Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Metabolism of guanine and guanine nucleotides in primary rat neuronal cultures. 131 76

Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193), a selective inhibitor of the activity of IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, provided in end stage leukemic patients a rapid decrease of IMP dehydrogenase activity and GTP concentration in the blast cells and a subsequent decline in blast cell count. Sixteen consecutive patients with end stage acute nonlymphocytic leukemia or myeloid blast crisis of chronic granulocytic leukemia were treated with tiazofurin. Allopurinol was also given to inhibit xanthine oxidase activity to decrease uric acid excretion and to elevate the serum concentration of hypoxanthine, which should competitively inhibit the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), the salvage enzyme of guanylate synthesis. Assays of IMP dehydrogenase activity and GTP concentration in leukemic cells provided a method to monitor the impact of tiazofurin and allopurinol and to adjust the drug doses. In this group of patients with poor prognosis, five attained a complete hematological remission and one showed a hematological improvement. A marked antileukemic effect was seen in two other patients. All five evaluable patients with myeloid blast crisis of chronic granulocytic leukemia reentered the chronic phase of their disease. Five patients with acute nonlymphocytic leukemia were refractory to tiazofurin and three were unevaluable for hematological effect because of early severe complications. Responses with intermittent 5- to 15-day courses of tiazofurin lasted 3-10 months. Tiazofurin had a clear antiproliferative effect, but the pattern of hematological response indicated that it appeared to induce differentiation of leukemic cells. In spite of toxicity with severe or life-threatening complications in 11 of 16 patients, tiazofurin was better tolerated in most patients than other antileukemic treatment modalities and provided a rational, biochemically targeted, and biochemically monitored chemotherapy which should be of interest in the treatment of leukemias and as a paradigm in enzyme pattern-targeted chemotherapy.
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PMID:Biochemically directed therapy of leukemia with tiazofurin, a selective blocker of inosine 5'-phosphate dehydrogenase activity. 256 8

Crude tissue or tumor extracts either do not contain sufficient inosine 5'-monophosphate dehydrogenase (IMPD) activity to be measured spectrophotometrically, or interfering enzyme activities prevent the use of a more sensitive radiochemical assay. A modified assay system which incorporates alpha, beta-methylene adenosine 5'-diphosphate, an inhibitor of 5'-nucleotidase; allopurinol, an inhibitor of xanthine oxidase; and ethylenediaminetetraacetate, an inhibitor of alkaline phosphatase, has been developed. [14C]Xanthine monophosphate produced during the assay was separated from [14C]hypoxanthine monophosphate by thin-layer chromatography on flexible diethylaminoethyl-cellulose sheets. Xanthine monophosphate formation was linear for at least 40 min and was inhibited by greater than 95% in the presence of mycophenolic acid, a specific IMPD inhibitor. Partial purified IMPD from murine EMT6 tumors was used to compare assay rates obtained with the radiochemical and spectrophotometric assays under identical conditions. The reaction rate of the radiochemical assay was 0.92 +/- 0.07 (S.E.) of the rate of xanthine monophosphate formation as determined spectrophotometrically at 290 nm, indicating that both assays are measuring product formation with an equal degree of accuracy. The improved radiochemical assay was used to determine IMPD specific activity in supernatants from EMT6 tumors and several normal mouse tissues. The observed activities (nmol/min/mg protein) were: EMT6 tumor, 0.303; spleen, 0.029; brain, 0.022; kidney, 0.015; lung, 0.009; liver, 0.008; and heart and skeletal muscle, less than 0.004.
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PMID:Sensitive radiochemical assay for inosine 5'-monophosphate dehydrogenase and determination of activity in murine tumor and tissue extracts. 613 40

Inhibition of conversion from IMP to uric acid, which interferes with both spectrophotometric and radioisotopic assays of IMP dehydrogenase, by addition of allopurinol (0.1 mM), an inhibitor of xanthine oxidase, to the incubation system made it possible to determine the enzyme activity in crude liver extracts. With this improved assay method, the regulatory properties of the enzyme in crude extracts of liver and Yoshida sarcoma ascites cells were examined. In both tissues IMP dehydrogenase was found in the postmicrosomal supernatant. However, further centrifugation resulted in precipitation of the enzyme, the enzyme from Yoshida sarcoma ascites cells being precipitated more easily than that from rat liver. It was also found that IMP dehydrogenase activity increased during liver regeneration and that this increase was associated with the precipitate from the postmicrosomal fraction. These findings suggest that such a large sedimentable complex including IMP dehydrogenase might be formed in relation to cell growth. Most of the enzyme activity in rat liver and Yoshida sarcoma ascites cells was extracted in the supernatant obtained by centrifugation at 105,000 X g for 4 h after treatment of tissue homogenates with 1 M KCl, 0.75 M (NH4)2SO4, 2 M dimethylsulfoxide, 2 M KSCN, 25% glycerol, or 0.8 M guanidine-HCl. Treatment with 2% deoxycholate, 2% Triton X-100 or 2 M urea gave limited extraction. The enzyme was retained on a phenyl-Sepharose CL-6B or octyl-Sepharose CL-6B column and eluted with 0.8 M guanidine-HCl. These results suggested that the enzyme molecule has not only ionic but also hydrophobic domains, through which it interacts with other molecules of the enzyme itself and/or postmicrosomal cellular components.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:IMP dehydrogenase. I. Studies on regulatory properties of crude tissue extracts based on an improved assay method. 614 Feb 63

The rate of purine de novo synthesis from sodium formate in developing rat brain falls in the late gestational stages to birth, rises again in the 1st week of life and then decreases rapidly to the 3rd week, and continues declining up to 8 weeks of life (adulthood). The changes in the overall purine biosynthetic rate with respect to time are similar to those in the activity of the rate-limiting enzyme [amidophosphoribosyltransferase (phosphoribosyl diphosphate amidotransferase; EC 2.4.2.14)]. Azaserine [O-diazoacetyl-L-serine], a known inhibitor of glutamine requiring metabolic steps, inhibits purine de novo synthesis by more than 90%. This confirms that the method used to assess purine de novo synthesis in fact does so. The effects of virazole [1-beta-ribofuranosyl-1-H,1,2,4-triazole-3-carboxamide], an inhibitor of IMP dehydrogenase (EC 1.2.1.14), and of alanosine [L-2-amino-3-(hydroxynitrosamino)propanoic acid] an inhibitor of adenylosuccinate synthetase (EC 6.3.4.4), on the rate of purine de novo synthesis were investigated in liver and brain tissue. The effect of the xanthine oxidase inhibitor allopurinol [4-hydroxypyrazolo(3,4-d)pyrimidine] was also investigated in liver tissue. The biosynthesis of the purines which were extruded into the incubation medium as well as those which remained in the tissue was studied. Only inhibitory effects were observed, and these were confined to the purines remaining in the tissue. Allopurinol was completely inert from this viewpoint. The results are compared with those of other workers using lymphoid cells, and emphasize the differences in the control of de novo purine synthesis in different tissues and under different conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Purine de novo synthesis in liver and developing rat brain, and the effect of some inhibitors of purine nucleotide interconversion. 662 51

In cancer cells, a marked imbalance in the enzymic pattern of purine metabolism is linked with transformation and/or progression. In chemically-induced, transplantable hepatomas in rat, the specific activities of the anabolic enzymes, IMP dehydrogenase, GMP synthetase, adenylosuccinate synthetase, adenylosuccinase, AMP deaminase and amidophosphoribosyltransferase, increased to 13.5-, 3.7-, 3.1-, 1.8-, 5.5- and 2.8-fold, respectively, of those in normal liver. Activities of the catabolic enzymes, inosine phosphorylase, xanthine oxidase and uricase, decreased to 19, 10 and 4%, respectively. This enzymic imbalance was specific to hepatic neoplasia, since no similar pattern was observed in differentiating or regenerating liver. Most enzymic alterations were present also in chemically- and virus-induced animal tumors, in human kidney, liver and colon carcinomas, and in human colon carcinoma xenografts. The molecular correlation concept applies to purine biochemistry and an important segment of neoplastic gene expression was identified in the behavior of key purine-metabolizing enzymes.
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PMID:Enzymes of purine metabolism in cancer. 686 38

Metabolism of thiopurine drugs--azathioprine, 6-mercaptopurine, and 6-thioguanine--has provided a powerful pharmacogenetic model incorporating polymorphism of the enzyme thiopurine methyltransferase (TPMT) and the primary active metabolite, thioguanine nucleotide (TGN). However, a sense of uncertainty about the usefulness of TGNs and other thiopurine metabolites has appeared. This review critically appraises the basis of thiopurine metabolism and reveals the problems and complexities in TGN research. Erythrocyte TGN is used in transplantation medicine and in chronic inflammatory conditions such as Crohn's disease, as a "surrogate" pharmacokinetic parameter for TGN in the target cells: leukocytes or bone marrow. It is not generally appreciated that erythrocytes do not express the enzyme IMP dehydrogenase and cannot convert mercaptopurine to TGN, which explains some of the confusion in interpretation of erythrocyte TGN measurements. TGN routinely measured in erythrocytes derives from hepatic metabolism. Another concern is that TGN are not generally assayed directly: most methods assay the thiopurine bases. Ion-exchange HPLC and enzymatic conversion of TGNs to nucleosides have been used to overcome this, and may reveal undisclosed roles for an unusual cytotoxic nucleotide, thio-inosine triphosphate, and methylated thiopurines. There appear to be additional interactions between xanthine oxidase and TPMT, and folate and TPMT, that could predict leukopenia. Difficult questions remain to be answered, which may be assisted by technological advances. Prospective TGN studies, long overdue, are at last revealing clearer results.
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PMID:Thiopurine therapies: problems, complexities, and progress with monitoring thioguanine nucleotides. 1617 40

Thiopurines are widely used in the treatment of inflammatory bowel disease (IBD). However, in clinical practice azathioprine (AZA) or 6-mercaptopurine (6-MP) are not effective in one-third of patients and up to one-fifth of patients discontinue thiopurine therapy due to adverse reactions. The observed interindividual differences in therapeutic response and toxicity to thiopurines are explained to a large extent by the variable formation of active metabolites, which is at least partly caused by genetic polymorphisms of the genes encoding crucial enzymes in thiopurine metabolism. In this in-depth review we discuss the genetic polymorphisms of genes encoding for glutathione S-tranferases, xanthine oxidase, thiopurine S-methyltransferase, inosine triphosphate pyrophosphatase, hypoxanthine phosphoribosyltransferase, inosine monophosphate dehydrogenase and multidrug resistance proteins. Pharmacogenetic knowledge in this field has increased dramatically and is still rapidly increasing, but the translation into practical guidelines with tailored advices will cost much effort in the near future.
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PMID:Pharmacogenetics of thiopurines in inflammatory bowel disease. 2020 60