺ and H₂PO₄ ^- > Cl^- > SO₄ ^2-) and humic acid. Meanwhile, the MIG could be recycled for 4 cycles and was applicable to other chlorinated hydrocarbons. The results of reactive oxidative species generation monitoring and quenching experiments indicated that H₂O₂ generated by the enzymatic reaction was almost completely decomposed by magnetite to produce ·OH with a final cumulative concentration of 129 μM, which played a predominant role in trichloroethene degradation. Trichloroethene was almost completely dechlorinated into Cl^-, CO₂ and H₂O without production of any detectable organic chlorinated intermediates. This work reveals the potential of immobilized enzymes for in situ generation of ROS and remediation of organic chlorinated contaminants.

Critical Parameters in an Enzymatic Way to Obtain the Unsweet Lactose-Free Milk Using Catalase and Glucose Oxidase Co-Encapsulated into Hydrogel with Chemical Cross-Linking

The presented work involves obtaining and characterising a two-enzymatic one-pot bioreactor, including encapsulated (co-immobilised) glucose oxidase and catalase. The enzymatic capsules were applied to produce unsweet, lactose-free milk during low-temperature catalysis. Furthermore, operational conditions, like pH and aeration, were selected in the paper, which sorts out discrepancies in literature reports. All experiments were carried out at 12 °C, corresponding to milk storage and transportation temperature. Preliminary studies (for reasons of analytical accuracy) were carried out in a buffer (pH, concentration of sugars mimicking conditions in the lactose-free milk, the initial glucose concentration 27.5 g/L) verified by processes carried out in milk in the final stage of the study. The presented results showed the need for regulating pH and the aeration of the reaction mixture in the continuous mode during the process. The procedure of co-immobilisation was performed in an alginate matrix with the cross-linking of glutaraldehyde or carbodiimide while carbodiimide showed better enzymes retention inside alginate capsules. Co-encapsulated enzymes could be used for nine cycles, preserving finally about 40% of the initial activity.

Kinetic and thermodynamic studies of novel acid phosphatase isolated and purified from Carthamus oxyacantha seedlings

Acid phosphatase (ACP) is a key enzyme in the regulation of phosphate feeding in plants. In this study, a new ACP from C. oxyacantha was isolated to homogeneity and biochemically described for the first time. Specific activity (283 nkat/mg) was found after 2573 times purification fold and (17 %) yield. Using SDS-PAGE under denaturing and nondenaturing conditions, ACP was isolated as a monomer with a molecular weight of 36 kDa. LC-MS/MS confirmed the presence of this band, suggesting that C. oxycantha ACP is a monomer. The enzyme could also hydrolyze orthophosphate monoester with an optimal pH of 5.0 and a temperature of 50 °C. Thermodynamic parameters were also determined (Ea, ΔH°, ΔG°, and ΔS°). ACP activity was further studied in the presence of cysteine, DTT, SDS, EDTA, β-ME, Triton-X-100 H₂O₂, and PMSF. The enzyme had a K_m of 0.167 mM and an Ea of 9 kcal/mol for p-nitrophenyl phosphate. The biochemical properties of the C. oxyacantha enzyme distinguish it from other plant acid phosphatases and give a basic understanding of ACP in C. oxyacantha. The results of this investigation also advance our knowledge about the biochemical significance of ACP in C. oxyacantha. Thermal stability over a wide pH and temperature range make it more suitable for use in harsh industrial environments. However, further structural and physiological studies are anticipated to completely comprehend its important aspects in oxyacantha species.

In vitro antibacterial activity of Western Australian honeys, and manuka honey, against bacteria implicated in impetigo

Impetigo is a contagious skin disease caused by Staphylococcus aureus and Streptococcus pyogenes. Without treatment, impetigo may be recurrent, develop into severe disease, or have serious, life-threatening sequelae. Standard treatment consists of topical or systemic antibiotic therapy (depending on severity), however, due to antibiotic resistance some therapies are increasingly ineffective. In this study we evaluated the potential for honey as an alternative treatment for impetigo. A broth microdilution assay in 96-well microtitre trays was used to determine the minimum inhibitory concentrations (MICs) of six monofloral honeys (jarrah, marri, red bell, banksia, wandoo, and manuka), a multifloral honey and artificial honey against S. aureus (n = 10), S. pyogenes (n = 10), and coagulase-negative staphylococci (CoNS) (n = 10). The optical density (OD) of all microtitre tray wells was also determined before and after assay incubation to analyse whether sub-MIC growth inhibition occurred. Jarrah, marri, red bell, banksia, and manuka honeys were highly effective at inhibiting S. aureus and CoNS, with MIC₅₀ values ranging from 4 to 8% w/v honey. S. pyogenes was also inhibited by these same honeys, albeit at higher concentrations (8-29% w/v). Wandoo and multifloral honeys had the least antibacterial activity with MICs of >30% (w/v) for all isolates. However, OD data indicated that sub-MIC concentrations of honey were still partially restricting bacterial growth. Our pre-clinical data indicate that honey may be a potential therapeutic agent for the routine treatment of mild impetigo, and we suggest that clinical trials would be appropriate to further investigate this.

Purification, characterization and anticancer evaluation of l-methioninase from Trichoderma harzianum

The Trichoderma harzianum l-methioninase was purified 7.15-fold with a recovery of 47.9% and the specific activity of 74.4 U/mg of protein. The purified enzyme has an apparent molecular mass of 48 kDa on SDS-PAGE and exhibited maximum activity at pH 8 and 35 °C. The enzyme was catalytically stable below 50 °C and at a pH range of 6.0-8.5. The thermal inactivation of l-methioninase exhibited first-order kinetics with the k value between 5.71 × 10-4 min-1 and 1.83 × 10-2 min-1. The studies on thermodynamic parameters of l-methioninase indicated the compaction and aggregation of the enzyme molecule during denaturation. This is the first report of thermodynamic analysis of thermal inactivation in l-methioninase. The enzyme activity was enhanced by Li+ and inhibited by Cu2+, Co2+, Fe2+, Hydroxylamine and PMSF. The purified enzyme showed K m , V max and k cat value of 1.19 mM, 21.27 U/mg/min and 16.11 s-1, respectively. The l-methioninase inhibited the growth of human cell lines hepatocellular carcinoma (Hep-G2) and breast carcinoma (MCF-7) with IC50 values of 14.12 μg/ml and 20.07 μg/ml, respectively. The in vivo antitumor activity of l-methioninase was evaluated against DAL cell lines bearing in Swiss albino mice. The enzyme effectively reduced tumor volume, packed cell volume, viable cell count and restored hematological parameters, serum enzyme and lipid profile to normal levels compared to DAL control mice. The present study has demonstrated the high efficacy of Trichoderma harzianum l-methioninase against cancer cell lines in vitro and in vivo conditions. The purified l-methioninase has significant thermal stability and better catalytic properties than the enzyme purified from other sources.

Exploiting the activity-stability trade-off of glucose oxidase from Aspergillus niger using a simple approach to calculate thermostability of mutants

Glucose oxidase (Gox) is a biocatalyst that is widely applied in the food industry, as well as other biotechnological industries. However, the industrial application of Gox is hampered by its low thermostability and activity. Here, we aimed to improve the thermostability of GoxM4 from Aspergillus niger without reducing its activity due to the activity-stability trade-off. A simple and effective approach combining enzyme activity and structure stability was adopted to evaluate the thermostability of GoxM4 and its mutants. After four rounds of computer-aided rational design, the best mutant, GoxM8, was obtained. The melting temperature (T_m) of GoxM8 was increased by 9 °C compared with GoxM4. The catalytic efficiency of GoxM8 was similar to GoxM4, suggesting that the enzyme activity-stability trade-off was counteracted. To explore its mechanism, we performed molecular dynamics simulations of GoxM4 and its mutants. Our findings provided a typical example for researching the enzyme activity-stability trade-off.

Artificial Bifunctional Photozyme of Glucose Oxidase-Peroxidase for Solar-Powered Glucose-Peroxide Detection in a Biofluid with Resorcinol-Formaldehyde Polymers

Photozymes or artificial photosynthesis based on alternative natural enzymes is vital for the sustainable development of next-generation healthcare, energy, and materials science. Herein, we report resorcinol-formaldehyde (RF) resins as a solar-driven metal-free bifunctional glucose oxidase-peroxidase stand-alone photozyme for the colorimetric dual detection of hydrogen peroxide and glucose. The π-bond conjugated benzenoid-ortho/para quinoid RF polymers are efficient for glucose oxidation and hydrogen peroxide reduction with concurrent 3,3',5,5'-tetramethylbenzidine oxidation under natural sunlight. The photoinduced colorimetric process could detect H₂O₂ up to 3.5 μM at 652 nm with the linear range of 0.1-2 mM. A limit of detection of 9.2 μM was exhibited by the system while measuring glucose with a linearity from 0.2 to 8.5 mM. The formation of hydroxyl radicals (^•OH) from glucose oxidation reactions was evidenced by spin trapping electron paramagnetic resonance studies conducted herein. The results indicated that RF resins possessed strong intrinsic glucose oxidase and peroxidase (POx)-like activity under natural sunlight with promising storage and operation. This simple photozyme will definitely have potential uses in biomimetic solar-driven catalysis, bioenergy, and biomedicine.

Investigating the Impact of Various Parameters On the Activity of Acid Phosphatases from Seedlings of Coronopus didymus

The thermal stability of purified acid phosphatase from the germinating seedlings of Coronopus didymus (Jangli halon) was investigated by studying the impact of various thermodynamic parameters [t_1/2, E_d, ΔH° (enthalpy change), ΔG° (free energy change), and ΔS° (entropy change)] of heat treatment in the temperature range of 55-75 °C. The thermal denaturation of acid phosphatase, assessed by loss in activity, was evidently followed by first-order kinetics, which varies with time and yield during the process of denaturation. The half-life of the enzyme was 693 min at 55 °C. The E_d (activation energy of denaturation) was calculated by the Arrhenius plot (30 kcal mol^-1), and the Z-value was 17.3 °C. The various thermodynamic parameters studied were as follows: ΔH°, the change in enthalpy of inactivation, was 121.93 kJ mol^-1 at 55 °C; ΔG°, the change in free energy of inactivation, was 110.65 kJ mol^-1 at 55 °C; and ΔS°, the change in entropy of inactivation, was 34.39 J mol^-1 k^-1 at 55 °C. This suggests that acid phosphatase activity is thermostable to long heat treatment up to 60 °C.

Proteomic Identification of Protein Glutathionylation in Cardiomyocytes

Reactive oxygen species (ROS) are important signaling molecules, but their overproduction is associated with many cardiovascular diseases, including cardiomyopathy. ROS induce various oxidative modifications, among which glutathionylation is one of the significant protein oxidations that occur under oxidative stress. Despite previous efforts, direct and site-specific identification of glutathionylated proteins in cardiomyocytes has been limited. In this report, we used a clickable glutathione approach in a HL-1 mouse cardiomyocyte cell line under exposure to hydrogen peroxide, finding 1763 glutathionylated peptides with specific Cys modification sites, which include many muscle-specific proteins. Bioinformatic and cluster analyses found 125 glutathionylated proteins, whose mutations or dysfunctions are associated with cardiomyopathy, many of which include sarcomeric structural and contractile proteins, chaperone, and other signaling or regulatory proteins. We further provide functional implication of glutathionylation for several identified proteins, including CSRP3/MLP and complex I, II, and III, by analyzing glutathionylated sites in their structures. Our report establishes a chemoselective method for direct identification of glutathionylated proteins and provides potential target proteins whose glutathionylation may contribute to muscle diseases.

Biochemical and Thermodynamical Characterization of Glucose Oxidase, Invertase, and Alkaline Phosphatase Secreted by Antarctic Yeasts

The use of enzymes in diverse industries has increased substantially over past decades, creating a well-established and growing global market. Currently, the use of enzymes that work better at ambient or lower temperatures in order to decrease the temperatures of production processes is desirable. There is thus a continuous search for enzymes in cold environments, especially from microbial sources, with amylases, proteases, lipases and, cellulases being the most studied. Other enzymes, such as glucose oxidase (GOD), invertase (Inv), and alkaline phosphatase (ALP), also have a high potential for application, but have been much less studied in microorganisms living in cold-environments. In this work, secretion of these three enzymes by Antarctic yeast species was analyzed, and five, three, and five species were found to produce extracellular GOD, Inv, and ALP, respectively. The major producers of GOD, Inv, and ALP were Goffeauzyma gastrica, Wickerhamomyces anomalus, and Dioszegia sp., respectively, from which the enzymes were purified and characterized. Contrary to what was expected, the highest GOD and Inv activities were found at 64°C and 60°C, respectively, and at 47°C for ALP. However, the three enzymes maintained a significant percentage of activity at lower temperatures, especially ALP that kept a 67 and 43% of activity at 10°C and 4°C, respectively.

Synthesis of glucose oxidase-PEG aldehyde conjugates and improvement of enzymatic stability

In this article, aldehyde derivative of poly(ethylene glycol) (PEG) was synthesized directly with sodium periodate agent. To obtain a conjugate which possesses better stability, PEG aldehyde was bonded to native enzyme with different molar ratios. The conjugation reaction turned out to be efficient and mild. Colorimetric method was applied to evaluate the enzymatic activity of native GOD and its derivatives by introducing another enzyme, horseradish peroxidase. The GOD-PEG aldehyde conjugate with polymeric chains exhibited reduced enzymatic activity towards the catalytical oxidation of glucose, but with significantly increased thermal stability and elongated lifetime. When GOD was modified with PEG aldehyde the enzymatic activity was decreased 40% at 30 °C. However, when incubated at 60 °C the GOD-PEG aldehyde conjugate still retained the enzyme bioactivity of 40% bioactivity left after 4 h, whereas the native GOD lost almost all the activity in 4 h. The polymer chain attached, the more reduction of the enzymatic activity resulted, however, the longer the lifetime and higher thermal stability of the enzyme obtained.

Molecular cloning and sequence analysis of a PVGOX gene encoding glucose oxidase in Penicillium viticola F1 strain and it's expression quantitation

The PVGOX gene (accession number: KT452630) was isolated from genomic DNA of the marine fungi Penicillium viticola F1 by Genome Walking and their expression analysis was done by Fluorescent RT-PCR. An open reading frame of 1806bp encoding a 601 amino acid protein (isoelectric point: 5.01) with a calculated molecular weight of 65,535.4 was characterized. The deduced protein showed 75%, 71%, 69% and 64% identity to those deduced from the glucose oxidase (GOX) genes from different fungal strains including; Talaromyces variabilis, Beauveria bassiana, Aspergillus terreus, and Aspergillus niger, respectively. The promoter of the gene (intronless) had two TATA boxes around the base pair number -88 and -94 and as well as a CAAT box at -100. However, the terminator of the PVGOX gene does not contain any polyadenylation site (AATAAA). The protein deduced from the PVGOX gene had a signal peptide containing 17 amino acids, three cysteine residues and six potential N-linked glycosylation sites, among them, -N-K-T-Y- at 41 amino acid, -N-R-S-L- at 113 amino acid, -N-G-T-I- at 192 amino acid, -N-T-T-A at 215 amino acid, -N-F-T-E at 373 amino acid and -N-V-T-A- at 408 amino acid were the most possible N-glycosylation sites. Furthermore, the relative transcription level of the PVGOX gene was also stimulated in the presence of 4% (w/v) of calcium carbonate and 0.5 % (v/v) of CSL in the production medium compared with that of the PVGOX gene when the fungal strain F1 was grown in the absence of calcium carbonate and CSL in the production medium, suggesting that under the optimal conditions, the expression of the PVGOX gene responsible for gluconic acid biosynthesis was enhanced, leading to increased gluconic acid production. Therefore, the highly glycosylated oxidase enzyme produced by P. viticola F1 strain might be a good producer in the fermentation process for the industrial level production of gluconic acid.

Enhanced thermal stability and pH behavior of glucose oxidase on electrostatic interaction with polyethylenimine

Electrostatic interactions, mediated by ionic-exchange, between polyethylenimine (PEI) and glucose oxidase (GOx) were used to form GOx-PEI macro-complex, which were evaluated for pH and thermal stability of GOx. Under the experimental conditions, the complex had a dominant GOx presence on its surface and a hydrodynamic diameter of 205 ± 16 nm. Activity was evaluated from 40 to 75 °C, and at pH from 2 to 12. GOx activity in complex was maintained up to 70 °C and it was lost at 75 °C. In contrast, free GOx showed a maximum activity at 50 °C, which was completely lost at 70 °C. This difference, observed by fluorescence analysis, was associated with the compact unfolded structure of GOx in the complex. This GOx stability was not observed under pH variations, and complex formation was only possible at pH ≥ 5 where enzymatic activity was diminished by the presence of PEI.

Isolation and biochemical characterization of a glucose dehydrogenase from a hay infusion metagenome

Glucose hydrolyzing enzymes are essential to determine blood glucose level. A high-throughput screening approach was established to identify NAD(P)-dependent glucose dehydrogenases for the application in test stripes and the respective blood glucose meters. In the current report a glucose hydrolyzing enzyme, derived from a metagenomic library by expressing recombinant DNA fragments isolated from hay infusion, was characterized. The recombinant clone showing activity on glucose as substrate exhibited an open reading frame of 987 bp encoding for a peptide of 328 amino acids. The isolated enzyme showed typical sequence motifs of short-chain-dehydrogenases using NAD(P) as a co-factor and had a sequence similarity between 33 and 35% to characterized glucose dehydrogenases from different Bacillus species. The identified glucose dehydrogenase gene was expressed in E. coli, purified and subsequently characterized. The enzyme, belonging to the superfamily of short-chain dehydrogenases, shows a broad substrate range with a high affinity to glucose, xylose and glucose-6-phosphate. Due to its ability to be strongly associated with its cofactor NAD(P), the enzyme is able to directly transfer electrons from glucose oxidation to external electron acceptors by regenerating the cofactor while being still associated to the protein.