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Xanthine

About: Xanthine is a research topic. Over the lifetime, 4046 publications have been published within this topic receiving 129820 citations. The topic is also known as: Xanthine.


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Journal ArticleDOI
TL;DR: An efficient electrochemical sensor for simultaneous electrochemical sensing of three purine compounds, uric acid (UA), xanthine (X) and hypoxanthine(HX), using a graphitized mesoporous carbon (GMC) modified glassy carbon electrode (GCE/GMC), has been demonstrated in pH 7 phosphate buffer solution without any enzyme, prior to electrode activation, surfactant and sample pre-concentration step as discussed by the authors.
Abstract: An efficient electrochemical sensor for simultaneous electrochemical sensing of three purine compounds, uric acid (UA), xanthine (X) and hypoxanthine (HX), using a graphitized mesoporous carbon (GMC) modified glassy carbon electrode (GCE/GMC) has been demonstrated in pH 7 phosphate buffer solution without any enzyme, prior to electrode activation, surfactant and sample pre-concentration step. Electrochemical investigation of the GCE/GMC with [Fe(CN)6]3− indicates metallic conductor like surface features of the modified electrode. A diffusion controlled reaction mechanism was identified for the electro-oxidation of the three purine compounds with an electrocatalytic pathway, except for the UA, where it shows a surface area effect with a mixed-diffusion and adsorption controlled mechanism at higher scan rates (>70 mV s−1). Calculated full-width of the half maximum values for the simultaneous detection of the three purine compounds are 42, 53 and 64 mV respectively and these are the lowest values ever reported in the literature, suggesting effective electron-transfer behaviour of the modified electrode for the purine oxidations. Calibration plots for the simultaneous detection of the purine compounds were linear in the concentration range of 20–400 μM, 20–320 μM and 20–240 μM for UA, X and HX with detection limit values of 110 nM, 388 nM, and 351 nM respectively. Selective sensing of the purine compounds in human blood-plasma, urine and fish samples was successfully demonstrated with recovery values ∼100%.

51 citations

Journal ArticleDOI
R F Bruns1, J H Fergus1
TL;DR: From literature data on functional activity, it is apparent that useful adenosine antagonist activity in‐vivo is only seen in compounds with solubility/affinity ratios greater than 100.
Abstract: The practical use of many adenosine receptor antagonists is limited by poor aqueous solubility. In some cases, solubilities are so low that they are difficult to measure by conventional means. To determine solubilities of adenosine antagonists, a sensitive radioreceptor method has been developed. Solubilities in Tris buffer (pH 7.7) ranged from 141 nM for 8-(2-amino-4-chlorophenyl)-1,3-dipropylxanthine to 945 microM for the amino-substituted xanthine PD 113,297. Ratios between solubility and adenosine receptor affinity varied from 15.8 for the A2-selective antagonist HTQZ to 169,000 for PD 113,297. From literature data on functional activity, it is apparent that useful adenosine antagonist activity in-vivo is only seen in compounds with solubility/affinity ratios greater than 100.

51 citations

Journal ArticleDOI
TL;DR: Results indicate that leaves of Camellia ptilophylla exhibit unusual purine alkaloid metabolism as they have the capacity to synthesize theobromine from adenine nucleotides, but they lack adequate methyltransferase activity to convert of theobomine to caffeine in detectable quantities, and the leaves have a capacity to convert xanthine to theobroma, probably via 3-methylxanthine.
Abstract: The biosynthesis and metabolism of purine alkaloids in leaves ofCamellia ptilophylla (cocoa tea), a new tea resource in China, have been investigated. The major purine alkaloid was theobromine, with theophylline also being present as a minor component. Caffeine was not accumulated in detectable quantities. Theobromine was synthesized from [8-14C] adenine and the rate of its biosynthesis in the segments from young and mature leaves from flush shoots was approximately 10 times higher than that from aged leaves from 1-year old shoots. Neither cellfree extracts nor segments fromC. ptilophylla leaves could convert theobromine to caffeine. A large quantity of [2-14C] xanthine taken up by the leaf segments was degraded to14CO2 via the conventional purine catabolic pathway that includes allantoin as an intermediate. However, small amounts of [2-14C] xanthine were also converted to theobromine. Considerable amounts of [8-14C] caffeine exogenously supplied to the leaf segments ofC. ptilophylla was changed to theobromine. These results indicate that leaves ofC. ptilophylla exhibit unusual purine alkaloid metabolism as i) they have the capacity to synthesize theobromine from adenine nucleotides, but they lack adequate methyltransferase activity to convert of theobromine to caffeine in detectable quantities, ii) the leaves have a capacity to convert xanthine to theobromine, probably via 3-methylxanthine.

51 citations

Journal ArticleDOI
TL;DR: Substrate specificity studies indicate two types of enzyme distributed among the bacteria along taxonomic lines, although other features indicate diversity of the enzyme within these two major groups.
Abstract: A diverse collection of xanthine-metabolizing bacteria was examined for xanthine-, 1-methylxanthine-, and 3-methylxanthine-oxidizing activity. Both particulate and soluble fractions of extracts from aerobically grown gram-negative bacteria exhibited oxidation of all three substrates; however, when facultative gram-negative bacteria were grown anaerobically, low particulate and 3-methylxanthine activities were detected. Gram-positive and obligately anaerobic bacteria showed no particulate activity or 3-methylxanthine oxidation. Substrate specificity studies indicate two types of enzyme distributed among the bacteria along taxonomic lines, although other features indicate diversity of the enzyme within these two major groups. The soluble and particulate enzymes from Pseudomonas putida and the enzyme from Arthrobacter S-2 were examined as type examples with a series of purine and analogues differing in the number and position of oxygen groups. Each preparation was active with a variety of compounds, but the compounds and position attacked by each enzyme was different, both from the other enzymes examined and from previously investigated enzymes. The soluble enzyme from Pseudomonas was inhibited in a competitive manner by uric acid, whereas the Arthrobacter enzyme was not. This was correlated with the ability of Pseudomonas, but not Arthrobacter, to incorporate radioactivity from [2-14C]uric acid into cellular material.

51 citations

Journal ArticleDOI
TL;DR: Evidence is provided that guinea pig and rabbit liver aldehyde oxidase in the presence of its electron donors such as aldehydes or N-heterocyclic compounds functions as a sulfoxide reductase towards sulindac and other sulfoxide compounds and a new electron-transfer system is proposed consisting of these two flavoenzymes.

51 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202361
2022108
202157
202060
201961
201869