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PubMed1990

Excretion of purine derivatives by ruminants: endogenous excretion, differences between cattle and sheep.

The endogenous urinary excretion of the purine derivatives allantoin, uric acid and xanthine plus hypoxanthine were measured in twenty-nine lambs, ten cattle (six steers, one cow and three preruminant calves) and four pigs. The sheep and mature cattle were nourished by intragastric infusion and the calves were given a milk-substitute. The pigs were fed on a purine-free diet. The excretion of total purine derivatives was substantially greater by the cattle, being 514 (SE 20.6) mumol/kg live weight (W)0.75 per d compared with 168 (SE 5.0) mumol/kg W0.75 per d by the sheep and 166 (SE 2.6) mumol/kg W0.75 per d by the pigs. Plasma from normally fed sheep, cows and pigs was incubated with either xanthine or uric acid. Sheep and pig plasma had no xanthine oxidase (EC 1.2.3.2) activity whereas plasma from cattle did. Uricase (EC 1.7.3.3) was not present in plasma of cattle and pigs and appeared to be present in trace amounts only in sheep plasma. It is suggested that the species differences in endogenous purine derivative excretion were probably due to the different profiles of xanthine oxidase activity in tissues and particularly in the blood. This is because a high xanthine oxidase activity would reduce the chance to recycle purines, by increasing the probability of degradation to compounds which could not be salvaged.

Allantoin↗

PubMed1994

A re-evaluation of the tissue distribution and physiology of xanthine oxidoreductase.

Xanthine oxidoreductase is an enzyme which has the unusual property that it can exist in a dehydrogenase form which uses NAD+ and an oxidase form which uses oxygen as electron acceptor. Both forms have a high affinity for hypoxanthine and xanthine as substrates. In addition, conversion of one form to the other may occur under different conditions. The exact function of the enzyme is still unknown but it seems to play a role in purine catabolism, detoxification of xenobiotics and antioxidant capacity by producing urate. The oxidase form produces reactive oxygen species and, therefore, the enzyme is thought to be involved in various pathological processes such as tissue injury due to ischaemia followed by reperfusion, but its role is still a matter of debate. The present review summarizes information that has become available about the enzyme. Interpretations of contradictory findings are presented in order to reduce confusion that still exists with respect to the role of this enzyme in physiology and pathology.

Animals↗

PubMed1986

Superoxide-dependent and -independent mechanisms of iron mobilization from ferritin by xanthine oxidase. Implications for oxygen-free-radical-induced tissue destruction during ischaemia and inflammation.

Xanthine oxidase is able to mobilize iron from ferritin. This mobilization can be blocked by 70% by superoxide dismutase, indicating that part of its action is mediated by superoxide (O2-). Uric acid induced the release of ferritin iron at concentrations normally found in serum. The O2(-)-independent mobilization of ferritin iron by xanthine oxidase cannot be attributed to uric acid, because uricase did not influence the O2(-)-independent part and acetaldehyde, a substrate for xanthine oxidase, also revealed an O2(-)-independent part, although no uric acid was produced. Presumably the amount of uric acid produced by xanthine oxidase and xanthine is insufficient to release a measurable amount of iron from ferritin. The liberation of iron from ferritin by xanthine oxidase has important consequences in ischaemia and inflammation. In these circumstances xanthine oxidase, formed from xanthine dehydrogenase, will stimulate the formation of a non-protein-bound iron pool, and the O2(-)-produced by xanthine oxidase, or granulocytes, will be converted by 'free' iron into much more highly toxic oxygen species such as hydroxyl radicals (OH.), exacerbating the tissue damage.

Ferritins↗

PubMed1989

Effects of 3,5,3'-triiodothyronine (T3) on rat liver peroxisomal compartment during cold exposure.

In this study, by enzymatic assays and morphometric-stereologic analyses, we show that the remodelling of the rat liver peroxisomal compartment, occurring during cold exposure, is largely influenced by the thyroid state of the animal. The research was performed both on the whole rat liver peroxisomal population and on 2 peroxisomal subpopulations: one having a diameter greater than 0.5 microns, sedimenting at 10,000 g and called Pe (Peroxisomes); and the other having a diameter less than 0.5 microns, sedimenting at 27,000 g and called sPe (small Peroxisomes). The increase in the peroxisome number and in the peroxisome volume densities, elicited by cold exposure, is greatly reduced in hypothyroid cold-exposed animals (-63% and -40% respectively, P less than 0.01), while triiodothyronine (T3) administration to these rats restores the values observed in normal cold-exposed animals. The "clusters" and the strict association between mitochondria and peroxisomes, more frequently found in cold-exposed rats, are rarely observed in hypothyroid cold-exposed animals. At peroxisomal enzymic level, the thyroid hormone inhibits, during cold exposure, the uricase activity (-29% in Pe and -40% in sPe), and stimulates the palmitoyl-coenzyme A oxidase activity (+44% in Pe and +88% in sPe). The results also demonstrate that T3 exerts all these effects by acting principally on sPe.

Animals↗

PubMed2005

An increase of uricogenesis in the Kuruma shrimp Marsupenaeus japonicus under nitrite stress.

Kuruma shrimp Marsupenaeus japonicus Bate, under the stress of 0.36 and 1.39 mM nitrite at 30 per thousand (parts per thousand, g kg(-1)) for 48 h, were examined for nucleotide-related compounds, specific activities of xanthine dehydrogenase (XDH), xanthine oxidase (XOD), and uricase. The levels of total nucleotide-related compounds, including xanthine and hypoxanthine, in the gill increased directly with ambient nitrite, whereas the levels of total nucleotide-related compounds, including xanthine and hypoxanthine, in the hepatopancreas were inversely related to ambient nitrite. Specific activity of XOD in the hepatopancreas increased directly with ambient nitrite, whereas no significant difference in uricase activity in the hepatopancreas was observed among three treatments. In another experiment, M. japonicus, following 48 h exposure to 0.36 and 1.39 mM nitrite, were examined for ammonia, urea, and urate levels in tissues. Hemolymph urea and exoskeleton urate levels increased directly with ambient nitrite, whereas hemolymph urate and exoskeleton urea levels were inversely related to ambient nitrite. It is concluded that M. japonicus exhibited uricogenesis and uricolysis, and an increase of uricogenesis occurred for the shrimp under nitrite stress. Urate produced in the hepatopancreas was transported and accumulated in the epidermis, and removed along with the exoskeleton at the time of molting.

Ammonia↗

PubMed1978

Isolation and biochemical properties of two types of microbody from Neurospora crassa cells.

Cells of the Neurospora crassa slime mutant grown in sucrose medium exhibited low activities of glyoxysomal marker enzymes isocitrate lyase (ICL), malate synthetase (MS), and malate dehydrogenase. Transfer of the cells to a medium containing acetate as sole carbon source ("acetate medium") induced a strong increase in the activities of these enzymes in both the soluble and the crude particulate cell fraction. Soluble isocitrate lyase activity increased rapidly after a lag phase of about 45 minutes. Addition of 0.1 mM cycloheximide to the acetate medium 3 hours after transfer of the cells halted the rise of isocitrate lyase activity in either cell fraction, but the inhibition of the incorporation of ICL activity into the particulate cell fraction was delayed by 1 hour. Addition of 20 g/l glucose resulted in the immediate decrease of both soluble and particulate ICL activities. Transfer to acetate medium induced no change in the activities of other microbody marker enzymes such as catalase, uricase or D-amino acid oxidase. Resolution of crude homogenates of "slime" cells by sucrose density gradient centrifugation yielded two major protein bands: A mitochondrial band at a density of 1.180 kg/l showing maximum activites of fumarase, isocitrate dehydrogenase and cytochrome c oxidase, and a microbody-rich band which obviously consisted of two types of organelles with different biochemical properties. Maximum activities of ICL and MS sedimented at a density of 1.21 kg/l while the peaks of particulate uricase and catalase activities were recovered at 1.24 kg/l.

Acetates↗

PubMed1975

Kinetic studies dealing with an immobilized bienzyme system.

The binding of enzymes into artificial membranes makes possible a study of the interaction between membrane structure and enzyme kinetics within a simple context. Artificial protein membranes bearing a bienzyme system (xanthine oxidase, uricase) are produced by using a co-crosslinking method. The inhibition of uricase was shown to be dependent not only on the concentration of inhibitor in the bulk solution, but also on the kinetic properties of the membrane-bound enzymes. In the presence of xanthine oxidase inside the structure the uricase inhibition by xanthine is less important than in solution. Under defined conditions the activity was found to be higher in the presence of inhibitor than in its absence. Due to diffusion limitations this specific bienzyme system is more efficient when immobilized inside a membrane than when in solution.

Binding, Competitive↗

PubMed1985

The effect of bezafibrate and long-chain fatty acids on peroxisomal activities in cultured rat hepatocytes.

Peroxisomal activities have been evaluated in cultured rat hepatocytes in the presence of bezafibrate or long-chain fatty acids added to the culture medium. All activities decreased continuously over a time period of 100 h in culture but selected activities were relatively increased as a function of the added effectors. This relative increase in peroxisomal activities was dose-dependent, discernible within the first 24 h in culture and consisted of activities related specifically to peroxisomal fatty acyl beta-oxidation, e.g., cyanide-insensitive palmitoyl-CoA oxidation, H2O2-forming palmitoyl-CoA oxidase and heat-labile enoyl-CoA hydratase. Peroxisomal catalase or mitochondrial fatty acyl beta-oxidation (cyanide-sensitive) remained relatively unchanged. The relative increase in peroxisomal activities was accompanied by a respective increase in the number of peroxisomes as well as in thymidine incorporation rate.

Animals↗

PubMed1993

[The postnatal development of porcine purine catabolism and the effect of the environmental temperature on turnover].

Experiments in piglets indicate that the catabolic metabolism of purines is only developed during the first 4 weeks of life. During this time the catalytic activity of uricase in liver homogenates is increased about 5.5 fold (p < 0.01). The counts of uricase-carrying peroxisomes and cores are increased to a similar degree (p < 0.01). In the same time the catalytic activity of cytosolic xanthine oxidase is elevated about 4.6 fold (p < 0.01), mainly in the second and third week. In blood plasma uric acid is decreased from 19 to 12 molar % during weeks 1 to 4, hypoxanthine, xanthine and allantoin remain relatively constant. In urine xanthine and uric acid are decreased, hypoxanthine and allantoin are increased. At the age of 2-3 days a decrease of ambient temperature from 32 to 20 degrees C caused an increase of the plasma pool (p < 0.01) and turnover (p < 0.05) of uric acid. Pool size and turnover of hypoxanthine are only slightly elevated. The results are discussed in view of the slow development of hepatic enzymes, the increase of uric acid pool at lowered ambient temperature and causal events leading to urate nephropathia.

Animals↗

PubMed1996

Biochemical and functional differences in rat liver mitochondrial subpopulations obtained at different gravitational forces.

Previous studies have reported that liver mitochondria may be fractionated into different subpopulations. However, no careful studies have been performed to exclude mitochondrial damage and to investigate more thoroughly the possible biochemical differences existing between the subpopulations. In this study, we analysed the integrity and the biochemical properties of rat liver mitochondria. Mitochondrial fractions were obtained by differential centrifugation at different gravitational forces: 1000 g (M1 fraction), 3000 g (M3 fraction) and 10,000 g (M10 fraction). The integrity of these organelles was checked by measuring citrate synthase activity both in the presence and absence of Triton X-100 detergent. Biochemical analyses included polarographic determination of cytochrome oxidase activity and respiratory parameters and spectrophotometric determination of cytochrome content. (1) The integrity of mitochondria was almost homogeneous between fractions (88.5, 80 and 78.3% in M1, M3 and M10 fractions, respectively). (2) The heaviest M1 fraction contains mitochondria which are on average twice as large as M3 and about three times as large as M10. (3) The M1 fraction exhibited the highest specific cytochrome oxidase activity (1040 +/- 20 n Atoms O/min x mg protein) and the highest respiratory rates (72 +/- 3 n Atoms O/min x mg protein and 526 +/- 45 n Atoms O/min x mg protein for States 4 and 3, respectively). Oxidative capacity and respiratory rates decreased as the size of the organelles decreased, reaching values of 1/5 and 1/14 in the M3 and M10 fractions as compared to the M1. (4) These changes are accompanied by a change in the respiratory control ratio (RCR), which varies from 7.3 in M1 to about 2.0 in M10. A similar trend was observed in cytochrome contents but the differences were not as great as cytochrome oxidase activity and State 3 respiration. These results, as a whole, show that a mitochondrial heterogeneity exists in rat liver cell. We suggest that the above-mentioned differences might represent steps of mitochondrial maturation. The maturation would be fundamentally based on the increase of efficiency of the mechanism for ATP synthesis.

Acid Phosphatase↗

PubMed2001

Synthesis and structure-activity relationships of 1-phenylpyrazoles as xanthine oxidase inhibitors.

A series of 1-phenylpyrazoles was evaluated for inhibitory activity against xanthine oxidase in vitro. Of the compounds prepared, 1-(3-cyano-4-neopentyloxyphenyl)pyrazole-4-carboxylic acid (Y-700) had the most potent enzyme inhibition and displayed longer-lasting hypouricemic action than did allopurinol in a rat model of hyperuricemia induced by the uricase inhibitor potassium oxonate.

Allopurinol↗

PubMed1990

Toxicological studies on a benzofurane derivative. II. Demonstration of peroxisome proliferation in rat liver.

The uricosuric drug benzbromarone (3,5-dibromo-4-hydroxyphenyl)-1-(2-ethyl-3-benzofuranyl)methanone, a benzofurane derivative, was studied for its effects on parameters related to hepatic peroxisome proliferation. Groups of male F-344 rats were fed either basal diet, the peroxisome proliferator clofibrate at 5000 ppm as a comparison compound, or benzbromarone at two doses, 1000 and 2000 ppm. Benzbromarone and clofibrate produced hepatomegaly and increases in the activities of catalase, acyl CoA oxidase, malate dehydrogenase, and glycerol-3-phosphate dehydrogenase. Benzbromarone and clofibrate also both induced similar histologic and ultrastructural changes in hepatocytes, including induction of peroxisomes. Therefore, benzbromarone acted as a peroxisome-proliferating agent in rats under these conditions. Benzbromarone differs from other peroxisome proliferators in its chemical structure, uricosuric action, and the morphology of liver peroxisomes that were induced by exposure.

Animals↗

PubMed1989

Morphological and functional modifications of rat liver peroxisomal subpopulations during cold exposure.

A report is made (during cold exposure) of: a) the morphometric-stereologic analysis both on the whole rat liver peroxisomal population, and on 2 peroxisomal subpopulations having a diameter greater than 0.5 microns, and less than 0.5 microns, called Pe (Peroxisomes) and sPe (small Peroxisomes), respectively; b) the uricase and palmitoyl-coenzyme A oxidase activity assay on 2 classes of rat liver peroxisomes, sedimenting at 10,000 g and 27,000 g and containing Pe and sPe, respectively. The peroxisomal volume and number densities increase during cold exposure, reaching a maximum (+67% and +130%, respectively, P less than 0.05) at 10 days. These modifications are accompanied by an appreciable reduction of the average peroxisome volume (from 0.27 +/- 0.05 microns 3 to 0.19 +/- 0.02 microns 3) due to a major percentage increase of sPe during cold exposure. At a qualitative level, the formation of "clusters" and a stricter association between mitochondria and peroxisomes is also observed. Cold exposure increases the oxidative capacity of the whole peroxisomal compartment; in the Pe fraction the palmitoyl-CoA oxidase and uricase specific activity ratio is constant (about 0.1), during cold exposure, but in the sPe fraction this ratio increases significantly (from 0.05 to 0.09). The results indicate that the peroxisomal population is influenced during cold exposure, with the formation of a new peroxisomal population which is on average smaller and more specialized for the beta-oxidative activity. The possible involvement of peroxisomes in thermoregulatory thermogenesis during cold exposure is also discussed.

Animals↗

PubMed1978

A purine N1-C6 hydrolase activity in the chicken egg yolk: a vestigial enzyme?

All attempts to prove the presence of xanthine oxidase and uricase in yolk preparations failed. We were able instead to show that yolk preparations could hydrolyze the N1-C6 bond of certain purine bases. In the case of xanthine, 4-ureido-imidazole-5-carboxylic acid and 4-ureido-imidazole are formed. Activity only becomes apparent during purification. An analogous enzyme was described earlier in Clostridium cyclindrosporum. The liver and the blood plasma of actively laying hens do not contain the enzyme. A scheme for the degradation of egg ribonucleic acids is presented.

Allantoin↗

PubMed1981

The application of a sensitive uricase-peroxidase couple reaction to a centrifugal fast analyser for the determination of uric acid.

A uricase-peroxidase coupled system, for the determination of uric acid, applied to a CentrifiChem-500 centrifugal fast analyser is described. Relatively large amounts of ascorbic acid, due to the inclusion of an ascorbate oxidase urine diluent, and hemoglobin appear not to interfere with the procedure while the incorporation of potassium ferrocyanide into the reagents has led to the near-total elimination of bilirubin interference. The incubation period is relatively short compared with other similar procedures and the one reagent system has made the procedure simple to perform. The use of sodium 2-hydroxy-3,5-dichlorobenzenesulfonate and 4-aminoantipyrene in the oxidative coupling reaction has incorporated the advantages of increased sensitivity, over phenol-4-aminoantipyrene systems, as well as the amenability of the reagent towards lyophilization or "dry-fill".

Ampyrone↗

PubMed1994

A sensitive determination of uric acid in serum using uricase/catalase/formaldehyde dehydrogenase coupled with formate dehydrogenase.

We developed and evaluated an assay for serum uric acid based on the uricase (EC 1.7.3.3)-catalase (EC 1.11.1.6)-formaldehyde dehydrogenase (FADH, EC 1.2.1.46) method coupled with formate dehydrogenase (formate:NAD oxidoreductase, FDH, EC 1.2.1.2). Formate dehydrogenase from Pseudomonas oxalaticus catalyzes the formation of NADH from formate produced by FADH. Owing to the NADH and formate oxidase activity of the FDH itself, the full reaction curve is not linear, but gradually decreases. The formation of NADH is not stoichiometric with formate removal, but is strictly proportional to it. To overcome this decrease of extinction, we added hydroxylamine hydrochloride to the FDH. The sensitivity of the full reaction in the presence of FDH was about 1.8 times that without FDH. Analysis with a Cobas Bio centrifugal analyzer revealed a linearity of up to 3.56 mmol/L. The uricase-catalase-alcohol dehydrogenase method correlated well with the uricase-peroxidase-chromogen method. Our method is more sensitive than other methods.

Aldehyde Oxidoreductases↗

PubMed2003

Oxidative damage to mouse lens in culture. Protective effect of pyruvate.

Studies have been conducted to examine the feasibility of preventing oxyradical-dependent oxidative stress to mouse lens in culture, using pyruvate as an antioxidant. The extent of oxidative damage to the tissue was assessed by measurement of the status of Na(+)-K(+) ATPase dependent active transport of rubidium 86Rb(+). The tissue levels of adenosine triphosphate (ATP), glutathione (GSH), malonaldehyde (MDA) and catalase were also determined. While the measurement of 86Rb(+) uptake provides an assessment of the integrity of the primary active transport system, measurement of the other components reflects the status of intracellular oxidative stress. ATP measurement also reflected on the overall status of metabolic integrity. Incubation of the lens with xanthine (XA)/xanthine oxidase (XO) system had an adverse effect on all these parameters. Incorporation of pyruvate was strikingly protective. The protective effect of pyruvate is apparently due to its ability to scavenge ROS generated in the medium with the possibility of its action on tissue metabolism as well. The findings are hence considered useful for further studies on the prevention of oxidative stress to tissues by exogenous supplementation with pyruvate, specially the human lens where the biochemistry of its antioxidant mechanisms is similar to the mouse lens, contrary to the rat lens.

Adenosine Triphosphate↗

PubMed2000

Interaction of hypoxanthine/xanthine oxidase with nitrergic relaxation in the porcine gastric fundus.

The influence of hypoxanthine (HX)/xanthine oxidase (XO) on short-term [electrical field stimulation (EFS; 4 Hz) for 10 s and 3 min; bolus of exogenous NO (10(-5) M)] and long-term [EFS (4 Hz) and continuous NO-infusion for 20 min] nitrergic relaxations was investigated in circular muscle strips of the pig gastric fundus. HX (3x10(-4) M) / XO (64 mu ml(-1)) did not affect EFS for 10 s and 3 min; the short-lasting relaxation in response to a bolus of exogenous NO (10(-5) M) was changed into a biphasic relaxation with a small and short first phase followed by a larger and prolonged second phase. Cu/Zn superoxide dismutase (Cu/Zn SOD; 1000 u ml(-1)) and uricase (100 mu ml(-1)) respectively enhanced the amplitude of the first phase and diminished the amplitude of the second phase. Ascorbate (5x10(-4) M) and bilirubin (2x10(-4) M) prevented the prolonged component. Exposure to HX/XO during long-term EFS elicited a complete, stable reversal of relaxation starting after a delay. During continuous NO-infusion, HX/XO induced an immediate, complete but transient reversal. The antioxidants bilirubin, ascorbate, alpha-tocopherol, urate, glutathione and Cu/Zn SOD, the hydrogen peroxide degrading enzyme catalase, the hydroxyl radical scavengers dimethylsulphoxide and mannitol, and the cofactor flavin adenine dinucleotide did not influence the reversal induced by HX/XO during either EFS or NO-infusion. The cell-permeable manganese SOD mimetic EUK-8 modified the stable reversal during long-term EFS into a transient one. The results suggest that a nitrated uric acid derivative is responsible for the prolonged second phase in the relaxation to a bolus of exogenous NO in the presence of HX/XO. The exact underlying mechanism of the reversal induced by HX/XO during sustained relaxation remains unclear.

Animals↗