69-93-2Relevant articles and documents
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Horbaczewski
, p. 202,584 (1887)
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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.
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.
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.
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Horbaczewski
, p. 356 ()
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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.
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Horbaczewski
, p. 201 (1887)
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Hydrogen peroxide is the major oxidant product of xanthine oxidase
Kelley, Eric E.,Khoo, Nicholas K.H.,Hundley, Nicholas J.,Malik, Umair Z.,Freeman, Bruce A.,Tarpey, Margaret M.
, p. 493 - 498 (2010)
Xanthine oxidase (XO) is a critical source of reactive oxygen species (ROS) in inflammatory disease. Focus, however, has centered almost exclusively on XO-derived superoxide (O2?-), whereas direct H2O2 production from XO has been less well investigated. Therefore, we examined the relative quantities of O2?- and H2O2 produced by XO under a range (1-21%) of O2 tensions. At O2 concentrations between 10 and 21%, H2O2 accounted for ～75% of ROS production. As O2 concentrations were lowered, there was a concentration-dependent increase in H2O2 formation, accounting for 90% of ROS production at 1% O2. Alterations in pH between 5.5 and 7.4 did not affect the relative proportions of H2O2 and O2?- formation. Immobilization of XO, by binding to heparin-Sepharose, further enhanced relative H2O2 production by ～30%, under both normoxic and hypoxic conditions. Furthermore, XO bound to glycosaminoglycans on the apical surface of bovine aortic endothelial cells demonstrated a similar ROS production profile. These data establish H2O2 as the dominant (70-95%) reactive product produced by XO under clinically relevant conditions and emphasize the importance of H2O2 as a critical factor when examining the contributory roles of XO-catalyzed ROS in inflammatory processes as well as cellular signaling.
Structure-activity relationship of xanthones as inhibitors of xanthine oxidase
Zhou, Ling-Yun,Peng, Jia-Le,Wang, Jun-Ming,Geng, Yuan-Yuan,Zuo, Zhi-Li,Hua, Yan
, (2018/02/17)
Polygala plants contain a large number of xanthones with good physiological activities. In our previous work, 18 xanthones were isolated from Polygala crotalarioides. Extented study of the chemical composition of the other species Polygala sibirica led to the separation of two new xanthones-3-hydroxy-1,2,6,7,8-pentamethoxy xanthone (A) and 6-O--D-glucopyranosyl-1,7- dimethoxy xanthone (C)-together with 14 known xanthones. Among them, some xanthones have a certain xanthine oxidase (XO) inhibitory activity. Furthemore, 14 xanthones as XO inhibitors were selected to develop three-dimensional quantitative structure-activity relationship (3D-QSAR) using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models. The CoMFA model predicted a q2 value of 0.613 and an r2 value of 0.997. The best CoMSIA model predicted a q2 value of 0.608 and an r2 value of 0.997 based on a combination of steric, electrostatic, and hydrophobic effects. The analysis of the contour maps from each model provided insight into the structural requirements for the development of more active XO inhibitors.
Real-Time Monitoring of Enzyme-Catalysed Reactions using Deep UV Resonance Raman Spectroscopy
Westley, Chloe,Fisk, Heidi,Xu, Yun,Hollywood, Katherine A.,Carnell, Andrew J.,Micklefield, Jason,Turner, Nicholas J.,Goodacre, Royston
, p. 6983 - 6987 (2017/05/29)
For enzyme-catalysed biotransformations, continuous in situ detection methods minimise the need for sample manipulation, ultimately leading to more accurate real-time kinetic determinations of substrate(s) and product(s). We have established for the first time an on-line, real-time quantitative approach to monitor simultaneously multiple biotransformations based on UV resonance Raman (UVRR) spectroscopy. To exemplify the generality and versatility of this approach, multiple substrates and enzyme systems were used involving nitrile hydratase (NHase) and xanthine oxidase (XO), both of which are of industrial and biological significance, and incorporate multistep enzymatic conversions. Multivariate data analysis of the UVRR spectra, involving multivariate curve resolution-alternating least squares (MCR-ALS), was employed to effect absolute quantification of substrate(s) and product(s); repeated benchmarking of UVRR combined with MCR-ALS by HPLC confirmed excellent reproducibility.
