Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.4.4 (adenosine deaminase)
 5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Purine bases and purine nucleosides pass the cell membrane by facilitated diffusion. For purine bases two different carrier proteins seem to exist. Purine bases are trapped intracellularly immediately after passage of the cell membrane by the action of purine phosphoribosyltransferases (PRTs). Comparison of kinetic data of transport and intracellular enzyme reactions shows that intracellular metabolism is rate limiting for the whole uptake process. Since phosphate stimulates the uptake of bases, limited availability of phosphoribosylpyrophosphate (PRPP) might play a regulatory role. Purine nucleosides apparently enter cells via a common carrier. Of the nucleosides under investigation, only adenosine was taken up in significant amounts. Uptake of adenosine is mainly determined by the ratio of adenosine deaminase (ADA) and adenosine kinase (AK) activities. For uptake of purine nucleotides sequential action of ecto-5'-nucleotidase (ecto-5'-NT), nucleoside carrier and intracellular metabolism is necessary. Cells without ecto-5'-NT activity did not accumulate radioactivity from nucleotides. Proliferating neoplastic cells (K 562 and HL 60 cells) showed enhanced uptake of purine bases and nucleosides, when compared to quiescent cells (erythrocytes and granulocytes). From initial rates of uptake and intracellular enzyme activities it could be concluded that this enhanced uptake was due to alterations of enzyme pattern in the neoplastic cells.
 ...
PMID:Regulation of purine uptake in normal and neoplastic cells. 610 May 84

The concept of limiting irreversible damage due to ischemic arrest by inhibiting nucleoside breakdown was tested in the isolated perfused rat heart. Functional recovery measurements were combined with continuous high-energy phosphate measurements by means of 31P nuclear magnetic resonance (NMR) and with nucleoside release measurements in the reperfusion period. The adenosine deaminase inhibitors erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) and 2'-deoxycoformycin (DCF) were given 5 min before ischemia and for the first 5 min of reperfusion. These treated groups were compared with a control, untreated group. These were further compared with a group of hearts arrested with potassium and to a group combining potassium arrest and EHNA. It was found that all treated groups recovered mechanical function significantly better than the untreated group. DCF, K+, and K+ + EHNA slowed ATP decline and resulted in better ATP recovery than untreated or EHNA-treated, and all treatments decreased nucleoside base release. Intracellular pH fell equally in all groups and recovered to preischemic values. Thus, these adenosine deaminase inhibitors improve functional recovery following ischemia, although this improvement was not well correlated with purine losses observed during reperfusion.
 ...
PMID:Effect of adenosine deaminase inhibitors on the heart's functional and biochemical recovery from ischemia: a study utilizing the isolated rat heart adapted to 31P nuclear magnetic resonance. 619 52

AMP-degrading pathways in Azotobacter vinelandii cells were investigated. AMP nucleosidase (EC 3.2.2.4) was rapidly synthesized and reached a maximum at 24 h, while the activity of 5'-nucleotidase (EC 3.1.3.5) specific for AMP, which was negligible during the logarithmic phase of the growth, first appeared in 24 h-cultures, and reached a maximum after complete exhaustion of sucrose from the growth medium (70 h). Cell-free extracts of A. vinelandii of 48 h-cultures hydrolyzed AMP to ribose 5-phosphate and adenine in the presence of ATP, and adenine was deaminated to hypoxanthine. When ATP was excluded, AMP was dephosphorylated to adenosine, which was further metabolized to inosine, and finally to hypoxanthine. Hypoxanthine thus formed was reutilized for the salvage synthesis of IMP under the conditions where 5-phosphoribosyl 1-pyrophosphate was able to be supplied. These results suggest that the levels of ATP can determine the rate of AMP degradation by the AMP nucleosidase- and 5-'nucleotidase-pathways. The role of ATP in the AMP degradation was discussed in relation to the regulatory properties of AMP nucleosidase, inosine nucleosidase (EC. 3.2.2.2) and adenosine deaminase (EC 3.5.4.4).
 ...
PMID:Adenine nucleotide metabolism in Azotobacter vinelandii. Two metabolic pathways of AMP degradation. 626 50

The effects of S-adenosylhomocysteine and S-adenosylmethionine on some purine- and pyrimidine-metabolizing systems have been examined. Both compounds were capable of acting as relatively good inhibitors of adenosine deaminase, nucleoside phosphorylase, and adenylate deaminase activities but as relatively poor inhibitors of myokinase and nucleoside monophosphate kinase. The inhibitory effects were freely reversible. 5'-Nucleotidase, orotidine 5'- phosphate, and phosphodiesterase were unaffected. Nucleoside phosphorylase was competitively inhibited by both compounds, whereas mixed inhibitory effects occurred with adenosine deaminase.
 ...
PMID:The effects of S-adenosylhomocysteine and S-adenosylmethionine on some purine- and pyrimidine-metabolizing systems. 629 1

2'-Deoxycoformycin (DCF) is a potent inhibitor of adenosine deaminase (ADA) and a potential antineoplastic and immunosuppressive agent. In this study the kinetics of ADA expression was assessed by immunomorphologic and enzymatic methods in tissues of ACI rats given injections of DCF. The rats received a daily ip injection of 10 mg DCF/kg for 3 consecutive days. This treatment destroyed cortical thymocytes, whereas lymphocytes of the thymic medulla were mainly preserved. In control phosphate-buffered saline-injected rats, cortical thymocytes were not affected morphologically and displayed strong ADA staining. It was found unexpectedly that injections of DCF produced activation and, possibly, differentiation of B-cells in the mesenteric lymph nodes and spleen. These activated B-lymphocytes and plasma cells stained strongly for ADA. Transient changes in patterns of ADA expression were also observed in endothelial cells of blood vessels and liver Kupffer's cells, but these changes were not accompanied by degeneration of the cells. The treatment with DCF did not result in any permanent abnormalities in the rat tissues.
 ...
PMID:Morphologic changes and immunohistochemical localization of adenosine deaminase in tissues of rats given injections of 2'-deoxycoformycin. 635 8

We have investigated the specificity of the tRNA modifying enzyme that transforms the adenosine at position 34 (wobble position) into inosine in the anticodon of several tRNAs. For this purpose, we have constructed sixteen recombinants of yeast tRNAAsp harboring an AXY anticodon (where X or Y was one of the four nucleotides A, G, C or U). This was done by enzymatic manipulations in vitro of the yeast tRNAAsp, involving specific hydrolysis with S1-nuclease and RNAase A, phosphorylation with T4-polynucleotide kinase and ligation with T4-RNA ligase: it allowed us to replace the normal anticodon GUC by trinucleotides AXY and to introduce simultaneously a 32P-labelled phosphate group between the uridine at position 33 and the newly inserted adenosine at position 34. Each of these 32P-labelled AXY "anticodon-substituted" yeast tRNAAsp were microinjected into the cytoplasm of Xenopus laevis oocytes and assayed for their capacity to act as substrates for the A34 to I34 transforming enzyme. Our results indicate that: 1/ A34 in yeast tRNAAsp harboring the arginine anticodon ACG or an AXY anticodon with a purine at position 35 but with A, G or C but not U at position 36 were efficiently modified into I34; 2/ all yeast tRNAAsp harboring an AXY anticodon with a pyrimidine at position 35 (except ACG) or uridine at position 36 were not modified at all. This demonstrates a strong dependence on the anticodon sequence for the A34 to I34 transformation in yeast tRNAAsp by the putative cytoplasmic adenosine deaminase of Xenopus laevis oocytes.
 ...
PMID:Enzymatic conversion of adenosine to inosine in the wobble position of yeast tRNAAsp: the dependence on the anticodon sequence. 636 51

A method has been developed to measure deoxyribose 1-phosphate in the presence of ribose 1-phosphate and other sugar phosphates. The specificity of the method is based on the observation that only deoxyribose 1-phosphate is hydrolyzed by heating at pH 7.4, while both deoxyribose 1-phosphate and ribose 1-phosphate remain unchanged when heated at pH 10. A tissue extract is heated at pH 10. The amount of deoxyribose 1-phosphate plus ribose 1-phosphate is determined from that of deoxyinosine plus inosine formed in a coupled enzymatic reaction, based on the following two-stage transformation: deoxyribose 1-phosphate (ribose 1-phosphate) + adenine in equilibrium deoxyadenosine (adenosine) + inorganic phosphate, catalyzed by adenosine phosphorylase; deoxyadenosine (adenosine) + H2O----deoxyinosine (inosine), catalyzed by adenosine deaminase. By taking advantage of its unique heat lability, deoxyribose 1-phosphate is eliminated by heating the tissue extract at pH 7.4, and ribose 1-phosphate is determined as above. The amount of deoxyribose 1-phosphate stems from the difference between the amount of deoxyinosine plus inosine measured in the tissue extract heated at pH 10 and that of inosine measured in the tissue extract heated at pH 7.4. Free deoxyribose 1-phosphate has been found in rat tissues, as well as in Bacillus cereus during stationary phase of growth.
 ...
PMID:Deoxyribose 1-phosphate: radioenzymatic and spectrophotometric assays. 643 59

A method for analysis of plasma adenosine which combines the principles of radioisotope dilution and enzymatic catalysis is presented. Plasma from venous heparinized blood containing the adenosine deaminase inhibitor 2'-deoxycoformycin is mixed with a small amount of [3H]adenosine and extracted with perchloric acid. Using highly purified enzyme and [gamma-32P]GTP as the phosphate donor, the neutralized extract then serves as substrate for adenosine kinase, and the AMP product is purified by high-performance liquid chromatography. Adenosine concentrations in plasma are linearly proportional to 32P/3H ratios in the enzymatically synthesized AMP and are calculated from a standard curve. The advantages of the method are: ease of sample preparation; sensitivity of 20 nM in as little as 0.3 ml plasma; 20 samples per day can be analyzed by a single operator. Care must be used when obtaining plasma since cellular contamination will affect results. Using this assay, human plasma adenosine levels are 0.121 +/- 0.054 microM for males and 0.101 +/- 0.067 microM for females.
 ...
PMID:A radioenzymatic assay for plasma adenosine. 652 86

The present work describes an assay which is highly specific for ribose-5-phosphate. The method is based on the following three-stage enzymatic conversion: (1) ribose 5-phosphate in equilibrium ribose 1-phosphate (phosphopentomutase); (2) ribose 1-phosphate + adenine in equilibrium adenosine + Pi (adenosine phosphorylase); (3) adenosine + H2O----inosine + NH3 (adenosine deaminase). Ribose 5-phosphate may be determined either directly following the change in absorbance at 265 nm associated with the conversion of adenine to inosine, or radioenzymatically by measuring the radioactivity of inosine formed from [8-14C]adenine, after chromatographic separation of the nucleoside on polyethyleneimine-cellulose. The spectrophotometric assay was used to follow ribose 5-phosphate formation and ribose 1-phosphate consumption catalyzed by phosphopentomutase. Further, the ability of alkaline phosphatase, 5'-nucleotidase and crude extract of Bacillus cereus cells to act on ribose 5-phosphate was tested. The radioenzymatic assay was proved useful in determining the levels of ribose 5-phosphate in rat tissues.
 ...
PMID:Spectrophotometric and radioenzymatic determination of ribose-5-phosphate. 653 May 7

An analytical method for determination of 2'-deoxycoformycin (2'-DCF) concentrations in plasma and urine was developed based upon a modification of adenosine deaminase (ADA) inhibition assays described in the literature. The method involves the spectrophotometric monitoring of the rate of deamination of adenosine by the enzyme in the presence of various concentrations of the inhibitor 2'-DCF, and relating the deamination rate to the 2'-DCF concentration. In the course of developing the method, it was found that adenosine deaminase appears to lose activity after dilution with phosphate buffer (pH 7.2). Enzyme inactivation was found to occur mono-exponentially with time and, in order to accommodate for this inactivation, a method was developed for quantitating 2'-DCF which takes into consideration the relative activity of the enzyme in the incubation mixtures. The results obtained from the analysis of samples containing known concentrations of 2'-DCF were fitted to a three-dimensional standard surface by means of a nonlinear least-squares regression computer program. Quantitation of 2'-DCF in patient samples is accomplished by an ADA inhibition titration technique in which the spectrophotometrically determined absorbance change is related to the two independent variables, the concentration of 2'-DCF in the standards and the relative time of the analysis. As little as 1 ng/ml of 2'-DCF in plasma can be quantitated with the assay.
 ...
PMID:An enzymatic kinetic method for the determination of 2'-deoxycoformycin in biological fluids. 661 Apr 19


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>