The Experts below are selected from a list of 207 Experts worldwide ranked by ideXlab platform
Lynette B. Keur - One of the best experts on this subject based on the ideXlab platform.
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Role of Xanthine Oxidase in the Reduction of Resazurin by Raw Milk
Journal of Dairy Science, 2010Co-Authors: J. J. R. Campbell, Lynette B. KeurAbstract:The addition to raw milk of a variety of substrates for Xanthine Oxidase resulted in an almost immediate reduction of resazurin. When no substrate was added, doubling the concentration of Xanthine Oxidase in raw milk by the addition of purified enzyme did not cause a significant increase in the rate of resazurin reduction, confirming the conclusion that the unavailability of substrate limits the reducing activity of this enzyme. Milk from two cows which were very low in Xanthine Oxidase did show an increased reduction rate on the addition of the purified enzyme, but the final rate was still much too slow to have any bearing on the commercial grade of the milk. The pasteurization of milk destroyed the ability to reduce resazurin but had little influence on the activity of Xanthine Oxidase. The addition to milk of folic acid, a very effective competitive inhibitor for Xanthine Oxidase, failed to slow the rate of resazurin reduction signiflcantly. All of these factors point to the fact that Xanthine Oxidase does not play a significant role in the reduction of resazurin by raw milk. © 1961, American Dairy Science Association. All rights reserved.
J. J. R. Campbell - One of the best experts on this subject based on the ideXlab platform.
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Role of Xanthine Oxidase in the Reduction of Resazurin by Raw Milk
Journal of Dairy Science, 2010Co-Authors: J. J. R. Campbell, Lynette B. KeurAbstract:The addition to raw milk of a variety of substrates for Xanthine Oxidase resulted in an almost immediate reduction of resazurin. When no substrate was added, doubling the concentration of Xanthine Oxidase in raw milk by the addition of purified enzyme did not cause a significant increase in the rate of resazurin reduction, confirming the conclusion that the unavailability of substrate limits the reducing activity of this enzyme. Milk from two cows which were very low in Xanthine Oxidase did show an increased reduction rate on the addition of the purified enzyme, but the final rate was still much too slow to have any bearing on the commercial grade of the milk. The pasteurization of milk destroyed the ability to reduce resazurin but had little influence on the activity of Xanthine Oxidase. The addition to milk of folic acid, a very effective competitive inhibitor for Xanthine Oxidase, failed to slow the rate of resazurin reduction signiflcantly. All of these factors point to the fact that Xanthine Oxidase does not play a significant role in the reduction of resazurin by raw milk. © 1961, American Dairy Science Association. All rights reserved.
Jay L. Zweier - One of the best experts on this subject based on the ideXlab platform.
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substrate control of free radical generation from Xanthine Oxidase in the postischemic heart
Journal of Biological Chemistry, 1995Co-Authors: Jay L. ZweierAbstract:Abstract While the free radical-generating enzyme Xanthine Oxidase is a central mechanism of injury in postischemic tissues, questions remain regarding how Xanthine Oxidase-mediated radical generation is triggered during ischemia and reperfusion. There is controversy regarding whether radical generation is caused by enzyme formation or that of its substrates Xanthine and hypoXanthine. Therefore, studies were performed in isolated rat hearts correlating the magnitude and time course of radical generation with alterations in Xanthine Oxidase and its substrates. Radical generation was measured by electron paramagnetic resonance spectroscopy and correlated with spectrophotometric assays of tissue Xanthine Oxidase activity and chromatographic measurement of tissue and effluent concentrations of Xanthine Oxidase substrates and products. Xanthine Oxidase was present in preischemic hearts and slightly increased during 30-min global ischemia. HypoXanthine and Xanthine were not present prior to ischemia but accumulated greatly during ischemia due to ATP degradation. These substrate concentrations rapidly declined over the first 5 min of reperfusion matching the observed time course of radical generation, whereas Xanthine Oxidase activity was largely unchanged. Both substrates were also observed in the coronary effluent during the first 5 min of reflow along with the product uric acid. Thus, the burst of Xanthine Oxidase-mediated free radical generation upon reperfusion is triggered and its time course controlled by a large increase in substrate formation that occurs secondary to the degradation of ATP during ischemia.
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Evaluation of the role of Xanthine Oxidase in myocardial reperfusion injury.
Journal of Biological Chemistry, 1990Co-Authors: Susan L. Thompson-gorman, Jay L. ZweierAbstract:Abstract The free radical-generating enzyme Xanthine Oxidase has been hypothesized to be a central mechanism of the injury which occurs in postischemic tissues; however, its importance remains controversial. Much attention has focused on the role of this enzyme in myocardial reperfusion injury. While Xanthine Oxidase has been observed in ischemic tissue homogenates, the presence and importance of radical generation by the enzyme in intact tissues are unknown. Therefore, we performed electron paramagnetic resonance, nuclear magnetic resonance and hemodynamic studies to measure the presence and significance of Xanthine Oxidase-mediated free radical generation in the isolated rat heart. When isolated perfused rat hearts were reperfused after 30 min of global ischemia, myocardial function and coronary flow were significantly improved in the presence of the definitive Xanthine Oxidase blocker oxypurinol. Free radical concentrations measured by spin-trapping with 5,5'-dimethyl-1-pyrroline-N-oxide were significantly decreased by oxypurinol and the energetic state of the heart was improved as reflected by an increased recovery of phosphocreatine and a higher phosphocreatine/Pi ratio. ATP recovery, however, was not altered, indicating that the improved functional and metabolic state of the heart was not due to ATP salvage. Spectrophotometric assays for the enzyme showed an increase in the amount of Xanthine Oxidase relative to dehydrogenase following ischemia, and a total available Xanthine Oxidase pool in the rat heart of approximately 150 milliunits/g of protein. Thus, Xanthine Oxidase is a significant source of the oxidative injury which occurs upon reperfusion of the ischemic rat heart.
Erik A Richter - One of the best experts on this subject based on the ideXlab platform.
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Xanthine Oxidase in human skeletal muscle following eccentric exercise a role in inflammation
The Journal of Physiology, 1997Co-Authors: Ylva Hellsten, U Frandsen, N Orthenblad, B Sjodin, Erik A RichterAbstract:1. The present study tested the hypothesis that the level of Xanthine Oxidase is elevated in injured human skeletal muscle in association with inflammatory events. Seven male subjects performed five bouts of strenuous one-legged eccentric exercise. Muscle biopsies from both the exercised and the control leg, together with venous blood samples, were obtained prior to exercise and at 45 min, 24, 48 and 96 h after exercise. The time courses of Xanthine Oxidase immunoreactivity and indicators of muscle damage and inflammation were examined. 2. The number of Xanthine Oxidase structures observed by immunohistological methods in the exercised muscle was up to eightfold higher than control from day 1 to day 4 after exercise (P < 0.05). The increase was attributed to an enhanced expression of Xanthine Oxidase in microvascular endothelial cells and an invasion of leucocytes containing Xanthine Oxidase. 3. The concentration of plasma interleukin-6 was significantly higher 90 min after exercise than before exercise (P < 0.05) and remained higher than pre-exercise levels throughout the 4 days. On day 4 the plasma creatine kinase activity was approximately 150-fold higher (P < 0.05) than resting levels. 4. Despite the increase in Xanthine Oxidase in the muscle there were no detectable changes in the levels of muscle malondialdehyde or in plasma antioxidant capacity up to 4 days post-exercise. 5. It is concluded that eccentric exercise leads to an increased level of Xanthine Oxidase in human muscle and that the increase is associated with secondary inflammatory processes. The increase in Xanthine Oxidase in the muscle occurs mainly in microvascular endothelial cells, but occurs also via infiltrating leucocytes containing Xanthine Oxidase. A role for leucocytes in Xanthine Oxidase induction in endothelium is proposed.
James G. Lecce - One of the best experts on this subject based on the ideXlab platform.
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Copurification of bovine milk Xanthine Oxidase and immunoglobulin
Archives of Biochemistry and Biophysics, 1991Co-Authors: Debra A Clare, James G. LecceAbstract:Xanthine Oxidase, isolated from bovine milk, exhibited an A280:A450nm ratio of 5.0. This ratio is reported to be indicative of highly purified enzyme preparations. Serum from a rabbit hyperimmunized against this enzyme fraction exhibited two precipitation lines when incubated with the protein in agarose double diffusion plates. Serum albumin, ??-lactoglobulin, ??-lactalbumin, lactoferrin, casein, chymosin, and immunoglobulin were tested for reactivity. The second antigen was identified as bovine immunoglobulin. Commercial preparations of Xanthine Oxidase also contained immunoglobulin as a contaminant. IgG and IgA were present in Sigma (Grade III) fractions and IgM was identified in Boehringer Mannheim preparations. Immunofluorescent studies indicated that Xanthine Oxidase antiserum reacted with the capillary endothelium of bovine heart. Absorption of this antiserum with bovine IgG abrogated this reaction. These findings may explain apparent discrepancies between reported immunohistological association of Xanthine Oxidase in heart capillary endothelial cells and the absence of detectable enzymatic activity. ?? 1991.
