Exogenous application of xanthine and uric acid and nucleobase-ascorbate transporter MdNAT7 expression regulate salinity tolerance in apple.

BACKGROUND: Soil salinity is a critical threat to global agriculture. In plants, the accumulation of xanthine activates xanthine dehydrogenase (XDH), which catalyses the oxidation/conversion of xanthine to uric acid to remove excess reactive oxygen species (ROS). The nucleobase-ascorbate transporter (NAT) family is also known as the nucleobase-cation symporter (NCS) or AzgA-like family. NAT is known to transport xanthine and uric acid in plants. The expression of MdNAT is influenced by salinity stress in apple. RESULTS: In this study, we discovered that exogenous application of xanthine and uric acid enhanced the resistance of apple plants to salinity stress. In addition, MdNAT7 overexpression transgenic apple plants showed enhanced xanthine and uric acid concentrations and improved tolerance to salinity stress compared with nontransgenic plants, while opposite phenotypes were observed for MdNAT7 RNAi plants. These differences were probably due to the enhancement or impairment of ROS scavenging and ion homeostasis abilities. CONCLUSION: Our results demonstrate that xanthine and uric acid have potential uses in salt stress alleviation, and MdNAT7 can be utilized as a candidate gene to engineer resistance to salt stress in plants.

Dual-Emission Reverse Change Ratio Photoluminescence Sensor Based on a Probe of Nitrogen-Doped Ti3C2 Quantum Dots@DAP to Detect H2O2 and Xanthine.

Titanium carbide quantum dots (Ti3C2 QDs) derived from two-dimensional (2D) Ti3C2Tx (MXene) are the rising-star material recently. Herein, nitrogen-doped Ti3C2 QDs (N-Ti3C2 QDs) were synthesized via a solvothermal method. The obtained N-Ti3C2 QDs exhibited excitation-dependent photoluminescence, antiphotobleaching, and dispersion stability. Furthermore, by combining the N-Ti3C2 QDs and DAP (2,3-diaminophenazine, the oxidative product of o-phenylenediamine) as a composite nanoprobe (N-Ti3C2 QDs@DAP), we developed a dual-emission reverse change ratiometric sensor to quantitatively monitor H2O2 based on photoinduced electron-transfer effects, where N-Ti3C2 QDs acted as the donor and DAP as the acceptor. On the basis of the xanthine converting into H2O2 through the catalysis of xanthine oxidase, the N-Ti3C2 QDs@DAP nanoprobe was also exploited for xanthine sensing. As a result, the proposed assay was demonstrated to be highly sensitive for H2O2 and xanthine with detection limits of 0.57 and 0.34 µM, respectively. In a word, we have investigated the application of N-Ti3C2 QDs in H2O2 and xanthine sensing and opened a new and exciting avenue for the N-Ti3C2 QDs in biosensing.

Simple and Cost-effective "Turn-on" Fluorescence Sensor for the Determination of Xanthine.

A simple and selective 'turn-on' fluorescence sensor have been developed for the determination of xanthine (XA) based on glutathione (GSH) capped copper nanoclusters (CuNCs) as the fluorescent probe. The proposed sensor possess several advantages such as sensitivity, short analysis time and requires no sample pretreatment. The conditions for the performances of the sensor have been optimized and good linear relationship was obtained between concentration and relative fluorescence intensity in the concentration range 9.0[Formula: see text]10-3 M to 8.0[Formula: see text]10-5 M with a detection limit 6.0[Formula: see text]10-6 M. The mechanism behind the fluorescence enhancement may be ascribed to the binding of XA on the surface of GSH CuNCs. The sensor have been successfully applied to determine XA in spiked physiological samples.

Hemin@carbon dot hybrid nanozymes with peroxidase mimicking properties for dual (colorimetric and fluorometric) sensing of hydrogen peroxide, glucose and xanthine.

The multifunctional hemin@carbon dot hybrid nanozymes (hemin@CD) with simultaneous peroxidase-like activity and fluorescence signalling property was prepared for the first time. Based on these properties, hemin@CD was applied to develop a dual-channel fluorescent probe for H2O2 and H2O2-based biocatalytic systems. By virtue of the peroxidase-like activity, hemin@CD can catalyze the oxidative coupling of 4-aminoantipyrine with phenol in the presence of H2O2 to form a pink-red quinoneimine dye with a maximum absorbance at 505 nm. Under the excitation wavelength of 480 nm, the green fluorescence of hemin@CD peaks at 540 nm and is quenched by the generated quinoneimine dye due to an inner filter effect, and also by H2O2 because of dynamic quenching. Thus, a colorimetric and fluorimetric dual-channel optical probe for H2O2 is obtained. Due to the glucose/xanthine transformations under formation of H2O2 by the relevant oxidase catalysis, the probe can be applied for detection of glucose and xanthine. The colorimetric detection limits for H2O2, glucose and xanthine are 0.11, 0.15, 0.11 µM, and the and fluorimetric detection limits are 0.15, 0.15, 0.12 µM, respectively. Graphical abstractSchematic representation of the colorimetric and fluorimetric dual probe for H2O2, glucose and xanthine based on the multifunctional emin@carbon dot) hybrid nanozymes with simultaneous peroxidase-like activity and fluorescence signalling property.

Convenient synthesis of three-dimensional hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide for non-enzymatic electrochemical sensing of xanthine.

A novel hybrid with three-dimensional (3D) hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide (CuS@Pd/N-RGO) has been prepared by a facile wet-chemical route without utilizing any template molecules and surfactants. The characterization results reveal that the 3D flower-like structure of CuS "core" is composed of interconnecting nanoplates, which is conductive to the loading of Pd nanoparticles' "shell" and results in the robust interaction between the core and shell for the formation of CuS@Pd cauliflowers. Anchoring such appealing CuS@Pd cauliflowers on the two-dimensional N-RGO can efficaciously inhibit the aggregation of CuS@Pd cauliflowers and accelerate the kinetics of xanthine oxidation. Benefiting from the multi-functional properties and unique morphology, the sensor constructed by CuS@Pd/N-RGO exhibits excellent performance for non-enzymatic detection of xanthine including a wide detection range of 0.7-200.0 µM (0.94 V vs. SCE), a low detection limit of 28 nM (S/N = 3), high reproducibility (relative standard deviation (RSD) = 4.1%), and commendable stability (retained 90% of the initial electrochemical responses after storage for 30 days), which is amongst the best of various electrochemical sensors reported for xanthine assays till date. Reliable and satisfying recoveries (95-105%, RSD ≤ 4.1%) are achieved for xanthine detection in real samples. The inspiring results make the uniquely structural CuS@Pd/N-RGO greatly promising in non-enzymatic electrochemical sensing applications. Graphical abstract A high-performance non-enzymatic xanthine sensor has been constructed by the three-dimensional hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide.

Bacterial Nucleobases Synergistically Induce Larval Settlement and Metamorphosis in the Invasive Mussel Mytilopsis sallei.

Marine bacterial biofilms have long been recognized as potential inducers of larval settlement and metamorphosis in marine invertebrates, but few chemical cues from bacteria have been identified. Here, we show that larval settlement and metamorphosis of an invasive fouling mussel, Mytilopsis sallei, could be induced by biofilms of bacteria isolated from its adult shells and other substrates from the natural environment. One of the strains isolated, Vibrio owensii MS-9, showed strong inducing activity which was attributed to the release of a mixture of nucleobases including uracil, thymine, xanthine, hypoxanthine, and guanine into seawater. In particular, the synergistic effect of hypoxanthine and guanine was sufficient for the inducing activity of V. owensii MS-9. The presence of two or three other nucleobases could enhance, to some extent, the activity of the mixture of hypoxanthine and guanine. Furthermore, we determined that bacteria producing higher concentrations of nucleobases were more likely to induce larval settlement and metamorphosis of M. sallei than were bacteria producing lower concentrations of nucleobases. The present study demonstrates that bacterial nucleobases play an important role in larval settlement and metamorphosis of marine invertebrates. This provides new insights into our understanding of the role of environmental bacteria in the colonization and aggregation of invasive fouling organisms and of the metabolites used as chemical mediators in cross-kingdom communication within aquatic systems.IMPORTANCE Invasive species are an increasingly serious problem globally. In aquatic ecosystems, invasive dreissenid mussels are well-known ecological and economic pests because they appear to effortlessly invade new environments and foul submerged structures with high-density aggregations. To efficiently control exotic mussel recruitment and colonization, the need to investigate the mechanisms of substrate selection for larval settlement and metamorphosis is apparent. Our work is one of very few to experimentally demonstrate that compounds produced by environmental bacteria play an important role in larval settlement and metamorphosis in marine invertebrates. Additionally, this study demonstrates that bacterial nucleobases can be used as chemical mediators in cross-kingdom communication within aquatic systems, which will enhance our understanding of how microbes induce larval settlement and metamorphosis of dreissenid mussels, and it furthermore may allow the development of new methods for application in antifouling.

Ultrafine Fe3C nanoparticles embedded in N-doped graphitic carbon sheets for simultaneous determination of ascorbic acid, dopamine, uric acid and xanthine.

A pyrolytic method is described for preparation of ultrafine Fe3C nanoparticles incorporated into N-doped graphitic carbon nanosheets (Fe3C@NGCSs). Iron phthalocyanine and graphitic carbon nitride (g-C3N4) are used as starting materials. The hybrid nanocomposite was placed on a glassy carbon electrode (GCE) and then applied to simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA) and xanthine (XA). Figures of merits are as follows: for AA, the linear response range covers the 54.0-5491.0 µM range, the lower detection limit is 16.7 µM, and the best working voltage (vs. the saturated calomel electrode (SCE)) is 0.05 V. The respective data for DA are 1.2-120.8 µM, 0.34 µM and 0.19 V (vs. SCE). For UA, the respective data are 4.8-263.0 µM, 1.4 µM and 0.32 V (vs. SCE), and for XA the data are 4.8-361.0 µM, 1.5 µM and 0.71 V (vs. SCE). The method was successfully applied to their simultaneous determination in spiked serum samples. Graphical abstract Ultrafine Fe3C nanoparticles embedded in N-doped graphitic carbon sheets for simultaneous determination of ascorbic acid, dopamine, uric acid and xanthine.

Recent progress in nanomaterial-based electrochemical and optical sensors for hypoxanthine and xanthine. A review.

This review (with 160 ref.) summarizes the progress that has been made in the methods for chemical or biochemical sensing of hypoxanthine and xanthine, which are produced as part of purine metabolism and are precursors of uric acid. An introduction discusses the importance of hypoxanthine and xanthine as analytes due to their significance in the clinical and food science, together with the conventional methods of analysis. A large section covers methods for the electrochemical hypoxanthine and xanthine sensing. It is divided into subsections according to the nanomaterials used including carbon nanomaterials, meal oxide nanoparticles, metal organic frameworks, conductive polymers, and bio-nanocomposites. A further large section covers optical methods for hypoxanthine and xanthine sensing, with subsections on nanomaterials including carbon nanomaterials, nanosheets, nanoclusters, nanoparticles, and their bio-nanocomposites. A concluding section summarizes the current status, addresses current challenges, and discusses future perspectives. Graphical abstractSchematic representation of the hypoxanthine and xanthine electrochemical and optical sensors incorporating various nanomaterials like graphene, carbon nanotubes (CNT), quantum dots (QD), nanoparticles and polymers, which are implemented in clinical and food analysis.

Inkjet-Printing Enzyme Inhibitory Assay Based on Determination of Ejection Volume.

An accurate, rapid, and cost-effective methodology for enzyme inhibitor assays is highly needed for large-scale screening to evaluate the efficacy of drugs at the molecular level. For the first time, we have developed an inkjet printing-based enzyme inhibition assay for the assessment of drug activity using a conventional inkjet printer composed of four cartridges. The methodology is based on the determination of the number of moles of the drug on the printed surface. The number of moles was quantified through the volume of substance ejected onto the printed surface. The volume ejected on the reaction spot was determined from the density of reagent ink solution and its weight loss after printing. A xanthine oxidase (XOD) inhibition assay was executed to quantitatively evaluate antioxidant activities of the drug based on the determination of the number of moles of the drug ejected by inkjet printing. The assay components of xanthine, nitro blue tetrazolium (NBT), superoxide dismutase (SOD)/drug, and XOD were printed systematically on A4 paper. A gradient range of the number of moles of SOD/drug printed on A4 paper could be successfully obtained. Because of the effect of enzyme activity inhibition, incrementally reduced NBT formazan colors appeared on the paper in a number-of-moles-dependent manner. The observed inhibitory mole (IM50) values of tested compounds exhibited a similar tendency in their activity order, compared to the IC50 values observed through absorption assay in well plates. Inkjet printing-based IM50 assessment consumed a significantly smaller reaction volume (by 2-3 orders of magnitude) and more rapid reaction time, compared to the well-plate-based absorption assay.

[Uroliths of dogs in Switzerland from 2003 to 2009]. / Urolithen von Hunden in der Schweiz von 2003 bis 2009.

Information on composition of uroliths collected between 2003 and 2009 from dogs in Switzerland and epidemiologic data of affected dogs are summarised in this paper. Of 490 stones analysed 44% were composed of calcium oxalate, 330% of struvite, 80% of silica, 7% of urate, 3% of cystine, 3% were mixed stones and 1% each were calcium phosphate and xanthine stones. Compared to other dogs, Norwich Terriers, Norfolk Terriers, Miniature Schnauzers, Miniature Pinscher and Yorkshire Terriers had a significantly increased risk to suffer from calcium oxalate stones, Dalmatians and Continental Bulldogs from urate stones and English Bulldogs from cystine stones. No breed had an increased risk of struvite or silica stones. Stones composed of silica were more prevalent in Switzerland compared to other countries and were more common in the eastern part than in the western part of Switzerland. This study shows that there are differences in occurrence and prevalence of uroliths between Switzerland and surveys of other countries.

A nanocomposite/crude extract enzyme-based xanthine biosensor.

A novel amperometric biosensor for xanthine was developed based on covalent immobilization of crude xanthine oxidase (XOD) extracted from bovine milk onto a hybrid nanocomposite film via glutaraldehyde. Toward the preparation of the film, a stable colloids solution of core-shell Fe3O4/polyaniline nanoparticles (PANI/Fe3O4 NPs) was dispersed in solution containing chitosan (CHT) and H2PtCl6 and electrodeposited over the surface of a carbon paste electrode (CPE) in one step. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used for characterization of the electrode surface. The developed biosensor (XOD/CHT/Pt NPs/PANI/Fe3O4/CPE) was employed for determination of xanthine based on amperometric detection of hydrogen peroxide (H2O2) reduction at -0.35V (vs. Ag/AgCl). The biosensor exhibited a fast response time to xanthine within 8s and a linear working concentration range from 0.2 to 36.0µM (R(2)=0.997) with a detection limit of 0.1µM (signal/noise [S/N]=3). The sensitivity of the biosensor was 13.58µAµM(-1)cm(-2). The apparent Michaelis-Menten (Km) value for xanthine was found to be 4.7µM. The fabricated biosensor was successfully applied for measurement of fish and chicken meat freshness, which was in agreement with the standard method at the 95% confidence level.

Amperometric biosensor for xanthine determination based on Fe3O4 nanoparticles.

An amperometric xanthine biosensor was developed based on the immobilization of xanthine oxidase (XO) into the Fe3O4 nanoparticles modified carbon paste. Electron transfer properties of unmodified and Fe3O4 nanoparticles modified carbon paste electrodes were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Fe3O4 nanoparticles increased electroactive surface area of the electrode and electron transfer at solution/electrode interface. Optimum pH, nanoparticle loading and enzyme loading were found to be 6.0; 14.2% and 0.6 Unit XO respectively. Fe3O4 nanoparticles modified carbon paste enzyme electrode allowed xanthine determination at -0.20 V, thus minimizing the potential interferences from electrochemically oxidizable substances such as ascorbic acid and uric acid. A linear relationship was obtained in the concentration range from 7.4 × 10-7 mol L-1 to 7.5 × 10-5 mol L-1 and a detection limit of 2.0 × 10-7 mol L-1. The biosensor was used for determination of xanthine in urine samples and the results indicate that the biosensor is effective for the detection of xanthine.

[Determination of four kinds of purines in deer fetus soft capsule by HPLC].

OBJECTIVE: To establish an HPLC method for simultaneous determination of four kinds of purines in deer fetus soft capsule. METHODS: Four kinds of purines were detected and determined by HPLC. The mobile phase was 0.02 mol/L KH2PO4 (containing 1 mmol/L heptane sulfonic acid sodium, pH = 3.8)-methanol = 97:3. Detection wavelength was 254 nm and flow rate was 1.5 ml min. The linear relationship of four kinds of purines was as follows: hypoxanthine: Y1 = 83695X1 + 355 (r1 = 0.9998), with the linear range 0.040-0.667 mg/mL; xanthine: Y2 = 50638X2 + 39 (r2 = 0.9989), with the linear range 0.008-0.119 mg/mL; guanine: Y3 = 30269X3-9562 (r3 = 0.9924), with the linear range 0.018 - 0.279 mg/mL; adenine: Y4 = 38975X4-8671 (r4 = 0.9989), with the linear range 0.027-0.399 mg/mL The average sample recovery rate of hypoxanthine, xanthine, guanine and adenine were 98.1%, 98.6%, 98.0% and 97.5%, with RSD 1.0%, 0.4%, 0.8% and 0.6%, respectively. RESULTS: The content of hypoxanthine, xanthine, guanine and adenine in 3 lots of deer fetus soft capsule were 116.5-132.0 microg/capsule, 21.2-23.0 microg/capsule, 48.6-54.3 microg/capsule and 68.9-75.2 microg/capsule, respectively. CONCLUSIONS: This method is simple,accurate and reproducible, which provides a basis for quality control of purines in deer fetus soft capsule.

Hydrophilic interaction liquid chromatography based method for simultaneous determination of purines and their derivatives in food spices.

This work presents method for separation and quantification of adenine, guanine, xanthine, hypoxanthine, uric acid, and creatinine in food spices using hydrophilic interaction liquid chromatography with UV detection. Optimized conditions allowed separation with mobile phases containing acetonitrile and additives ammonium acetate (90:10, v/v, pH 6.1) or formate (90:10, v/v, pH 3.2). In food spices no uric acid was detected, creatinine (16 ± 2 µg g-1) was found only in instant dried yeast. The highest content of purines was determined in dried yeast (xanthine 110 ± 8 µg g-1, hypoxanthine 441 ± 24 µg g-1, adenine 84 ± 16 µg g-1, guanine 163 ± 12 µg g-1), high in curry, herbal pepper, and chicken seasoning, the lowest concentration was in black pepper (hypoxanthine 12 ± 2 µg g-1, adenine 27 ± 3 µg g-1). To best of our knowledge, no such complementary method and obtained data have been reported so far.

Unveiling Xanthine Presence in Rohu Fish Using Ag+-Doped MoS2 Nanosheets Through Electrochemical Analysis.

Here, we envisage the development of the rapid, reliable, and facile electrochemical sensor for the primary detection of xanthine (Xn) which is significant for the food quality measurement, based on the silver-doped molybdenum disulfide (Ag@MoS2) nanosheets. The structural and compositional properties of the prepared samples were tested through X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photon spectroscopy (XPS). The two-dimensional (2D) MoS2 nanosheets provide the large surface area for the sensing applications and the silver ions help in the enhanced electrochemical response. The fabricated enzymatic biosensor exhibits magnificent cyclic stability with a limit of detection of 27 nM. Also, the sensor was tested for rapid, reproducible, specific, and regenerable up to 10 cycles and has a shelf life of 2 weeks. The outcomes of this study suggest that the proposed matrix could be employed for the fabrication of devices for early detection of xanthine.

Xanthine microsensor based on polypyrrole molecularly imprinted film modified carbon fiber microelectrodes.

A molecularly imprinted polymers (MIPs) microsensor was presented as a carbon fiber microelectrode (CFME) coating for specifically recognizing xanthine (Xan). The polymeric film was obtained based on the imprinted procedure of electropolymerization of pyrrole in the presence of the template molecule Xan by cyclic voltammetry, and template was removed by magnetic stirring. Under the optimum conditions, a satisfactory molecularly binding selectivity of Xan was obtained from the MIPs microsensor with an imprinting factor (IF) of 6.63 and a linear response to concentration in certain ranges. The ranges are from 4.0 × 10⁻6 to 6.0 × 10⁻5 M and from 8.0 × 10⁻5 to 2.0 × 10⁻³ M with a detection limit of 2.5 × 10⁻7 M. Meanwhile, good stability (relative standard deviation [RSD] = 3.2%, n = 10) and reproducibility (RSD = 2.0%, n = 10) were observed, and recoveries ranging from 96.9 to 102.5% were calculated when applied to Xan determination in real blood serum samples.

Amperometric detection of hypoxanthine and xanthine by enzymatic amplification using a gold nanoparticles-carbon nanohorn hybrid as the carrier.

A novel gold nanoparticles-single-walled carbon nanohorn (GNPs-SWCNH) hybrid was synthesized for the construction of an amperometric biosensing platform. The GNPs-SWCNH hybrid was stable in aqueous solution for at least two weeks, and was characterized with scanning electron microscopy, transmission electron microscopy, and electrochemical impedance spectroscopy. The average diameter of GNPs in situ synthesized on the SWCNH was 5-8 nm, and the good interaction between GNPs and SWCNH was confirmed by ultraviolet-visible absorption spectroscopy. The GNPs-SWCNH immobilized on a platinum electrode showed high electrochemical activity toward the oxidation of hydrogen peroxide and uric acid with low applied potentials. Combining with the enzymatic reaction of xanthine oxidase (XOx), a biosensor for hypoxanthine and xanthine was constructed. The XOx-GNPs-SWCNH-based biosensor exhibited good responses to hypoxanthine and xanthine with the linear ranges of 1.5 to 35.4 and 2.0 to 37.3 µM, and the detection limits of 0.61 and 0.72 µM, respectively. The recovery test showed acceptable results. The gold nanoparticles functionalized carbon nanohorns provided a promising way to construct an electrochemical platform for sensitive biosensing.

Amperometric determination of xanthine in fish meat by zinc oxide nanoparticle/chitosan/multiwalled carbon nanotube/polyaniline composite film bound xanthine oxidase.

Xanthine oxidase (XOD) was immobilized on a composite film of zinc oxide nanoparticle/chitosan/carboxylated multiwalled carbon nanotube/polyaniline (ZnO-NP/CHIT/c-MWCNT/PANI) electrodeposited over the surface of a platinum (Pt) electrode. A xanthine biosensor was fabricated using XOD/ZnO-NP/CHIT/c-MWCNT/PANI/Pt as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode connected through a potentiostat. The ZnO-NPs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the enzyme electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The biosensor showed optimum response within 4 s at 0.5 V potential, pH 7.0, 35 °C and linear range 0.1-100 µM with a detection limit of 0.1 µM. The enzyme electrode was employed for determination of xanthine in fish meat during storage. The electrode lost 30% of its initial activity after 80 uses over one month, when stored at 4 °C.

An amperometric biosensor for fish freshness detection from xanthine oxidase immobilized in polypyrrole-polyvinylsulphonate film.

A new amperometric biosensor was developed for determining hypoxanthine in fish meat. Xanthine oxidase with pyrrole and polyvinylsulphonate was immobilized on the surface of a platinum electrode by electropolymerization. The determination of xanthine-hypoxanthine was performed by means of oxidation of uric acid liberated during the enzyme reaction on the surface of the enzyme electrode at + 0.30V (SCE). The effects of pH, substrate concentration, and temperature on the response of the xanthine-hypoxanthine biosensor were investigated. The linear working range of the enzyme electrode was 1.0 × 10(-7) -1.0 × 10(-3) M of the hypoxanthine concentration, and the detection limit was 1.0 × 10(-7)M. The apparent K(m(app)) and I(max) of the immobilized xanthine oxidase were found to be 0.0154 mM and 1.203 µA/mM, respectively. The best pH and temperature value for xanthine oxidase were selected as 7.75 and 25°C, respectively. The sensor was used for the determination of hypoxhantine in fish meat. Results show that the fish degraded very rapidly after seven days and the hypoxanthine amount was found to increase over days of storage.

Xanthine nephrolithiasis in a galician blond beef calf.

A six-month-old female Galician Blond beef calf presented signs of apathy, anorexia and weight loss. The analysis of a blood sample confirmed renal failure. Bilateral nephrolithiasis was diagnosed at necropsy. Quantitative analysis revealed the nephroliths to be composed of 100 per cent xanthine. In cattle, xanthinuria has only been described in the Japanese Black breed, but never before in other breeds. Clinical history suggested a naturally occurring xanthinuria.