Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.17.3.2 (xanthine oxidase)
 8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Xanthine dehydrogenase/xanthine oxidase (XDH/XO) is a major cytoplasmic source of superoxide radicals and hydrogen peroxide, and it is considered important in the pathogenesis of ischemia-reperfusion damage. Because little is known about the enzyme in human tissues, the aims of this study were to purify human XDH/XO and to produce Ab for detection of the protein in Western blots and for quantification by ELISA. We purified human milk XDH/XO, produced Ab for Western blotting and ELISA of the protein, and evaluated the molecular forms and activity-protein relationships in human tissues. The molecular size of the purified protein under nondenaturing conditions was approximately 300 kd. On SDS-PAGE, it was fragmented into four main bands of 143, 125, 87, and 59 kd. Ab recognized bands of similar size in Western blots of the purified preparation and human milk. In fresh liver homogenates treated with anti-proteases, the three largest bands were observed; in the intestine, only the two largest were observed. Serum, brain, heart, and skeletal muscle were negative, whereas some lung and kidney samples showed one faint band of 143 kd. Trypsin treatment of the enzyme converted the large molecular-weight bands into smaller bands, as did incubation of a liver homogenate without anti-proteases. XDH/XO protein concentrations (ng/mg total protein) were 146 +/- 70 in liver and 556 +/- 320 in intestine and less than 5 ng/ml in serum. The relationship of activity to protein (2.7-3.0 mumol/min/mg XDH/XO protein) was constant in liver and intestine during development. We conclude that 1) human XDH/XO has molecular size and subunit structure similar to other mammalian enzymes; 2) the polypeptide chain is unstable, also in the intact cell, despite retained activity; and 3) the amount of inactive XDH/XO in human liver and intestine is apparently small.
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PMID:Organ distribution and molecular forms of human xanthine dehydrogenase/xanthine oxidase protein. 856 97

This study compares the susceptibility of pancreatic acinar cells and zymogen granules against oxidative injury and analyzes the mechanisms involved. Zymogen granules and acinar cells, isolated from rat pancreas, were exposed to a reaction mixture containing xanthine oxidase, hypoxanthine, and chelated iron. Cell function and viability were assessed by various techniques. Trypsin activation was quantified by an Elisa for trypsinogen activating peptide. Integrity of granules was determined by release of amylase. The reaction mixture rapidly generated radicals as assessed by deoxyribose and luminol assays. This oxidative stress caused lysis of granules in a matter of minutes but significant cell death only after some hours. Nevertheless, radicals initiated intracellular vacuolization, morphological damage to zymogen granules and mitochondria, increase in trypsinogen activating peptide, and decrease in ATP already after 5-30 min. Supramaximal caerulein concentrations also caused rapid trypsin activation. Addition of cells but not of granules reduced deoxyribose oxidation, suggesting that intact cells act as scavengers. Caerulein pretreatment only slightly increased the susceptibility of cells but markedly that of granules. In conclusion, isolated zymogen granules are markedly more susceptible to oxidative injury than intact acinar cells, in particular, in early stages of caerulein pancreatitis. The results show that oxidative stress causes a rapid trypsin activation that may contribute to cell damage by triggering autodigestion. Zymogen granules and mitochondria appear to be important targets of oxidative damage inside acinar cells. The series of intracellular events initiated by oxidative stress was similar to changes seen in early stages of pancreatitis.
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PMID:Oxidative injury to isolated rat pancreatic acinar cells vs. isolated zymogen granules. 874 74

The enzyme activities of trypsin (using an artificial substrate, Nalpha-benzoyl-L-arginine-ethylester = BAEE), xanthine oxidase (XOD) and superoxide dismutase (SOD) were measured in the absence and presence of various concentrations of the following inert, water-soluble polymer viscogens: polyvinylpyrrolidone (PVP-40), polyethyleneglycol (PEG-6000) and bovine serum albumin (BSA). Enzyme activities measured in the absence of viscogens were taken as 100%. In the presence of the viscogens, enzyme activities decreased considerably as follows: (i) Trypsin: to 2 or 12% in reaction mixtures containing 64 mg/ml PVP-40 or 481 mg/ml PEG-6000, respectively. (ii) XOD: to 29.3% in a reaction mixture containing 116 mg/ml PVP-40, to 68.9% in a medium containing 266 mg/ml PEG-6000, and 38.1% in the presence of 138 mg/ml BSA. (iii) SOD: to 40.0, 19.9 and 16.6% in the same media as listed for XOD, respectively. The observations are consistent with the predictions of the molecular enzyme kinetic model (MEKM), and are also of importance for the membrane hypothesis of aging, since the latter explains the loss of cell functions by an age-dependent increase of intracellular density which may cause serious enzyme inhibitions.
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PMID:An in vitro model of aging: the influence of increasing physical density on enzyme activities of trypsin, xanthine oxidase and superoxide dismutase. 1537 37