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Oxalic acid and oxalates are secondary metabolites secreted to the surrounding environment by fungi, bacteria, and plants. Oxalates are linked to a variety of processes in soil, e.g. nutrient availability, weathering of minerals, or precipitation of metal oxalates. Oxalates are also mentioned among low-molecular weight compounds involved indirectly in the degradation of the lignocellulose complex by fungi, which are considered to be the most effective degraders of wood. The active regulation of the oxalic acid concentration is linked with enzymatic activities; hence, the biochemistry of microbial biosynthesis and degradation of oxalic acid has also been presented. The potential of microorganisms for oxalotrophy and the ability of microbial enzymes to degrade oxalates are important factors that can be used in the prevention of kidney stone, as a diagnostic tool for determination of oxalic acid content, as an antifungal factor against plant pathogenic fungi, or even in efforts to improve the quality of edible plants. The potential role of fungi and their interaction with bacteria in the oxalate-carbonate pathway are regarded as an effective way for the transfer of atmospheric carbon dioxide into calcium carbonate as a carbon reservoir. [ABSTRACT FROM AUTHOR]

A biosensor is considered an integrated receptor transducer device, with the ability to convert a biological impulse into an electrical signal. The amendment of biosensors has been recognized for its great potential by many researchers, due to its numerous applications e.g., environmental management, disease diagnosis, agricultural aspects, food companies, health care, drug monitoring, and water treatment as it can be used in the detection of water quality. Moreover, technological development of the biosensor is integrated with several merits such as affordability and enhancement in medical fields in disease detection and body response; furthermore, it is easy to use, effective, and scalable. This article briefly reviews how to construct an oxalic acid (OA) biosensor by integration of tissue enzymes and peroxide simulated enzymes. OA is converted to peroxide (H2O2) and carbon dioxide (CO2) with the help of the oxalate oxidase (OxOx) present in spinach leaves as catalyst. Afterwards, with the presence of cobalt ferrite (CoFe2O4), nanoparticles (NPs) have a catalytic effect on concentrated H2O2 and chemiluminescence (CL) luminol (C8H7N3O2). Therefore, CL flow can be constructed under a biosensor to determine OA in the sample. The co-presence of tissue column and CoFe2O4, as well as a high level of relative CL intensity can be obtained. The biosensor based on H2O2 and involving inorganic nanomaterials has many advantages such as high efficiency, affordability, outstanding sensitivity, stability and selectivity, a fast response, and an extended range of linearity with a lower detection limit. In addition, optimization factors for the oxalate biosensor, limitations, and outlooks for the biosensor were also highlighted. [ABSTRACT FROM AUTHOR]

We describe an enzymatic fuel cell (EFC) that can electrooxidize glucose completely. The EFC contains the hybrid Ni@Pt-CNT/OxOx bioanode, composed of a bimetallic composite catalyst (Ni@Pt-CNT) and the enzyme oxalate oxidase (OxOx), which can cleave carbon-carbon bonds. Ni@Pt-CNT/OxOx displayed 3-fold higher catalytic activity in the presence than in the absence of glucose (1.3 and 0.4 mA cm−2, respectively), indicating that Ni@Pt-CNT and OxOx acted synergistically. Electrochemical impedance spectroscopy showed that Ni@Pt-CNT/OxOx had higher charge transfer resistance and double layer capacitance than Ni@Pt-CNT. Long-term bulk electrolysis (18 h) revealed that the EFC operating with Ni@Pt-CNT/OxOx presented better current density and stability than the electrochemical cell operating with Ni@Pt-CNT, so deep glucose electrooxidation generated energy. The glucose oxidation products detected by HPLC-UV/RID confirmed that glucose was fully electrooxidized, and that 24 electrons were harvested from it. The hybrid Ni@Pt-CNT/OxOx bioanode developed herein could be used in cascade reactions, to provide an EFC with promising application in self-powered electronic devices.

Oxalate oxidase (EC 1.2.3.4) is an oxalate-decomposing enzyme predominantly found in plants but also described in basidiomycete fungi. In this study, we investigated 23 fungi to determine their capability of oxalic acid degradation. After analyzing their secretomes for the products of the oxalic acid-degrading enzyme activity, three groups were distinguished among the fungi studied. The first group comprised nine fungi classified as oxalate oxidase producers, as their secretome pattern revealed an increase in the hydrogen peroxide concentration, no formic acid, and a reduction in the oxalic acid content. The second group of fungi comprised eight fungi described as oxalate decarboxylase producers characterized by an increase in the formic acid level associated with a decrease in the oxalate content in their secretomes. In the secretomes of the third group of six fungi, no increase in formic acid or hydrogen peroxide contents was observed but a decline in the oxalate level was found. The intracellular activity of OXO in the mycelia of Schizophyllum commune, Trametes hirsuta, Gloeophyllum trabeum, Abortiporus biennis, Cerrena unicolor, Ceriosporopsis mediosetigera, Trametes sanguinea, Ceriporiopsis subvermispora, and Laetiporus sulphureus was confirmed by a spectrophotometric assay. [ABSTRACT FROM AUTHOR]

Abstract The present research evaluated the anti urolithic potential of Cyperus rotundus tubers extract using in silico, in vitro and in vivo techniques. In silicostudy was performed of Cyperus rotundus constituents and pathological protein oxalate oxidase (PDB Id: 2ETE). In vitrostudy, nucleation and aggregation assay involved for assessment of ethanol extract of Cyperus rotundus tuber (50-3000 µg/ml).In vivo studies involved that the Cyperus rotundusethanolic extract (100, 200 and 400 mg/kg B.wt.) wastreatedonsodium oxalate induced urolithiatic rats for seven days,evaluated kidney function by urine and serum biochemical analysis and statistical analysis performed usingGraphPad prism5 software.In silico results showedthat Cyperus rotundus constituents,Humulene epoxide, 4-Oxo-alpha-ylangene, Cubebol were exhibited better binding energyonoxalate oxidase.Ethanolic extract of Cyperus rotundustuber was exhibited nucleation, aggregation of calcium oxalate monohydrate crystals inhibition in dosedependent manner. Sodium oxalate treatment was triggered biochemical changesin the urine that have been substantially prevented by the ethanolic extract of Cyperus rotundus tuber. The current findings Cyperus rotundus anti urolithic activity due to antioxidant essential oils. The molecular docking results could be used to optimize lead and develop the appropriate urolithiasis treatment.

This study describes the development of an ethylene glycol (EG) biofuel cell that combines the organic catalyst 4‐amino‐TEMPO (TEMPO‐NH2) and the enzyme oxalate oxidase (OxOx) in solution for complete EG oxidation. Cyclic voltammetric curves recorded in the presence of EG showed that the hybrid TEMPO‐NH2/OxOx catalyst provided 1.2 higher current density than the TEMPO‐NH2 catalyst. Chronoamperometric assays after successive EG injections and long‐term electrolysis at a fixed potential of 0.75 V (vs Ag/AgCl) showed that the hybrid TEMPO‐NH2/OxOx catalyst in the presence of EG promoted 14 % and 58 % increase in the current obtained with the TEMPO‐NH2 catalyst, respectively. High‐performance liquid chromatography (HPLC) results confirmed that TEMPO‐NH2 and OxOx respectively acted on EG oxidation and C−C bond cleavage, leading to complete EG oxidation, harvesting all 10 of the EG electrons and high catalytic activity. [ABSTRACT FROM AUTHOR]

Oxalic acid (OA) is a crucial pathogenic factor for Sclerotinia spp. fungi, which is closely related to Botrytis spp. fungi. Whether OA is a pathogenic factor for the causal agent of grey mould in lily, Botrytis elliptica, and the response of lily to OA are poorly understood.To address these questions, lesion tissues and deposition of calcium oxalate (CaOX) and callose were observed in diploid and tetraploid leaves of L. rosthornii after inoculation with B. elliptica. Oxalate oxidase (OXO) activity and the transcript levels of some genes related to OA degradation (LrGLP1, LrGLP2 and LrWRKY4), reactive oxygen species (ROS) production/scavenging systems (LrRBOHD, LrGST, LrPOD and LrAPX1) and pathogen‐related protein (PR) synthesis (LrCHI, LrBGL and LrPR10) were compared.After diploid and tetraploid leaves inoculation, lesion tissue and callose and CaOX were separately observed around in guard cells and stomata rather than the epidermis in the infected area. OXO activity was triggered at 2 h post‐inoculation (hpi) in both ploidy leaves, and it was higher in the latter from 12‐48 hpi. Expression of LrGLP1, LrGLP2, LrRBOHD, LrGST, LrPOD, LrCHI, LrBGL and LrPR10 was higher in tetraploids than in diploids from 24(12)–36(48) hpi.In conclusion, for B. elliptica, OA mainly chelates Ca2+ from the stomata cell wall. The strong capability to degrade OA and higher expression levels of some genes related to ROS accumulation/scavenging and PR synthesis may partially explain the relatively higher grey mould resistance of tetraploid L. rosthornii. [ABSTRACT FROM AUTHOR]

Oxalate oxidase (OxO), a manganese dependent enzyme, is involved in the catalysis of oxalate oxidation to carbon dioxide with the formation of hydrogen peroxide. OxO is present in the cell wall of plants. It increases the resistivity against diseases and external stress. Oxalate is found as waste metabolites in mammals, excess accumulation of oxalate results in hyperoxaluria and urolithiasis in humans. These disorders can be diagnosed by the help of OxO in many analytical methods. The present study is aimed on isolation of OxO enzyme from Pseudomonas strain under high salt stress. The OxO enzyme was produced in bulk under selected salt stress. It was partially purified by ammonium sulphate precipitation method, dialysis and ion-exchange chromatography. The OxO enzyme on enzymatic analysis showed potent activity concerning oxalic acid substrate. The microtiter plate analysis confirmed the ability of OxO enzyme purified from Pseudomonas strain in the diagnosis of oxalate-related disorders and in the future could be used to prepare the diagnostic biosensors. [ABSTRACT FROM AUTHOR]

This research aimed to study granular and molecular structures, physicochemical, and functional properties of the starch extracted from a novel, dasheen type of taro conserved, and cultivated by several generations of Kunabi tribes of Joida, Karnataka, India. Further, an enzymatic (oxalate oxidase) and chemical (phosphoric acid) treatment processes are evaluated for reducing total oxalate content in the starch extracted from the taro flour. The total oxalate content of the taro flour is found to be 2344 mg 100 g−1, and the starch yield is about 45% in all the methods. The oxalate oxidase (OxO) and phosphoric acid treatment reduced the total oxalate content by 98.37% and 98.03%, respectively. The residual oxalate content in the resultant starch is within the threshold limit (71 mg 100 g−1). The study of characteristic properties of enzyme‐treated (ET), phosphoric acid‐treated (PT), and native starch (NT) revealed minor changes in ET and PT compared to NT. [ABSTRACT FROM AUTHOR]

Taro (Colocasia esculenta) starch is known to possess unique physical and functional properties such as low amylose content, A-crystalline form, small granules, higher swelling power, etc. Due to the presence of significant amount of calcium oxalate crystals, the food industry is reluctant to explore this unique and cheap starch source for various food applications. Traditional processes utilizing various physical and chemical methods to remove oxalate content of starch inevitably change its physical and functional properties. However, using oxalate oxidase can effectively remove oxalates without altering the unique properties of starch. Hence, an attempt was made to optimize oxalate oxidase assisted starch extraction process from taro flour using response surface methodology. A central composite design comprising 20 experimental trials with 10 cube points augmented with six axial points and four replicates at the center point was applied. A mathematical model was developed to show the effect of taro flour concentration, enzyme load and incubation time on the oxalate removal. Validity of the model was experimentally verified and found that 98.3% of total oxalates can be removed under optimal conditions. This is the first report of optimization of the production of starch from taro flour using microbial oxalate oxidase. [ABSTRACT FROM AUTHOR]

Four oxalate degrading endophytic bacteria were isolated from oxalate rich Colocasia esculenta tubers. Based upon the oxalate oxidase (EC 1.2.3.4) activity produced in nutrient medium, one bacterium was selected and identified as Ochrobactrum intermedium by 16S rDNA sequencing. Studies on effect of nutritional and non-nutritional parameters showed that oxalate oxidase production is inducible, requires Manganese ions in the medium, and very low fill-up volume is beneficial. Shake flask fermentation carried out with medium comprising Sucrose, Ammonium chloride, Sodium oxalate along with basal salts gave 0.5 UmL-1 oxalate oxidase activity and 0.454 Umg-1specific activity after 65h of fermentation.

Calcium oxalate (nephrolithiasis) is the most frequent type of kidney stone disease (KSD) affecting the urinary tract. In this study, the degradation and excretion of oxalate from body was carried out by utilizing oxalate oxidase producing bacterial strains. Bacterial strains were isolated from medical waste dumped soil and analyzed for its oxalate oxidase activity by using calcium oxalate, L-ascorbic acid, and oxalic acid and their ability to degrade the substrates was studied. Also, the optimized condition for the effective enzyme activity was found to be higher at pH - 5, temperature (40°C), substrates (Calcium oxalate & Oxalic acid), ZnO metal (0.01 mg/mL) and chelating agent (EDTA) of 0.01 mg/mL concentration. Further, ammonium sulphate precipitation of 50% saturation was performed and then partially purified by dialysis. The optimization for the partially purified enzyme activity was executed and the optimized conditions are temperature (400C), substrates (Oxalic acid), and pH (5). In vitro analysis of the kidney stone formation was tested for the partially purified enzyme and identified to be the potential source for the treatment of kidney stones. [ABSTRACT FROM AUTHOR]

We have described for the first time the localisation of oxalate oxidase (OXO, EC 1.2.3.4) in Abortiporus biennis cells, using histochemical and immunochemical methods coupled with transmission electron microscopy. Rabbit anti-oxalate oxidase immunoglobulins with anti-rabbit secondary antibody conjugated with 10-nm gold particles were used. Moreover, the formation of electron dense precipitation of reaction of diaminobenzidine (DAB) with horseradish peroxidase (HRP) for histochemical localisation of the enzyme was found. OXO was localised close to the membranous structures of the cell membranes, in membranous vesicles located close to the outer cell membrane, and vacuolar membranes surrounding vacuoles. The positive immunoreaction to OXO was also intense in cell wall areas. Moreover, we proved that gene coding for OXO was expressed in the same cultures. Corresponding mRNA was isolated, full length cDNA was synthesized, cloned and sequenced. Two copies of cupin domains were found in the sequence of amino-acids conserved domain coding for the cupin enzyme. Comparison of the genomic DNA and cDNA sequences has revealed the presence of seventeen introns in the gene. The isoelectric point of the protein was estimated at pH 4.5 and several possible N-glycosylation sites were predicted. [ABSTRACT FROM AUTHOR]

Oxalate oxidase enzyme in monocotyledonous plants, act as a scavenger to breakdown oxalic acid into carbon dioxide and hydrogen peroxide. They perform several important functions in early plant defence responses, including induction of PR protein synthesis and systemic resistance. In the present study oxalic acid, the virulence factor of fungi, was applied to monocotyledonous plants and it was observed that it activates the innate host immune system, along with secretion of oxalate oxidase. The enzymatic activities of other host defence related enzymes like catalase, superoxide dismutase, ascorbic acid oxidase, phenolic content, phenylalanine ammonia lyase were compared between the control and oxalic acid treated (2mM) plants. [ABSTRACT FROM AUTHOR]

Abstract The germin-like protein (GLP) purified from Thevetia peruviana , Peruvianin-I, is the only one described as having proteolytic activity. Therefore, the goal of this study was to investigate the structural features responsible for its enzymatic activity. Although the amino acid sequence of Peruvianin-I showed high identity with other GLPs, it exhibited punctual mutations, which were responsible for the absence of oxalate oxidase activity. The phylogenetic analysis showed that Peruvianin-I does not belong to any classification of GLP subfamilies. Moreover, Peruvianin-I contains a catalytic triad found in all plant cysteine peptidases. Molecular docking simulations confirmed the role of the catalytic triad in its proteolytic activity. Synchrotron radiation circular dichroism assays confirmed that Peruvianin-I was stable at pH ranging from 5.0 to 8.0 and that it presented significant structural changes only above 60 °C. The addition of iodoacetamide caused changes in its native conformation, but only a slight effect was observed after adding a reducing agent. This study reports an unusual protein with germin-like structure, lacking typical oxalate oxidase activity. Instead, the proteolytic activity observed suggests that the protein is a cysteine peptidase. These structural peculiarities make Peruvianin‑I an interesting model for further understanding of the action of laticifer fluids in plant defense. [ABSTRACT FROM AUTHOR]

Abstract Oxalic acid is a naturally occurring metabolite in plants and a common constituent of all plant-derived human diets. Oxalic acid has diverse unrelated roles in plant metabolism, including pH regulation in association with nitrogen metabolism, metal ion homeostasis and calcium storage. In plants, oxalic acid is also a pathogenesis factor and is secreted by various fungi during host infection. Unlike those of plants, fungi and bacteria, the human genome does not contain any oxalate-degrading genes, and therefore, the consumption of large amounts of plant-derived oxalate is considered detrimental to human health. In this review, we discuss recent biotechnological approaches that have been used to reduce the oxalate content of plant tissues. Graphical abstract Image Highlights • Oxalic acid is an antinutrient in humans and a pathogenesis factor in plants. • Consumption of high oxalate diet may lead to hyperoxaluria and harm renal tissues. • Genetically engineered crops for low oxalate content have been developed. • Understanding of oxalate metabolism could provide insights for crop improvement. [ABSTRACT FROM AUTHOR]

Kochia sieversiana (Pall.) C.A. Mey. is a forage plant that can grow in extremely alkalinized grasslands at pH 10 or higher. Accumulation of a large amount of oxalic acid (OxA) is a primary characteristic of K. sieversiana. In our study, seedlings of K. sieversiana were exposed to the following conditions: non-stress, salinity (200 mM, a molar ratio of NaCl and Na2SO4 1:1), and alkali stress (200 mM, a molar ratio of NaHCO3 and Na2CO3 1:1). Growth, water content, content of organic acids (including OxA), Na+, and K+, and activities of some OxA metabolism-related enzymes were determined. Results show that glycolate oxidase was the key enzyme for OxA synthesis; however, the carboxylation of phosphoenolpyruvate (PEP) by PEP carboxylase (PEPC) probably played a minor role in the OxA-synthetic pathway. The pathway of L-ascorbic acid catabolism was not the main source of OxA accumulation, and the activity of oxalate oxidase (OxO) involved in OxA decomposition was not a limiting factor for inner OxA accumulation. Taken together, accumulation of a large amount of OxA are not related to the degradation and secretion function of OxO but largely depend upon its synthetic function.

Isothermal titration calorimetry (ITC) may be used to determine the kinetic parameters of enzyme-catalyzed reactions when neither products nor reactants are spectrophotometrically visible and when the reaction products are unknown. We report here the use of the multiple injection method of ITC to characterize the catalytic properties of oxalate oxidase (OxOx) from Ceriporiopsis subvermispora (CsOxOx), a manganese dependent enzyme that catalyzes the oxygen-dependent oxidation of oxalate to carbon dioxide in a reaction coupled with the formation of hydrogen peroxide. CsOxOx is the first bicupin enzyme identified that catalyzes this reaction. The multiple injection ITC method of measuring OxOx activity involves continuous, real-time detection of the amount of heat generated (dQ) during catalysis, which is equal to the number of moles of product produced times the enthalpy of the reaction (ΔHapp). Steady-state kinetic constants using oxalate as the substrate determined by multiple injection ITC are comparable to those obtained by a continuous spectrophotometric assay in which H2O2 production is coupled to the horseradish peroxidase-catalyzed oxidation of 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) and by membrane inlet mass spectrometry. Additionally, we used multiple injection ITC to identify mesoxalate as a substrate for the CsOxOx-catalyzed reaction, with a kinetic parameters comparable to that of oxalate, and to identify a number of small molecule carboxylic acid compounds that also serve as substrates for the enzyme.

Calcium oxalate (CaOx) crystals are widespread among plant species. Their functions are not yet completely understood; however, they can provide tolerance against multiple environmental stress factors. Recent evidence suggested that CaOx crystals function as carbon reservoirs since its decomposition provides CO2 that may be used as carbon source for photosynthesis. This might be advantageous in plants with reduced mesophyll conductance, such as the Antarctic plant Colobanthus quitensis, which have shown CO2 diffusion limitations. In this study, we evaluate the effect of two CO2 concentrations in the CaOx crystals decomposition and chlorophyll fluorescence of C. quitensis. Plants were exposed to airflows with 400 ppm and 11.5 ppm CO2 and the number and relative size of crystals, electron transport rate (ETR), and oxalate oxidase (OxO) activity were monitored along time (10 h). Here we showed that leaf crystal area decreases over time in plants with 11.5 ppm CO2, which was accompanied by increased OxO activity and only a slight decrease in the ETR. These results suggested a relation between CO2 limiting conditions and the CaOx crystals decomposition in C. quitensis. Hence, crystal decomposition could be a complementary endogenous mechanism for CO2 supply in plants facing the Antarctic stressful habitat.

Oxalic acid (OA) is considered as an important pathogenetic factor of some destructive diseases caused by some fungal pathogens such as Sclerotinia sclerotiorum. Oxalate degradation is important for plant health, and plants that contain oxalate oxidase (OXO) enzymes could breakdown oxalate into CO2 and H2O2, which subsequently evokes defense responses. However, some species, such as Arabidopsis thaliana, have no oxalate oxidase activity identified to date. The present study aims to develop transgenic Arabidopsis expressing a wheat oxalate oxidase, to test for the response to OA exposure and fungal infection by S. sclerotiorum. The results showed that the transgenic Arabidopsis lines that expressed the wheat OXO exhibited enhanced resistance to OA exposure and S. sclerotiorum infection in the tolerance assays. In the same manner, it could convert OA to CO2 and H2O2 to a higher extent than the wild-type. Intensive osmotic adjustments were also detected in the transgenic Arabidopsis lines. The higher level of produced H2O2 subsequently induced an elevated activity of antioxidant enzymes including superoxide dismutase (SOD) and peroxidase (POD) in the transgenic Arabidopsis plants. The present study indicated that the expression of a gene encoding wheat OXO could induce intensive osmotic adjustments and hydrogen peroxide related defense response, and subsequently increased tolerance to S. sclerotiorum in transgenic A. thaliana.

Germin and germin-like proteins (GLPs) are a broad and diverse family of developmentally regulated proteins widely distributed in plants. Oryza sativa L. harbours a large family of GLPs and serves as a good model for their study. In the present study, a germin-like protein gene (OsRGLP1) of rice origin was characterized by its heterologous expression in tobacco. The real-time PCR established almost a uniform expression of OsRGLP1 in leaves, stem, and roots of T1 Nicotiana tabacum cv. Samsun. Although no morphological difference was apparent between T0 transgenic and wild-type plants, leaves of mature transgenic plants showed necrotic lesions associated with an elevated content of H2O2, which was evidenced by in situ 3,3'-diaminobenzidine staining. A significantly higher activity of heat resistant superoxide dismutase (SOD) was observed in the transgenic plants as compared to the wild-type. The SOD activity in the transgenic plants was insensitive to potassium cyanide and sensitive to H2O2.

Four oxalate degrading endophytic bacteria were isolated from oxalate rich Colocasia esculenta tubers. Based upon the oxalate oxidase (EC 1.2.3.4) activity produced in nutrient medium, one bacterium was selected and identified as Ochrobactrum intermedium by 16S rDNA sequencing. Studies on effect of nutritional and non-nutritional parameters showed that oxalate oxidase production is inducible, requires Manganese ions in the medium, and very low fill-up volume is beneficial. Shake flask fermentation carried out with medium comprising Sucrose, Ammonium chloride, Sodium oxalate along with basal salts gave 0.5 UmL-1 oxalate oxidase activity and 0.454 Umg-1specific activity after 65h of fermentation. [ABSTRACT FROM AUTHOR]

Typha angustifolia L. (Typhaceae) is an emergent aquatic plant, and aerenchyma is formed through cell lysis in its leaves. The developing aerenchyma of T. angustifolia contains many CaOx crystals (raphides). Oxalate oxidase (OXO) (oxalate : oxygen oxidoreductase, EC1.2.3.4) can degrades calcium oxalate to carbon dioxide and hydrogen peroxide (H2O2). High level of H2O2 acts as a key inducer for different types of developmentally and environmentally programmed cell death (PCD) and can promote the formation of aerenchyma. Therefore, the objective of this study was to describe the relationship between aerenchyma formation and the degradation of CaOx crystals. Light and transmission electron microscopy (TEM) results showed that CaOx crystals occurred between PCD-susceptible cells in the early phase of aerenchyma formation, and those cells and CaOx crystals were degraded at aerenchyma maturation. Cytochemical localisation was used to detect H2O2, and H2O2 was found in crystal idioblasts. In addition, the oxalate content, H2O2 content and OXO activity were determined. The results showed that the concentration of oxalate was the highest in the third cavity formation stage and the H2O2 concentration was also highest at this stage. Meanwhile, the activity of OXO was also high in the third cavity formation stage. TpOXO was highly expressed during the CaOx crystal degradation period by quantitative real-time PCR analysis. These results show that the degradation of CaOx crystals is involved in the regulation of the PCD process of aerenchyma. This study will contribute to understanding the changes in CaOx crystals during the formation of aerenchyma in T. angustifolia. [ABSTRACT FROM AUTHOR]

Enzyme therapeutics have great potential for the treatment of systemic disorders such as urolithiasis and nephrocalcinosis, which are caused by the excessive accumulation of oxalate. However, exogenous enzymes have short half-lives in vivo and elicit high immunogenicity, which largely limit the therapeutic outcomes. Herein, we report a delivery strategy whereby therapeutic enzymes are encapsulated within a thin zwitterionic polymer shell to form enzyme nanocapsules. The strategy is exemplified by the encapsulation of oxalate oxidase (OxO) for the treatment of hyperoxaluria, because as-synthesized OxO nanocapsules have a prolonged blood circulation half-life and elicit reduced immunogenicity. Our design of enzyme nanocapsules that enable the systemic delivery of therapeutic enzymes can be extended to various biomedical applications. [ABSTRACT FROM AUTHOR]

Manganese (Mn) is an essential micronutrient with many functional roles in plant metabolism. Manganese acts as an activator and co-factor of hundreds of metalloenzymes in plants. Because of its ability to readily change oxidation state in biological systems, Mn plays and important role in a broad range of enzyme-catalyzed reactions, including redox reactions, phosphorylation, decarboxylation, and hydrolysis. Manganese(II) is the prevalent oxidation state of Mn in plants and exhibits fast ligand exchange kinetics, which means that Mn can often be substituted by other metal ions, such as Mg(II), which has similar ion characteristics and requirements to the ligand environment of the metal binding sites. Knowledge of the molecular mechanisms catalyzed by Mn and regulation of Mn insertion into the active site of Mn-dependent enzymes, in the presence of other metals, is gradually evolving. This review presents an overview of the chemistry and biochemistry of Mn in plants, including an updated list of known Mn-dependent enzymes, together with enzymes where Mn has been shown to exchange with other metal ions. Furthermore, the current knowledge of the structure and functional role of the three most well characterized Mn-containing metalloenzymes in plants; the oxygen evolving complex of photosystem II, Mn superoxide dismutase, and oxalate oxidase is summarized.

Being sessile organisms, plants are continuously challenged by phytopathogenic fungi, contributing the largest share in loss due to plant disease. Plants naturally possess a well-developed and programmed protein-based defense system, capable of producing antimicrobial cationic peptides to ward off pathogen attack. Numerous genes encoding antifungal proteins have been isolated, cloned, sequenced and transgenically expressed against multiple phytopathogenic fungi successfully. Genetic engineering technology has been widely utilized to produce transgenic plants with enhanced resistance against pathogens. Pathogenesis-related proteins (PR-proteins) is a group of the most important inducible defense-related antifungal proteins, including defensins, thionins, osomtin-like proteins, thaumatin-like proteins, chitinases, glucanases, oxalate oxidase or oxalate oxidase-like proteins and lipid transfer proteins. Transgenic plants have been developed by imparting the artificial expression of genes encoding antifungal PR-proteins. The expression of transgenes belonging to a single group of PR-proteins or synergistic action of transgenes from different groups has greatly uplifted the level of defense response in plants against fungi. Transgenic expression of antifungal PR-proteins has led to remarkably enhanced resistance in transgenic plants. In this review, we have summarized the role of PR-proteins in plant defense against fungi and 15 years of success achieved so far to generate a variety of transgenic plants resistant against fungi through overexpression of transgenes from different groups of PR-proteins. [ABSTRACT FROM AUTHOR]

It was found that two cell-surface lectins isolated from the nitrogen-fixing soil bacterium Azospirillum brasilense Sp7 and from its mutant defective in lectin activity, A. brasilense Sp7.2.3 can stimulate rapid formation of hydrogen peroxide, associated with an increase in the activities of oxalate oxidase and peroxidase in the roots of wheat seedlings. The most advantageous and most rapidly induced pathway of hydrogen peroxide formation was the oxidation of oxalic acid by oxalate oxidase because in this case, a 10-min treatment of the roots with the lectins at 10 µg ml-1 was sufficient. The data from this study attest that the Azospirillum lectins can act as inducers of adaptation processes in the roots of wheat seedlings.

We studied changes in the concentrations of ascorbate and glutathione, composition of soluble phenolics, and activity of oxalate oxidase in 75-day-old Serbian spruce plants after exposure to 5 μM and 50μM cadmium for 6-48 h. The presence of OxOxactivity in a conifer species is here demonstrated for the first time. Both Cd concentrations induced a decrease of OxOxactivity in treated plants in comparison with the control at all sampling dates. The concentrations of reduced glutathione, its oxidized form, and reduced ascorbate in the plants decreased during 48-h treatment with cadmium. Among simple phenolics, only catechin increased significantly during Cd treatment.

Kochia sieversiana (Pall.) C.A. Mey. is a forage plant that can grow in extremely alkalinized grasslands at pH 10 or higher. Accumulation of a large amount of oxalic acid (OxA) is a primary characteristic of K. sieversiana. In our study, seedlings of K. sieversiana were exposed to the following conditions: non-stress, salinity (200 mM, a molar ratio of NaCl and NaSO 1:1), and alkali stress (200 mM, a molar ratio of NaHCO and NaCO 1:1). Growth, water content, content of organic acids (including OxA), Na, and K, and activities of some OxA metabolism-related enzymes were determined. Results show that glycolate oxidase was the key enzyme for OxA synthesis; however, the carboxylation of phospho enolpyruvate (PEP) by PEP carboxylase (PEPC) probably played a minor role in the OxA-synthetic pathway. The pathway of L-ascorbic acid catabolism was not the main source of OxA accumulation, and the activity of oxalate oxidase (OxO) involved in OxA decomposition was not a limiting factor for inner OxA accumulation. Taken together, accumulation of a large amount of OxA are not related to the degradation and secretion function of OxO but largely depend upon its synthetic function. [ABSTRACT FROM AUTHOR]

Oxalate oxidase (EC 1.2.3.4) catalyzes the oxidative cleavage of oxalate to carbon dioxide with the reduction of molecular oxygen to hydrogen peroxide. Oxalate oxidase found its application in clinical assay for oxalate in blood and urine. This study describes the purification and biochemical characterization of an oxalate oxidase produced from an endophytic bacterium, Ochrobactrum intermedium CL6. The cell-free fermentation broth was subjected to two-step enzyme purification, which resulted in a 58.74-fold purification with 83% recovery. Specific activity of the final purified enzyme was 26.78 U mg−1 protein. The enzyme displayed an optimum pH and temperature of 3.8 and 80°C, respectively, and high stability at 4–80°C for 6 h. The enzymatic activity was not influenced by metal ions and chemical agents (K+, Na+, Zn2+, Fe3+, Mn2+, Mg2+, glucose, urea, lactate) commonly found in serum and urine, with Cu2+ being the exception. The enzyme appears to be a metalloprotein stimulated by Ca2+ and Fe2+. Its Km and Kcat for oxalate were found to be 0.45 mM and 85 s−1, respectively. This enzyme is the only known oxalate oxidase which did not show substrate inhibition up to a substrate concentration of 50 mM. Thermostability, kinetic properties, and the absence of substrate inhibition make this enzyme an ideal candidate for clinical applications. [ABSTRACT FROM AUTHOR]

The success of the necrotrophic fungus Sclerotinia sclerotiorum is largely dependent on its major virulence factor, oxalic acid ( OA). Virulence is lost in transgenic plants that express OA degrading enzymes, e.g. oxalate oxidase (OxO). The histopathology of S. sclerotiorum infection and OA accumulation was examined in a transgenic soybean line over-expressing OxO (OxO- OE) and its isogenic parent ( WT). In situ flower inoculation showed that the OxO- OE plants were highly resistant to the pathogen while the WT parents were susceptible. This difference in resistance was not apparent in the floral tissues, as aggressive hyphal activity was similar on both hosts, showing that high OxO activity and low OA accumulation in OxO- OE was not a deterrent. However, the process of fungal infection on excised leaf tissue differed on the two hosts. Primary lesions developed and showed similar severe ultrastructural damage on both hosts but rapid lesion expansion (colonization) proceeded only on the WT, concomitant with OA accumulation. Oxalic acid rose in OxO- OE 1 day post-inoculation and did not change over the following 3 days, showing that colonization can be blocked by maintaining low levels of OA. However, OxO degradation of OA did not deter initial host penetration and primary lesion formation. This shows that OA, the major virulence factor of S. sclerotiorum, is critical for host colonization but may not be required during primary lesion formation, suggesting that other factors are contributing to the establishment of the primary lesion. [ABSTRACT FROM AUTHOR]