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PubMed1997

Inhibition of xanthine oxidase-xanthine-iron mediated lipid peroxidation by eugenol in liposomes.

The effect of eugenol on xanthine oxidase (XO) xanthine(X)-Fe+3-ADP mediated lipid peroxidation was studied in liver microsomal lipid liposomes. Eugenol inhibited the lipid peroxidation in a dose dependent manner as assessed by formation of thiobarbituric acid reactive substances. When tested for its effect on XO activity per se, (by measuring uric acid formation) eugenol inhibited the enzyme to an extent of 85% at 10 microm concentration and hence formation of O2.- also. However, the concentration of eugenol required for XO inhibition was more in presence of metal chelators such as EDTA, EGTA and DETAPAC, but not in presence of deferoxamine, ADP and citrate. The antiperoxidative effect of eugenol was about 35 times more and inhibition of XO was about 5 times higher as compared to the effect of allopurinol. Eugenol did not scavenge O2.- generated by phenazine methosulfate and NAD but inhibited propagation of peroxidation catalyzed by Fe2+ EDTA and lipid hydroperoxide containing liposomes. Eugenol inhibits XO-X-Fe+3 ADP mediated peroxidation by inhibiting the XO activity per se in addition to quenching various radical species.

Adenosine Diphosphate↗
PubMed1987

Effects of tannins on the oxidative damage of mouse ocular lens. I. Using the oxidative damage model induced by the xanthine-xanthine oxidase system.

The protective effects of various tannins on ocular lens against the induced oxidative damage were examined. Oxidative damage on mouse lenses was induced by incubating them with xanthine-xanthine oxidase, ADP and Fe3+ (X.XOD system). X.XOD system caused an increase in lipid peroxide of lens membrane and decreases in Na,K-ATPase and GSH reductase activities in the lenses. After pretreatment of lenses with X.XOD system, the lenses were incubated with tannins in the medium containing no X.XOD system and the effects of tannins on biochemical parameters in the lenses were determined. Higher molecular tannins (penta-O-galloyl-beta-D-glucopyranose and geraniin) decreased the lipid peroxide in the lens and restored GSH content, Na,K-ATPase and GSH reductase activities in the lens to the level comparable to control. However, all of tannins tested restored much insufficiently the cation level (ratio of Na+/K+) in the lens regardless of extents of restoration of Na,K-ATPase level by them. Because it was supposed that tannins might act primarily on the plasma membrane, the effect of tannins on lens plasma membrane was examined using cell free system. Lens was homogenated and separated into membrane pellet and supernatant. When the pellet was treated with X.XOD system, the lipid peroxide in the pellet increased and its Na,K-ATPase activity decreased. In addition, the treated pellet decreased the GSH level and GSH reductase activity in the supernatant, when the pellet was combined with the supernatant. Higher molecular tannins reduced lipid peroxide content in the X.XOD-treated pellet to control level and the pellet in which lipid peroxide content was reduced by tannins caused much less decreases of GSH level and GSH reductase activity in the supernatant. These results suggest that, in intact lens, higher molecular tannins act on plasma membrane to eliminate lipid peroxide produced by the X.XOD system and consequently suppress the decreases in both Na,K-ATPase and GSH reductase activities without their entering inside the cell.

Animals↗
PubMed1994

Blockade of platelet-mediated relaxation in rat aortic rings exposed to xanthine-xanthine oxidase.

Platelet-induced relaxation of endothelium-intact vascular tissues, mediated via release of endothelium-derived relaxing factor (EDRF), is diminished or lost after ischemia and reperfusion. Release of oxygen free radicals during ischemia-reperfusion may degrade EDRF and influence response of vascular tissues to platelets. To determine platelet modulation of tone of blood vessels treated with oxygen free radicals, rat aortic rings with intact endothelium were exposed to xanthine (X) plus xanthine oxidase (XO) 5 min before contraction with norepinephrine followed by exposure of rings to platelets. Treatment of aortic rings with X+XO caused a modest contraction, potentiated norepinephrine-mediated contraction, and inhibited platelet-mediated vasorelaxation. Exposure of aortic rings to X+XO also decreased ADP- as well as acetylcholine-mediated relaxation. Pretreatment of rings with superoxide dismutase or catalase did not change X+XO-induced inhibition of platelet-mediated relaxation, but it abolished the X+XO-induced contraction of rings as well as subsequent potentiation of norepinephrine-mediated contraction. Pretreatment of rings with hydroxyl radical scavengers dimethyl-2-thiourea, dimethyl sulfoxide, mannitol, or histidine attenuated the X+XO-induced inhibition of platelet-mediated relaxation, although these agents did not affect X+XO-induced contraction of rings. This study indicates that the vasoconstriction on exposure of aortic rings to X+XO is due to generation of superoxide anions, whereas inhibition of platelet-mediated relaxation after exposure of vessels to X+XO is due, at least in part, to release of hydroxyl radicals. Release of superoxide anions and hydroxyl radicals after temporary arterial occlusion may be the basis of subsequent modulation of vascular tone.

Animals↗
PubMed1985

Formation of antibodies to native DNA in rats after administration of native DNA treated with the xanthine-xanthine oxidase system.

The injection of native (double-stranded) deoxyribonucleic acid treated with the xanthine-xanthine oxidase system and emulsified with complete Freund's adjuvant into rats over a prolonged period of time induces the formation of antibodies to double-stranded DNA. The titer of antibodies was determined by an enzyme-linked immunosorbent assay (ELISA) in sera from treated animals. Control experiments using untreated native DNA or phosphate buffered saline likewise emulsified with Freund's Adjuvant showed only insignificant increases in titers of the antibody.

Animals↗
PubMed1996

Gold(I)-Purine Interactions: Synthesis and Characterization of Cyclic and Open Chain Polynuclear Gold(I) Complexes Containing Xanthine Derivatives and Bis(phosphine) as Bridging Ligands. Crystal Structures of [Au(2)(&mgr;-HX)(&mgr;-dmpe)].3H(2)O and [Au(2)(&mgr;-TT)(&mgr;-dmpe)].H(2)O (H(3)X = Xanthine; H(2)TT = 8-Mercaptotheophylline).

The reaction of [(AuBr)(2)(&mgr;-PR(2)P(CH(2))(n)()PR(2))] (where R = CH(3) for n = 1; R = Ph for n = 1, 3, 4) with N-alkylxanthine and thioxanthine derivatives, containing two ionizable protons in close positions, yields, under basic conditions, neutral heterobridged dinuclear gold(I) ring complexes [Au(&mgr;-L)(2)(&mgr;-PR(2)P(CH(2))(n)()PR(2))], which have been investigated by means of (1)H- and (31)P-NMR and FAB spectroscopies. Crystal structures of two of these complexes are reported. [Au(2)(&mgr;-HX)(&mgr;-dmpe)].3H(2)O (1) (H(3)X = xanthine; dmpe = 1,2-bis(dimethylphosphine)ethane) crystallizes in the monoclinic space group P2(1)/n with a = 9.348(2) Å, b = 8.656(2) Å, c = 24.585(5) Å, beta = 98.24(2) degrees, Z = 4, and R = 0.040. [Au(2)(&mgr;-TT)(&mgr;-dmpe)].H(2)O (2) crystallizes in the monoclinic space group P2(1)/n with a = 10.853(4) Å, b = 14.031(6) Å, c = 13.574(5) Å, beta = 100.80(4) degrees, Z = 4, and R = 0.063. The structures of 1 and 2 are similar and consist of dinuclear nine-membered ring molecules, in which the two linear two-coordinate gold atoms are bridged on one side by a dmpe ligand and on the other side by a bidentate xanthinato dianion, with intramolecular Au.Au distances of 3.053(1) and 2.952 (2) Å, respectively. In the former, the coordination of the xanthinato ligand to the gold atoms takes place through the N3 and N9 nitrogen atoms whereas, in the latter, N7,S8-chelate coordination of the 8-thiotheophyllinato dianion occurs. The magnitude of the Au.Au separation is analyzed in terms of the twisting of the xanthine derivative ligand from the plane containing the gold(I) and phosphorus atoms. For n = 6 the steric requirements of the Au(&mgr;-dpph)Au group prevents the formation of dinuclear ring complexes and open chain complexes are obtained. Finally, when the xanthine derivatives do not contain two close active coordination sites dinuclear open chain complexes are formed.

Journal Article↗
PubMed1994

The role of xanthine oxidase and xanthine dehydrogenase in skin ischemia.

The importance of sequential events which lead to skin necrosis has significant implications in trauma, vascular injury, and wound healing. In this series of experiments, we tested the hypothesis that xanthine oxidase (XO) activity was increased along an ischemic gradient of a skin flap and that the XO enzyme activity correlated with an increase in neutrophils. There were two animal groups in which the skin flaps were raised and assayed at 0, 1, or 6 hr. In the other group, they were created as bipedicle flaps for 7 days, before the distal attachment was divided and the tissue assayed. In the acutely raised flaps, some animals were treated with the XO inhibitor, allopurinol. Xanthine dehydrogenase (XD) and XO activity was measured with a fluorometric pterin assay and neutrophil concentration was measured using a myeloperoxidase marker. In this model, there was consistent skin necrosis in the distal end of the skin flap (48 +/- 8%). The data showed that both XD and XO activity in the distal ends was statistically significantly increased over the sham control or proximal ends of the skin flaps at 1 hr (P < 0.05). XO activity remained elevated in the distal ends at 6 hr. Allopurinol significantly reduced the neutrophil concentrations in the distal ends of the skin flaps when compared to untreated animals (P < 0.05). Moreover, allopurinol reduced skin necrosis to 12 +/- 1%. Preconditioning of the skin flap reduced the XO activity to sham control levels. The observations implicate XO activity as source of free radical injury in skin necrosis seen in random skin flaps.(ABSTRACT TRUNCATED AT 250 WORDS)

Allopurinol↗
PubMed2000

The impact of hepatic xanthine oxidase and xanthine dehydrogenase activities on liver function in chronic cholestasis.

Activities of hepatic xanthine oxidase (XO) and xanthine dehydrogenase (XD), serum liver enzymes, and reduced glutathione (GSH) were determined in livers of chronic cholestatic rats. The common bile duct was ligated (CBDL) and rats were randomized to either an untreated group or to treatment with allopurinol, a competitive XO inhibitor, or received a tungsten-supplemented diet to inactivate XO and XD, or received antioxidants vitamin C and vitamin E. One group underwent only sham laparotomy. After 4 weeks, in untreated CBDL animals serum aspartate aminotransferase and bilirubin concentrations were significantly elevated and hepatic GSH was significantly decreased when compared with the sham-operated group. Histochemical and enzymatic determinations of XD and XO showed a significant increase in hepatic XO activity after CBDL. Treatment with allopurinol and a tungsten-supplemented, molybdenum-free diet significantly attenuated serum liver enzymes, hepatic XO activity, and improved hepatic GSH levels, whereas vitamins C and E had a positive effect only on hepatic GSH levels. Our results support the hypothesis that cholestasis-induced hepatocellular injury is partially triggered by oxidative processes derived from increased hepatic XO activity. Inhibition and inactivation of XO exerts a hepatocellular protective effect in chronic cholestasis.

Allopurinol↗
PubMed1993

Conversion of xanthine dehydrogenase to xanthine oxidase during ischemia of the rat small intestine and the effect of trifluoperazine on the conversion.

The conversion from xanthine dehydrogenase (XD) to xanthine oxidase (XO) and the effect of trifluoperazine (TFP), a calmodulin inhibitor, on the conversion were examined during the normothermic ischemia of the rat small intestine. Rat jejunums were stored in lactated Ringer's solution (LR) at 37 degrees C for various hours after intravascular flushing with LR. The extents of the conversion from XD to XO (%XO) constituted 21.1% +/- 3.0%, 36.2% +/- 7.0%, 63.2% +/- 8.1%, and 88.2% +/- 8.6% after 0, 2, 4, and 6 hours of the preservation, respectively (control group). The preservation without the intravascular flushing showed significant increase in the %XO (99.5% +/- 6.0%) only after 6 hours compared with those in the control group (P < .05). When the intestines were stored in LR containing 50 mg/L of TFP at 37 degrees C, or stored in LR at 37 degrees C after the intraperitoneal pretreatment with 10 mg/kg of TFP 1 hour before laparotomy showed significant decrease in the extents of the conversion after 4 hours (P < .005) and 6 hours (P < .025) of the preservation, compared with those in the control group. When the dose of TFP for the pretreatment was increased to 50 mg/kg, the suppressive effect on the conversion was found even after 2 hours (P < .025) as well as after 4 hours (P < .005) and 6 hours (P < .025) of the preservation. These results suggest that TFP could be effective on reducing the XO-mediated postischemic reperfusion injury by means of inhibiting the conversion during ischemia of the rat small intestine.

Animals↗
PubMed1995

Conversion of xanthine dehydrogenase to xanthine oxidase in bovine carotid artery endothelial cells induced by activated neutrophils: involvement of adhesion molecules.

We have demonstrated that the endothelial cell-derived superoxide anion is deeply involved in the endothelial cell injury induced by activated neutrophils (Fujita, H., Morita, I. and Murota, S. (1994) Arch. Biochem. Biophys. 309, 62-69). To clarify the mechanism underlying the increase in the endothelial cell-derived superoxide anion induced by activated neutrophils, the conversion of xanthine dehydrogenase (XD) to xanthine oxidase (XO) in cultured endothelial cells isolated from bovine carotid arteries was investigated. Although the endothelial cells expressed both XD and XO activity, the XO activity of unstimulated cells comprised about 12% of the total (XD + XO) activity. When endothelial cells were exposed to neutrophils activated with phorbol 12-myristate 13-acetate (PMA), XO activity rapidly increased about 3-fold over the control. Whereas treatment of endothelial cells with PMA alone or unstimulated neutrophils alone did not increase the XO activity at all. The increase in XO activity in endothelial cells was also observed on the treatment of the cells with neutrophils activated with leukotriene B4 or thrombin. To determine whether or not proteases released from activated neutrophils are involved in the increased conversion of XD to XO in endothelial cells, the effects of the elastase specific inhibitor, ONO-5046, and protease inhibitors, such as aprotinin, gabexate mesylate and urinastatin, were examined. However, these protease inhibitors did not suppress the conversion of XD to XO induced by PMA-activated neutrophils. Moreover, the treatment of endothelial cells with purified human neutrophil elastase and H2O2 also did not affect the conversion at all. In contrast, monoclonal antibodies against CD11a and CD18 significantly inhibited the increased conversion of XD to XO induced by PMA-activated neutrophils. Moreover, tyrosine kinase inhibitors such as staurosporin and herbimysine also inhibited the increased conversion of XD to XO induced by PMA-activated neutrophils. These results indicate that the adhesion of activated neutrophils to endothelial cells via CD11a/CD18-ICAM-1 is involved in the conversion of XD to XO in endothelial cells induced by activated neutrophils.

Animals↗
PubMed1982

Enhanced production of hydroxyl radicals by the xanthine-xanthine oxidase reaction in the presence of lactoferrin.

The generation of hydroxyl radicals by the xanthine-xanthine oxidase reaction (C. Beauchamp and I. Fridovich (1970) J. Biol. Chem. 245, 4641-1616) has been shown to be increased by iron-saturated lactoferrin isolated from pig neutrophils. Hydroxyl radical production, measured by EPR spin trapping and by ethylene production from alpha-keto-gamma-methiol butyric acid, has been demonstrated to be produced by a Fenton-type Haber-Weiss reaction catalysed by lactoferrin. The possibility that lactoferrin catalyses such a reaction in vivo is considered.

Animals↗
PubMed2004

A Chinese herbal medicine Ermiao wan reduces serum uric acid level and inhibits liver xanthine dehydrogenase and xanthine oxidase in mice.

Ermiao wan, which is composed of phellodendri cortex and atractylodis rhizome, is described as eliminating heat, excreting dampness and anti-edema prescription in traditional Chinese medical literatures including Danxi's Experiences in Medicine and State Pharmacopoeia of People's Republic of China. So it is being used clinically in the treatment of gout and hyperuricemia in China. In the present study, the water extracts of Ermiao wan and phellodendri cortex at 840 and 480 mg/kg/day orally for 7 days were demonstrated to possess in vivo potent hypouricemic effects both in hyperuricemic mice pretreated with oxonate and in normal mice, respectively. In the hyperuricemic animals, the effect of Ermiao wan was equal to that of the reference drug allopurinol (at 10 mg/kg/day orally for 7 days), but in the normal mice, the former was weaker than latter. In addition, both Ermiao wan and phellodendri cortex were found to have in vivo relatively inhibitory effects on mouse liver xanthine dehydrogenase (XDH) and xanthine oxidase (XO) activities at the same dose described above. These inhibitory effects were weaker than that observed for allopurinol. Atractylodis rhizome at 340 mg/kg/day orally for 7 days did not show any effects on the above experiments. These results suggested that atractylodis rhizomes assisted and enhanced the effect of phellodendri cortex on reduction of serum uric acid level in hyperuricemic mice, and hypouricemic effects of Ermiao wan and phellodendri cortex may be achieved by other mechanism partly instead of the XDH and XO inhibition.

Administration, Oral↗
PubMed2005

Effects of cassia oil on serum and hepatic uric acid levels in oxonate-induced mice and xanthine dehydrogenase and xanthine oxidase activities in mouse liver.

We investigated the hypouricemic effects of cassia oil extracted from Cinnamomum cassia using hyperuricemic mice induced by potassium oxonate, and its inhibitory actions against liver xanthine dehydrogenase (XDH) and xanthine oxidase (XOD) activities. Oral administration of cassia oil significantly reduced serum and hepatic urate levels in hyperuricemic mice in a time- and dose-dependent manner. At doses of 450 mg/kg of cassia oil or above, serum urate levels of the oxonate-pretreated mice were not different from the normal control mice. Cassia oil at 600 mg/kg was found to be as potent as allopurinol, which reduced hepatic urate levels to lower than normal. In normal mice, urate levels in liver, but not in serum, were altered with dose-dependent decrease after cassia oil treatment. Furthermore, the ratio, liver uric acid/serum uric acid, was determined after cassia oil administration with time- and dose-dependent decreases in hyperuricemic mice. The positive dose-dependent decrease ratio was also observed after cassia oil treatment in the normal animals. The decreased extent of ratio elicited by cassia oil in normal mice appeared to be greater than that in the hyperuricemic animal. In addition, cassia oil significantly exhibited marked reductions in liver XDH/XOD activities, with an apparent dose-dependence in the normal and hyperuricemic mice. The onset of inhibition in enzyme activities elicited by allopurinol was much higher than that elicited by cassia oil. These results suggested that hypouricemic effects of cassia oil could be explained, at least partly, by inhibiting liver in vivo activities of XDH/XOD.

Administration, Oral↗
PubMed2000

N-ethylmaleimide inhibits xanthine oxidase activity with no detectable change in xanthine dehydrogenase activity in rabbit liver.

The effect of an alkylating agent, N-ethylmaleimide (NEM), on the activities of xanthine oxidase (XO) and xanthine dehydrogenase (XD) in the presence and absence of Cu2+ or trypsin in the cytosolic fraction from rabbit liver was examined. At concentrations ranging from 0.25 to 2.0 microM, allopurinol, which is generally considered to be a XO inhibitor, suppressed the XD activity (41.5-93.4% inhibition) in addition to the XO activity (28.6-88.4% inhibition) under basal conditions, without the addition of Cu2+ or trypsin. In contrast, NEM (100-400 microM) inhibited the XO activity (35.7-85.7% inhibition) without affecting the XD activity. Also, NEM inhibited the Cu2+- and trypsin-induced XO activities, but did not affect the XD activity at the same concentration range. These results demonstrate that NEM can be a selective inhibitor of XO activity in rabbit liver.

Allopurinol↗
PubMed1991

Kinetic comparison of reduction and intramolecular electron transfer in milk xanthine oxidase and chicken liver xanthine dehydrogenase by laser flash photolysis.

A comparative study using laser flash photolysis of the kinetics of reduction and intramolecular electron transfer among the redox centers of chicken liver xanthine dehydrogenase and of bovine milk xanthine oxidase is described. The photogenerated reductant, 5-deazariboflavin semiquinone, reacts with the dehydrogenase (presumably at the Mo center) in a second-order manner, with a rate constant (k = 6 x 10(7) M-1 s-1) similar to that observed with the oxidase [k = 3 x 10(7) M-1 s-1; Bhattacharyya et al. (1983) Biochemistry 22, 5270-5279]. In the case of the dehydrogenase, neutral FAD radical formation is found to occur by intramolecular electron transfer (kobs = 1600 s-1), presumably from the Mo center, whereas with the oxidase the flavin radical forms via a bimolecular process involving direct reduction by the deazaflavin semiquinone (k = 2 x 10(8) M-1 s-1). Biphasic rates of Fe/S center reduction are observed with both enzymes, which are due to intramolecular electron transfer (kobs approximately 100 s-1 and kobs = 8-11 s-1). Intramolecular oxidation of the FAD radical in each enzyme occurs with a rate constant comparable to that of the rapid phase of Fe/S center reduction. The methylviologen radical, generated by the reaction of the oxidized viologen with 5-deazariboflavin semiquinone, reacts with both the dehydrogenase and the oxidase in a second-order manner (k = 7 x 10(5) M-1 s-1 and 4 x 10(6) M-1 s-1, respectively). Alkylation of the FAD centers results in substantial alterations in the kinetics of the reaction of the viologen radical with the oxidase but not with the dehydrogenase. These results suggest that the viologen radical reacts directly with the FAD center in the oxidase but not in the dehydrogenase, as is the case with the deazaflavin radical. The data support the conclusion that the environments of the FAD centers differ in the two enzymes, which is in accord with other studies addressing this problem from a different perspective [Massey et al. (1989) J. Biol. Chem. 264, 10567-10573]. In contrast, the rate constants for intramolecular electron transfer among the Mo, FAD, and Fe/S centers in the two enzymes (where they can be determined) are quite similar.

Animals↗
PubMed1989

Conversion of xanthine dehydrogenase to xanthine oxidase as a possible marker for hypoxia in tumours and normal tissues.

The enzyme activities of endogenous xanthine dehydrogenase (XDH) and xanthine oxidase (XO) have been measured in 10 different types of mouse tumour and seven normal tissues. The conversion of XDH to XO has been observed in two tumour types upon the prolonged clamping off of the blood supply to the tumours. It is proposed that a similar conversion might also occur naturally in chronically hypoxic cells and that the ratio of the XO activity to the combined XO + XDH activities (%XO activity) could well serve as a marker for tissue hypoxia. A qualitative relationship exists between the %XO activity and literature values of the hypoxic fraction for some tumours measured by radiobiological assays. The influence of tumour size (about 0.2-1.8 g) on %XO activity is presented for all 10 tumours as well as %XO activity determinations for four of the normal tissues.

Animals↗
PubMed1978

pH-jump studies at subzero temperatures on an intermediate in the reaction of xanthine oxidase with xanthine.

Xanthine oxidase is stable and active in aqueous dimethyl sulphoxide solutions of up to at least 57% (w/w). Simple techniques are described for mixing the enzyme in this solvent at--82 degrees C, with its substrate, xanthine. When working at high pH values under such conditions, no reaction occurred, as judged by the absence of e.p.r. signals. On warming to--60 degrees C, for 10 min, however, the Very Rapid molybdenum(V) e.p.r. signal was obtained. This signal did not change on decreasing the pH, while maintaining the sample in liquid nitrate reductase, caused its molybdenum(V) e.p.r. signal to change from the high-pH to the low-pH form. These findings are not compatible with the conclusions of Edmondson, Ballou, Van Heuvelen, Palmer & Massey [J. Biol. Chem. (1973) 248, 6135-6144], that the Very Rapid signal is in prototropic equilibrium with the Rapid signal, and should be important in understanding the mechanism of action of the enzyme. They emphasize the unique nature of the intermediate represented by the Very Rapid e.p.r. signal. The possible value of the pK for loss of an exchangeable proton from the Rapid signal is discussed.

Chemical Phenomena↗
PubMed1989

Conversion of xanthine dehydrogenase to xanthine oxidase occurs during keratinocyte differentiation: modulation by 12-O-tetradecanoylphorbol-13-acetate.

The distributions of xanthine dehydrogenase (XD) and xanthine oxidase (XO) in subpopulations of murine keratinocytes differing in their stages of terminal differentiation were determined by enzymatic analyses. Keratinocytes were isolated from the skins of female SENCAR mice that had been treated 72 h earlier with either acetone or 12-O-tetradecanoylphorbol-13-acetate (TPA). The ratio of XO/(XD + XO) specific activities was used as an index of the XD to XO conversion. The XO/(XD + XO) ratios for basal cell, suprabasal cell, granular cell plus squamae, and horny sheet preparations isolated from acetone- or TPA-treated mice were 0.35, 0.35, 0.45, 0.75 and 0.28, 0.29, 0.58, and 1.0, respectively. Total XD + XO and XO specific activities in each subpopulation derived from TPA-treated mice were approximately twice the values measured in their control counterparts. Suspension culturing of basal cell keratinocytes in methylcellulose induced terminal differentiation and a conversion of XD to XO. The kinetics of keratin disulfide crosslinking and the XD to XO conversion were similar and preceded cornification. Collectively, these studies demonstrate that the conversion of XD to XO occurs primarily during the later stages of keratinocyte terminal differentiation. Furthermore, the increases in XO activity measured in epidermal homogenates after TPA treatment are due to TPA-dependent increases in 1) the relative proportions of keratinocytes undergoing differentiation, 2) tissue XD content, and 3) increased conversion of XD to XO.

Animals↗
PubMed1977

Distribution of xanthine oxidase and xanthine dehydrogenase specificity types among bacteria.

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.

Actinomycetales↗