Where is xanthine oxidase

Reoxidation of the molybdenum center occurs by electron transfer to the other redox-active centers of the enzyme, accompanied by deprotonation of the Mo-SH bond and displacement of bound product by hydroxide from solvent to regenerate the Mo-OH group. The oxidative hydroxylation of purine substrates takes place at the molybdenum center. The reaction is initiated by proton abstraction from the Mo-OH group by Glu, the active-site base, followed by nucleophilic attack on the carbon to be hydroxylated, and hydride transfer to the Mo-S double bond.

Suitable substrate orientation, overview. Arg is involved in stablizing the transition state in the course of nucleophilic attack, overview. Rhodobacter capsulatus. The oxidative hydroxylation of xanthine to uric acid takes place at the molybdenum center and results in the two-electron reduction of the metal from Mo VI to Mo IV.

Bacillus pumilus. Bacillus pumilus RL-2d. Biosynthesis of secondary metabolites , Caffeine metabolism , Drug metabolism - other enzymes , Purine metabolism. Enterobacter cloacae. NO generation occurs under aerobic conditions and is regulated by O2 tension, pH, nitrite, and reducing substrate concentrations. Drosophila melanogaster.

Capra hircus. Cavia porcellus. Equus asinus. Erythrocebus patas. Erythrocebus patas Patas monkey. Oryctolagus cuniculus. Desulfovibrio gigas. Enterobacter cloacae KY Felis catus. Lens culinaris. Locusta sp.

Triticum aestivum. Triticum aestivum Tugela DN. Ovis aries. Felis silvestris. Lontra longicaudis annectens. Mesocricetus auratus. The inhibition of XO by allopurinol is showed in Figure 1. Thus, XO inhibitors may be useful for treatment of many other diseases [ 41 , 42 ]. Among the many known XO inhibitors, allopurinol, oxypurinol, and febuxostat have been used widely for the treatment of hyperuricemia and gout [ 43 ]. XO inhibitors can act either at the purine binding site such as allopurinol [ 44 , 45 ] or at the FAD cofactor site such as benzimidazole [ 46 ].

XO inhibitors act by blocking the biosynthesis of uric acid from purine in the body [ 47 ] and it is believed that either increasing the excretion of uric acid or reducing the uric acid production helps to reduce the risk of gout [ 48 ]. Isolation of XO, as the widespread enzymes among different species, involves the extraction of the enzyme from a wide range of materials bacteria, milk, organs of different animals, etc. Therefore, all isolation methods use cream as the starting material; the cream is washed and churned to yield a crude MFGM preparation, dissociating and reducing agents are used to liberate XO from membrane lipoproteins, and some form of chromatography is used for purification [ 49 ].

Since the discovery of XO many authors tried to purify and characterize this enzyme. Schardinger [ 14 ] is a partially purified XO and found that reduced activity of the enzyme is not only a consequence of the removal of fat from milk, but also to reduce the concentration of the enzyme on the surface due to the absorption of fat molecules.

XO from milk was highly purified by Ball in [ 50 ]. He used continuous steps of centrifugation on milk in order to separate cream layer rich in XO. Ball [ 50 ] separated XO from cream. Since then, XO has been isolated and purified by several authors [ 51 , 52 ]. Hart and coworkers [ 53 ] prepared XO from milk according to the procedure described earlier by Palmer et al. They separated cream from milk and then added salicylate and EDTA as concentrated solutions to the cream.

The published purification procedures for xanthine oxidase include proteolytic cleavage, calcium chloride treatment, several ammonium sulfate fractionations, dialysis, and several chromatographic steps [ 55 , 56 ].

The suspension was centrifuged and the precipitate formed was discarded. Baghiani et al. Zhang et al. The Arthrobacter M3 culture was transferred into induction medium.

The cells were harvested by centrifugation and were resuspended in sodium phosphate. The most frequently used method for the determination of XO activity is described by Marcocci et al. The measurement is carried out in buffer pH 7. EDTA is often added to complexation of metals present in the test sample. The assay mixture always contains xanthine as a substrate and sample. Reaction is initiated by adding the XO.

Some studies support the hypothesis that uric acid is connected with elevated vascular events in patients with hypertension, diabetes, and known cardiovascular disease [ 60 — 63 ]. Allopurinol is XOI with high potential. Inhibitory activities of plant extracts and their constituents are compared with the activity of allopurinol as standard. In Table 1 is given the assay procedure of effect of plant extract on xanthine oxidase activity.

Xanthine oxidase inhibitors XOI are typically used in the treatment of nephropathy and renal stone diseases linked to hyperuricemia. There has been recent interest in the potential benefit of XOI in the prevention of vascular disease, because of emerging evidence suggesting a role for serum uric acid in the development of cardiovascular disease; the enzyme is an important source of oxidative stress in the vasculature [ 64 ].

XOI are agents that directly inhibit the synthesis of uric acid in vivo. Certain active constituents present in crude plant extracts like flavonoids and polyphenolic compounds have been reported to possess XOI [ 65 , 66 ]. These findings have opened the possibility of isolation of new natural compounds, which can be possible inhibitors of XO, and led to the growing interest in the investigation of medicinal plants. The activity of flavonoids as inhibitors of xanthine oxidase in vitro has been reported.

The absence of a hydroxyl group at C-3 enhances slightly the inhibition effect on XO [ 34 , 67 , 68 ]. In traditional medicine are used many herbs and their extracts in the treatment of various diseases that are the result of increased XO activity. Scientists have studied why some plants and their extracts have an inhibitory effect on the activity of XO Table 3 [ 69 ]. In Table 2 are given plant extract and pure compounds as potent XOI.

The structure-activity relationship of flavonoids as inhibitors of xanthine oxidase and as scavengers of the superoxide radical, produced by the action of the enzyme xanthine oxidase, was investigated. The hydroxyl groups at C-5 and C-7 and the double bond between C-2 and C-3 were essential for a high inhibitory activity on xanthine oxidase.

Flavones showed slightly higher inhibitory activity than flavonols [ 34 ]. This review is an overview of methods for the isolation and determination of XO activity in vivo and in vitro and inhibition by plant extracts and their constituents.

For isolation the most used methods are extraction, centrifugation, and chromatographic separation. Plant extracts and their constituents show good inhibitor activity and therefore may have a positive impact on the prevention of disease caused by increased activity of XO.

Xanthine oxidase inhibitors are agents that directly inhibit the synthesis of uric acid in vivo. Certain active constituents present in crude plant extracts like flavonoids and polyphenolic compounds have been reported to possess XOI. These findings have opened the possibility of isolation of new natural compounds, which can be potent inhibitors of XO, and led to the growing interest in the investigation of medicinal plants.

The authors declare that there is no conflict of interests regarding the publication of this paper. Financial support of this work is provided by the Serbian Ministry of Education and Science, Project no. ON This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors.

Read the winning articles. Journal overview. Special Issues. Academic Editor: Patricia Valentao. Received 18 Nov Accepted 21 Jan Published 23 Feb Abstract Xanthine oxidase XO is an important enzyme catalyzing the hydroxylation of hypoxanthine to xanthine and xanthine to uric acid which is excreted by kidneys.

Introduction Reactive oxygen species ROS such as hydrogen peroxide, superoxide radical anion, hydroxyl radical, alkylperoxyl radical, nitric oxide, and singlet oxygen are often associated with some physiopathological states in human. Scheme 1. Figure 1. Reference Tested sample Assay procedures [ 19 ] Erythrinastricta Roxb.

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