69-93-2Relevant articles and documents
The hunt for 8-oxoguanine deaminase
Hall, Richard S.,Fedorov, Alexander A.,Marti-Arbona, Ricardo,Fedorov, Elena V.,Kolb, Peter,Sauder, J. Michael,Burley, Stephen K.,Shoichet, Brian K.,Almo, Steven C.,Raushel, Frank M.
, p. 1762 - 1763 (2010)
(Chemical Equation Presented) An enzyme from Pseudomonas aeruginosa, Pa0142 (gi|9945972), that is able to catalyze the deamination of 8-oxoguanine (8-oxoG) to uric acid has been identified for the first time. 8-Oxoguanine is formed by the oxidation of guanine residues within DNA by reactive oxygen species, and this lesion results in G:C to T:A transversions. The value of k cat/Km for the deamination of 8-oxoG by Pa0142 at pH 8.0 and 30 ° C is 2.0 × 104 M-1 s-1. This enzyme can also catalyze the deamination of isocystosine and guanine at rates that are approximately an order of magnitude lower. The three-dimensional structure of a homologous enzyme (gi|44264246) from the Sargasso Sea has been determined by X-ray diffraction methods to a resolution of 2.2 A (PDB entry ). The enzyme folds as a (β/α)8 barrel and is a member of the amidohydrolase superfamily with a single zinc in the active site. This enzyme catalyzes the deamination of 8-oxoG with a kcat/K m value of 2.7 × 105 M-1 s-1. Computational docking of potential high-energy intermediates for the deamination reaction to the X-ray crystal structure suggests that active-site binding of 8-oxoG is facilitated by hydrogen-bond interactions from a conserved glutamine that follows β-strand 1 with the carbonyl group at C6, a conserved tyrosine that follows β-strand 2 with N7, and a conserved cysteine residue that follows β-strand 4 with the carbonyl group at C8. A bioinformatic analysis of available protein sequences suggests that ～200 other bacteria possess an enzyme capable of catalyzing the deamination of 8-oxoG. Copyright
Xanthine dehydrogenase electrocatalysis: Autocatalysis and novel activity
Kalimuthu, Palraj,Leimkühler, Silke,Bernhardt, Paul V.
, p. 2655 - 2662 (2011)
The enzyme xanthine dehydrogenase (XDH) from the purple photosynthetic bacterium Rhodobacter capsulatus catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid as part of purine metabolism. The native electron acceptor is NAD+ but herein we show that uric acid in its 2-electron oxidized form is able to act as an artificial electron acceptor from XDH in an electrochemically driven catalytic system. Hypoxanthine oxidation is also observed with the novel production of uric acid in a series of two consecutive 2-electron oxidation reactions via xanthine. XDH exhibits native activity in terms of its pH optimum and inhibition by allopurinol.
Mixed Inhibition of the Oxidoreductase Activity of Xanthine Oxidase by Pd2+ Ion
Sau, Apurba Kumar,Mondal, Madhu Sudan,Mitra, Samaresh
, p. 1547 - 1548 (1994)
Pd2+ ion shows 100percent inhibition of the oxidoreductase activity of xanthine oxidase, the nature of the inhibition being the uncommon mixed type (competitive-non-competitive); to our knowleage this is the first example of moxed inhibition of xanthine oxidase, and also of the fact that Pd2+ can act as an inhibitor of enzyme activity.
Low-potential amperometric enzyme biosensor for xanthine and hypoxanthine
Kalimuthu, Palraj,Leimkühler, Silke,Bernhardt, Paul V.
, p. 10359 - 10365 (2012)
The bacterial xanthine dehydrogenase (XDH) from Rhodobacter capsulatus was immobilized on an edge-plane pyrolytic graphite (EPG) electrode to construct a hypoxanthine/xanthine biosensor that functions at physiological pH. Phenazine methosulfate (PMS) was used as a mediator which acts as an artificial electron-transfer partner for XDH. The enzyme catalyzes the oxidation of hypoxanthine to xanthine and also xanthine to uric acid by an oxidative hydroxylation mechanism. The present electrochemical biosensor was optimized in terms of applied potential and pH. The electrocatalytic oxidation response showed a linear dependence on the xanthine concentration ranging from 1.0 × 10-5 to 1.8 × 10-3 M with a correlation coefficient of 0.994. The modified electrode shows a very low detection limit for xanthine of 0.25 nM (signal-to-noise ratio = 3) using controlled potential amperometry.
Tetrathiatriarylmethyl radical with a single aromatic hydrogen as a highly sensitive and specific superoxide probe
Liu, Yangping,Song, Yuguang,De Pascali, Francesco,Liu, Xiaoping,Villamena, Frederick A.,Zweier, Jay L.
, p. 2081 - 2091 (2012)
Superoxide (O2?-) plays crucial roles in normal physiology and disease; however, its measurement remains challenging because of the limited sensitivity and/or specificity of prior detection methods. We demonstrate that a tetrathiatriarylmethyl (TAM) radical with a single aromatic hydrogen (CT02-H) can serve as a highly sensitive and specific O 2?- probe. CT02-H is an analogue of the fully substituted TAM radical CT-03 (Finland trityl) with an electron paramagnetic resonance (EPR) doublet signal due to its aromatic hydrogen. Owing to the neutral nature and negligible steric hindrance of the hydrogen, O 2?- preferentially reacts with CT02-H at this site with production of the diamagnetic quinone methide via oxidative dehydrogenation. Upon reaction with O2?-, CT02-H loses its EPR signal and this EPR signal decay can be used to quantitatively measure O2?-. This is accompanied by a change in color from green to purple, with the quinone methide product exhibiting a unique UV-Vis absorbance (ε =15,900 M-1 cm-1) at 540 nm, providing an additional O2?- detection method. More than five-fold higher reactivity of CT02-H for O2?- relative to CT-03 was demonstrated, with a second-order rate constant of 1.7×104 M-1 s-1 compared to 3.1×103 M-1 s-1 for CT-03. CT02-H exhibited high specificity for O2?- as evidenced by its inertness to other oxidoreductants. The O2?- generation rates detected by CT02-H from xanthine/xanthine oxidase were consistent with those measured by cytochrome c reduction but detection sensitivity was 10- to 100-fold higher. EPR detection of CT02-H enabled measurement of very low O2?- flux with a detection limit of 0.34 nM/min over 120 min. HPLC in tandem with electrochemical detection was used to quantitatively detect the stable quinone methide product and is a highly sensitive and specific method for measurement of O2 ?-, with a sensitivity limit of ～2×10-13 mol (10 nM with 20-μl injection volume). Based on the O2-dependent linewidth broadening of its EPR spectrum, CT02-H also enables simultaneous measurement of O2 concentration and O2?- generation and was shown to provide sensitive detection of extracellular O 2?- generation in endothelial cells stimulated either by menadione or with anoxia/reoxygenation. Thus, CT02-H is a unique probe that provides very high sensitivity and specificity for measurement of O 2?- by either EPR or HPLC methods.
Bioluminescence Detection of Superoxide Anion Using Aequorin
Rahmani, Hossein,Ghavamipour, Fahimeh,Sajedi, Reza H.
, p. 12768 - 12774 (2019)
Although the superoxide anion (O2 -·) is generated during normal cellular respiration and has fundamental roles in a wide range of cellular processes, such as cell proliferation, migration, apoptosis, and homeostasis, its dysregulation is associated with a variety of diseases. Regarding these prominent roles in biological systems, the development of accurate methods for quantification of superoxide anion has attracted tremendous research attention. Here, we evaluated aequorin, a calcium-dependent photoprotein, as a potential bioluminescent reporter protein of superoxide anion. The mechanism is based on the measurement of aequorin bioluminescence, where the lower the concentration of coelenterazine under the oxidation of superoxide anion, the lower the amount aequorin regeneration, leading to a decrease in bioluminescence. The bioluminescence intensity of aequorin was proportional to the concentration of superoxide anion in the range from 4 to 40 000 pM with a detection limit (S/N = 3) of 1.2 pM, which was 5000-fold lower than those of the chemiluminescence methods. The proposed method exhibited high sensitivity and has been successfully applied to the determination of superoxide anion in the plant cell samples. The results could suggest a photoprotein-based bioluminescence system as a highly sensitive, specific, and simple bioluminescent probe for in vitro detection of superoxide anion.
Inhibition studies of bovine xanthine oxidase by luteolin, silibinin, quercetin, and curcumin
Pauff, James M.,Hille, Russ
, p. 725 - 731 (2009)
Xanthine oxidoreductase (XOR) is a molybdenum-containing enzyme that under physiological conditions catalyzes the final two steps in purine catabolism, ultimately generating uric acid for excretion. Here we have investigated four naturally occurring compounds that have been reported to be inhibitors of XOR in order to examine the nature of their inhibition utilizing in vitro steady-state kinetic studies. We find that luteolin and quercetin are competitive inhibitors and that silibinin is a mixed-type inhibitor of the enzyme in vitro, and, unlike allopurinol, the inhibition is not time-dependent. These three natural products also decrease the production of superoxide by the enzyme. In contrast, and contrary to previous reports in the literature based on in vivo and other nonmechanistic studies, we find that curcumin did not inhibit the activity of purified XO nor its superoxide production in vitro.
Effects of zinc acexamate (NAS-501) on superoxide radicals and lipid peroxidation of rat gastric mucosa
Tsutsui, Yasuhiro,Nakamura, Yukio,Yamaguchi, Shiho,Kawanaka, Nobuyo,Sato, Makoto
, p. 209 - 219 (1999)
Zinc acexamate (NAS-501), an anti-ulcer agent, has been reported to prevent various acute experimental gastric mucosal lesions and duodenal ulcers in rats. In order to clarify the mechanisms by which NAS-501 exhibits the anti-ulcer effects, we investigated the anti-oxidative effects of NAS-501 in vitro and in vivo. NAS-501 significantly reduced the superoxide radical-dependent chemiluminescence, generated by hypoxanthine-xanthine oxidase, rat neutrophils and guinea-pig macrophages in vitro. These in vitro effects were also confirmed by electron spin resonance using a 5,5-dimethyl-1-pyrroline-N-oxide spin-trapping method. In addition, NAS-501 significantly inhibited lipid peroxidation induced by increasing concentrations of Fe2+/ascorbate in rat gastric mucosal homogenate in vitro. Oral administration of NAS-501 (30 mg/kg) significantly inhibited production of thiobarbituric acid-reactive substance in rat gastric mucosa following per os instillation of 60% ethanol in 150 mmol/l HCI in vivo. These results suggest that NAS-501 exhibits the preventive effect from acute gastric mucosal lesions by the anti-oxidative activity.
Kinetic model of oxidation catalyzed by xanthine oxidase - The final enzyme in degradation of purine nucleosides and nucleotides
Banach, Kinga,Bojarska, Elzbieta,Kazimierczuk, Zygmunt,Magnowska, Lucyna,Bzowska, Agnieszka
, p. 465 - 469 (2005)
A new kinetic model is presented for analysis of experimental data of oxidation process catalyzed by milk xanthine oxidase. The kinetics for two substrates, xanthine and its analog 2-chloroadenine, in a broad pH range (5.8-9.0) are best described by an equation which is a rational function of degree 2:3 and 2:2, respectively. Copyright Taylor & Francis, Inc.
Inhibition of xanthine oxidase by flavonoids.
Nagao,Seki,Kobayashi
, p. 1787 - 1790 (1999)
Various dietary flavonoids were evaluated in vitro for their inhibitory effect on xanthine oxidase, which has been implicated in oxidative injury to tissue by ischemia-reperfusion. Xanthine oxidase activity was determined by directly measuring uric acid formation by HPLC. The structure-activity relationship revealed that the planar flavones and flavonols with a 7-hydroxyl group such as chrysin, luteolin, kaempferol, quercetin, myricetin, and isorhamnetin inhibited xanthine oxidase activity at low concentrations (IC50 values from 0.40 to 5.02 microM) in a mixed-type mode, while the nonplanar flavonoids, isoflavones and anthocyanidins were less inhibitory. These results suggest that certain flavonoids might suppress in vivo the formation of active oxygen species and urate by xanthine oxidase.
