Xanthine Oxidase Activity Levels Research Articles

Xanthine oxidase and dehydrogenase activities in rat ovarian tissues

The production of reactive oxygen species in the ovary is rapidly inducible, but the nature of the generator is unknown. One possibility is xanthine oxidase (XO), an enzyme that produces superoxide in the presence of hypoxanthine (or xanthine) and oxygen. The objective of the present studies was to measure levels of XO in follicular and luteal tissue to determine whether XO may be a source of reactive oxygen species in the rat ovary. Ovarian levels of XO were about one-fifth of that seen in the liver and adrenal, and XO levels were about one-third of xanthine dehydrogenase (XDH). Preovulatory ovarian levels of XO activity were unchanged after induction of ovulation with gonadotropin and in follicles incubated with gonadotropin. Luteal XO activity was not changed during natural or prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis. Allopurinol, an inhibitor of XO, did not inhibit ovulation or PGF2 alpha-induced luteal regression. Finally, neither catalase and superoxide dismutase nor oxypurinol altered luteal cell function in the presence of hypoxanthine. Thus, while XO is present in the ovary, it does not appear that it is a major source of reactive oxygen species in this organ.

Role of oxygen radicals in tourniquet-related ischemia-reperfusion injury of human patients

In the current study we evaluated effluent blood from extremities of human patients undergoing reconstructive surgical treatment which is routinely accompanied by upper extremity exsanguination and application of a tourniquet. Following tourniquet release (reperfusion), there were immediate increases in the plasma levels of xanthine oxidase activity, uric acid, and histamine. Xanthine dehydrogenase activity was not detectable. Plasma also contained products consistent with the formation of oxygen-derived free radicals, namely hemoglobin and fluorescent compounds. Our data indicate in humans that ischemia-reperfusion events are associated with the appearance of xanthine oxidase activity and its products in the plasma effluent.

Bacterial xanthine oxidase from Arthrobacter S-2.

Arthrobacter S-2, originally isolated by enrichment on xanthine, produced high levels of xanthine oxidase activity, requiring as little as a 20-fold purification to approach homogeneity with some preparations. Molecular oxygen, ferricyanide, and 2,6-dichlorophenol-indophenol served as electron acceptors, but nicotinamide adenine dinucleotide did not. The enzyme was relatively specific when compared with previously studied xanthine-oxidizing enzymes, but at least one purine was observed to be oxidized at each of the three positions of the purine ring that have been subject to oxidation by this type of enzyme. The enzyme had a relatively high Km for xanthine (1.3 X 10(-4) M), and substrate inhibition was not observed with this compound, in contrast to the enzyme from cow's milk. In fact, an opposite effect was observed, and double-reciprocal plots with xanthine as the variable substrate showed a concave downward deviation at high concentrations. At 2.5 mM xanthine the enzyme had a specific activity approximately 50 times that of the most active preparations of the milk enzyme. The spectrum of the Arthrobacter enzyme resembled that of milk xanthine oxidase, suggesting a similarity of the prosthetic centers of the two enzymes. The bacterial enzyme was relatively small and may be dimeric, with approximate native and subunit molecular weights of 146,000 and 79,000, respectively.

Participation of Xanthine Oxidase in the Activation of Liver Tryptophan Pyrrolase

Abstract Xanthine oxidase appears to be the endogenous activating agent of inactive holotryptophan pyrrolase. Injection of 4-hydroxypyrazolo[3,4-d]pyrimidine (allopurinol), a competitive inhibitor of xanthine oxidase, in control, hydrocortisone-treated, or tryptophan-treated rats is followed by inhibition of the activity of tryptophan pyrrolase in whole liver homogenates and high speed supernatants. This inhibition is not caused by a direct effect on tryptophan pyrrolase, because allopurinol does not inhibit the activity or conjugation with its prosthetic group in purified preparations of tryptophan pyrrolase. Nor is the synthesis de novo of tryptophan pyrrolase caused by hydrocortisone impaired by allopurinol. Furthermore, removal of xanthine oxidase from high speed liver supernatants by addition of homologous antibody is followed by a loss of activation of the inactive holotryptophan pyrrolase by purines. The degree of activation of the inactive enzyme by purines is dependent upon the level of xanthine oxidase activity. Because this activation by purines is not dependent upon addition of hemoglobin, the xanthine oxidase is apparently activating the inactive holoenzyme.

Role of Xanthine Oxidase in the Development of Spontaneously Oxidized Flavor in Milk

Summary The role of xanthine oxidase in the development of spontaneously oxidized flavor was considered. The study included: (1) the relationship of xanthine oxidase activity to the development of off-flavor, (2) a multiple-enzyme system versus a single enzyme in the development of the off-flavor, and (3) the effect of inhibitors upon the development of spontaneously oxidized flavor. Results of the study indicated that: (1) The occurrence of a spontaneously oxidized flavor in milk was dependent upon a high level of xanthine oxidase activity, (2) a single enzyme (xanthine oxidase) was involved, and (3) inhibitors of xanthine oxidase were effective in preventing flavor development. A brief discussion of the peroxidatic action of xanthine oxidase was included.

栄養素組成と体蛋白質の代謝

Relation between the amounts of dietary protein and enzyme activity was examined by using arbino rats. Casein fed as the source of proiein at levels of 0, 15, 30, 40, 60 and 80 per cent in the diet for eighteen days. Liver xanthine oxidase which is considered to be relate with the metabolism of nuclepprotein was chosen for the enzyme of this experiment. The enzyme activity was measured by a modification of manometric method of AXELROD-ELVEHJEM and colorimetric `method of LITWACK et al. A corelation has been found between these methods. The results showed that the enzyme respons was very sensitive to changes in the content of protein in diets and depleted to “zero” levels at the protein free ration (Table 2). From the values of enzyme activity which was plotted aganist the level of dietary protein (casein) fed, we found that xanthine oxidase activity was increased according to the amount of protein, but no change took place in greater amount than about 30 per cent protein in diet (Fig. 2). The authors suggested that feeding of dietary protein which maintained the stationary level of xanthine oxidase activity was required.