Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.17.3.2 (xanthine oxidase)
8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The present study tested the hypothesis that calpain is responsible for the limited proteolytic conversion of xanthine dehydrogenase (XD) to xanthine oxidase (XO). We compared the effects of various proteases on the activity and molecular weight of a purified preparation of xanthine dehydrogenase from rat liver. In agreement with previous reports, trypsin treatment produced a complete conversion of XD to XO accompanied by a limited proteolysis of XDH from an Mr of 140 kD to an Mr of 90 kD. Treatment with calpain I or calpain II did not produce a conversion from XD to XO nor did it result in partial proteolysis of the enzyme. Similarly, trypsin treatment partially degraded a reversibly oxidized form of xanthine dehydrogenase while calpain I or calpain II were ineffective. The possibility that an endogenous inhibitor prevented the proteolysis of XDH by calpain I or II was excluded by verifying that brain spectrin, a known calpain substrate, was degraded under the same incubation conditions. The results indicate that calpain is not likely to be responsible for the in vivo conversion of XD to XO under pathological conditions.
...
PMID:Proteolytic conversion of xanthine dehydrogenase to xanthine oxidase: evidence against a role for calcium-activated protease (calpain). 255 23

The influence of regulatory peptides (somatostatin, calcitonin, and dalargin) on xanthine oxidase activity and lipid peroxidation level in pancreatic tissues as well as on the release of pancreatic enzymes (alpha-amylase, trypsin, lipase, and transamidinase) into blood was studied in 205 rats with experimental acute pancreatitis. Somatostatin and dalargin were shown to have obvious antioxidant effect seen by reduced xanthine oxidase activity and MDA level. All studied peptides stimulate reduced release of pancreatic enzymes. Particularly, reduction of dalargin and somatostatin is caused by inhibition of their synthesis as well as by pancreas protective effect of the peptides. Release of enzymes reduced by calcitonin is probably associated only with inhibition of secretory activity of the pancreas.
...
PMID:[Effects of several regulatory peptides on the functional activity of the pancreas in acute experimental pancreatitis]. 259 53

Superoxide anion (O2-) generated from xanthine oxidase/xanthine has been used to decrease the half life of endothelium derived relaxing factor (EDRF). However, by itself, xanthine oxidase causes endothelium dependent relaxation. This relaxation is unrelated to the oxidative property of the enzyme since it is not inhibited by allopurinol. In addition, the relaxation is not inhibited by the cyclooxygenase inhibitor, indomethacin, or the phospholipase A2 inhibitor, p-bromophenacyl bromide. On the other hand the relaxation is inhibited by the trypsin inhibitor (TI) from chicken egg white. A similar endothelium dependent relaxation elicited by pancreatin and trypsin is also inhibited by TI. Pancreatin used in the preparation of xanthine oxidase contains trypsin, chymotrypsin and carboxypeptidase. When compared to trypsin both chymotrypsin and carboxypeptidase elicit little relaxation. Thus the endothelium dependent relaxation elicited by xanthine oxidase is likely due to contamination with trypsin. Our results emphasize that when the superoxide generating system, xanthine oxidase/xanthine is used to study the effect of oxygen radicals on EDRF, it is advantageous to ensure that only purified preparations of xanthine oxidase are used.
...
PMID:Xanthine oxidase and endothelium dependent relaxation. 282 Apr 11

Xanthine oxidase (EC 1.2.3.2) was purified from fresh cows' milk by differential centrifugation and hydroxylapatite chromatography in the absence of reducing agents and proteases. The purified isolate possessed an absorbance at 280 nm:absorbance at 450 nm ratio of 4.84; an absorbance (1 cm at 280 nm 1%) of 11.9; an activity:absorbance at 450 nm of 141, a specific activity of 3.59 units/mg; and detectable dehydrogenase activity. The enzyme preparation was obtained in a reversible oxidase form that could be partially converted to xanthine dehydrogenase in the presence of 10mM dithiothreitol or 1% mercaptoethanol. Amino acid analyses revealed that the enzyme was hydrophobic in nature and that lysine constituted its N-terminal residue. The protein contained 22 disulfide and 38 sulfhydryl groups, four of which were detectable in the undenatured protein complex. Discontinuous PAGE in the presence of selected dissociation agents did not result in further resolution. Sodium dodecyl sulfate-PAGE of the purified enzyme revealed a sharp zone with a molecular weight of 151,000 +/- 4000 (i.e., monomer). The purified enzyme exhibited oxidase activity in the presence of 6 M urea and following limited proteolysis by trypsin, chymotrypsin, plasmin, pancreatin, pepsin, and papain. Proteolyzed xanthine oxidase migrated as a single zone in polyacrylamide gels in the presence and absence of dissociating agents such as 1% mercaptoethanol and 6 M urea. Restricted digestion of xanthine oxidase by proteases was indicated by the presence of three major zones with molecular weights ranging from 85,000 to 100,000, 30,000 to 35,000, and 18,000 to 20,000 commonly observed in SDS gels. Amino acid profiles of the principal peptidyl fragments of trypsin-cleaved xanthine oxidase indicated their hydrophobic nature and lysine as the N-terminal residue for all fragments.
...
PMID:Characteristics of purified cows' milk xanthine oxidase and its submolecular characteristics. 339 6

The specific susceptibility of the intestinal mucosa to low blood flow states is related to the "physiologic" makeup of the intestinal milieu. Pancreatic proteases appear to play a crucial role in the ischemic autodigestion of the intestinal mucosa. Moreover, trypsin can activate the conversion of xanthine dehydrogenase into superoxide radicals producing xanthine oxidase. Oxygen-derived free radicals account for at least part of the damage to the postischemic intestinal mucosa.
...
PMID:Pancreatic proteases and oxygen-derived free radicals in acute ischemic enteropathy. 351 Apr 80

Xanthine oxidase employs four electron transport sites (flavin adenine dinucleotide (FAD), molybdenum, and two FeS centers) in catalyzing a variety of redox reactions. To determine whether the redox sites reside in independent domains of the enzyme, the temperature of heat inactivation of each site's catalytic activity was determined, except that no attempt was made to distinguish between the two FeS sites. In the oxidase form of xanthine oxidase, the order of thermal stabilities was Mo greater than FAD greater than FeS, while after conversion to its dehydrogenase form the above ranking was Mo greater than FeS greater than FAD. The small but reproducible difference in heat inactivation temperatures among the redox sites demonstrated that the sites are located in separate domains of the enzyme. To confirm the above segregation of redox centers, the temperature of heat-induced release of each redox cofactor from its site on the enzyme was examined. These temperatures were found to be different for each redox cofactor and agreed closely with the heat inactivation temperatures measured above. The data thus demonstrate that both heat inactivation and cofactor release derive from thermal unfolding of independent domains. Using a technique termed "thermal digestion analysis," the FAD domain was located in a approximately equal to 42,000-Da tryptic fragment, while the FeS and Mo domains were isolated in a trypsin-resistant 92,000-Da fragment. We conclude that xanthine oxidase is constructed in modular fashion with the redox sites located in independent structural domains.
...
PMID:The redox centers of xanthine oxidase are on independent structural domains of the enzyme. 377 44

1. The xanthine oxidase of cow's milk, crude or purified, appears as an oxidase (type O), and can be converted almost completely into a NAD(+)-dependent dehydrogenase (type D) by treatment with dithioerythritol or dihydrolipoic acid, but only to a small extent by other thiols. 2. The D form of the enzyme is inhibited by NADH, which competes with NAD(+). 3. The kinetic constants of the two forms of the enzyme are similar to those of the corresponding forms of rat liver xanthine oxidase. 4. Milk xanthine oxidase is converted into an irreversible O form by pretreatment with chymotrypsin, papain or subtilisin, but only partially with trypsin. 5. The enzyme as purified shows a major faster band and a minor slower band on gel electrophoresis. The slower band is greatly reinforced after xanthine oxidase is converted into the irreversible O form by chymotrypsin.
...
PMID:Milk xanthine oxidase type D (dehydrogenase) and type O (oxidase). Purification, interconversion and some properties. 435 4

1. Two major forms of xanthine oxidase are demonstrated for the mouse. On polyacrylamide-gel electrophoresis the duodenal form migrates faster towards the anode than that of the liver. Both forms also differ in their (NH(4))(2)SO(4) precipitation patterns and sucrose-density-gradient molecular-weight determinations. 2. The liver form is fully converted into the duodenal form by incubation at 37 degrees C with 2.5mg of crude trypsin/ml for 1(1/2)h, without loss of activity. The trypsin-treated liver form behaves like the normal duodenal form as characterized by electrophoresis, (NH(4))(2)SO(4) precipitation patterns, and sucrose-density-gradient molecular-weight determinations. 3. Partial conversion is also brought about by purified trypsin and chymotrypsin, but not with beta-carboxypeptidase or lipase. The conversion is inhibited by soya-bean trypsin inhibitor. 4. In embryo mice the duodenal form is similar to the liver form on electrophoresis. 5. These studies indicate, as might be expected, that the duodenal form is a modified version of the liver enzyme, probably caused by proteolytic alteration.
...
PMID:Characterization of alternative molecular forms of xanthine oxidase in the mouse. 472 35

1. The topography of cytochrome P-450 in vesicles from smooth endoplasmic reticulum of rat liver has been examined. Approx. 50% of the cytochrome is directly accessible to the action of trypsin in intact vesicles whereas the remainder is inaccessible and partitioned between luminal-facing or phospholipid-embedded loci. Analysis by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis reveals three major species of the cytochrome. Of these, the variant with a mol.wt. of 52000 is induced by phenobarbitone and this species is susceptible to trypsin. 2. After trypsin treatment of smooth membrane, some NADPH-cytochrome P-450 (cytochrome c) reductase activity remains and this remaining activity is enhanced by treatment with 0.05% deoxycholate, which renders the membranes permeable to macromolecules. In non-trypsin-treated control membranes the reductase activity is increased to a similar extent. These observations suggest an asymmetric distribution of NADPH-cytochrome P-450 (cytochrome c) reductase in the membrane. 3. As compared with dithionite, NADPH reduces only 44% of the cytochrome P-450 present in intact membranes. After tryptic digestion, none of the remaining cytochrome P-450 is reducible by NADPH. 4. In the presence of both a superoxide-generating system (xanthine plus xanthine oxidase) and NADPH, all the cytochrome P-450 in intact membrane (as judged by dithionite reducibility) is reduced. The cytochrome P-450 remaining after trypsin treatment of smooth vesicles cannot be reduced by this method. 5. The superoxide-dependent reduction of cytochrome P-450 is prevented by treatment of the membranes with mersalyl, which inhibits NADPH-cytochrome P-450 (cytochrome c) reductase. Thus the effect of superoxide may involve NADPH-cytochrome P-450 reductase and cytosolically orientated membrane factor(s).
...
PMID:Asymmetric distribution of cytochrome P-450 and NADPH--cytochrome P-450 (cytochrome c) reductase in vesicles from smooth endoplasmic reticulum of rat liver. 625 76

The oxygen radical generating system of xanthine oxidase plus xanthine, which has been used as a model for the oxidative burst of activated granulocytes, is known to damage endothelium in vivo and in vitro. We previously observed effects (inhibited by catalase, and thus associated with the formation of H2O2) on several parameters of endothelial function, using a non-commercial preparation of xanthine oxidase. Our present study demonstrates that xanthine oxidase from two different commercial sources has additional effects on endothelial morphology and ion flux that are substrate-independent (i.e. produced in the absence of added xanthine) and are attributable to the presence of pancreatin (a crude enzyme mixture used in the commercial preparation of xanthine oxidase from milk). These effects are related to the tryptic activity of pancreatin and extend previous observations on the effects of neutral proteases on endothelial cells. Our results emphasise the practical point that studies on the effects of commercial xanthine oxidase preparations on endothelial cells must take account of their trypsin-like activity as well as their capacity to generate oxygen products.
...
PMID:Stimulation of endothelial cells by protease activity in commercial preparations of xanthine oxidase. 638 77


<< Previous 1 2 3 4 Next >>

---