Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Coformycin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed1983

Inhibition of lymphocyte function by 9-deazaadenosine.

9-Deazaadenosine (c9Ado), a novel C-nucleoside, has been found to inhibit lymphocyte-mediated cytolysis (LMC) in a time-dependent manner. c9Ado inhibited LMC by 50% at concentrations of 10 and 0.07 microM after drug-pretreatment periods of 3 and 22 hr, respectively, although a 1-hr pretreatment of cytolytic lymphocytes with 100 microM c9Ado had no effect upon this lymphocyte function. c9Ado was metabolized rapidly and extensively to 9-deazaadenosine 5'-triphosphate (c9ATP) both by mouse cytolytic lymphocytes and by human erythrocytes. Adenosine kinase purified from rabbit liver phosphorylated c9Ado with a Km of 200 microM and a Vmax of 8% that for adenosine. The metabolic buildup of c9ATP in lymphocytes was accompanied by a large, time-dependent decrease in cellular ATP and by smaller percentage decreases in CTP, UTP and GTP. Among other biochemical effects examined, c9Ado was found to cause a decrease in lymphocyte cAMP content and appeared to be neither an inhibitor nor a substrate for S-adenosylhomocysteine hydrolase. Consistent with this latter result, L-homocysteine thiolactone had no effect on the inhibition of LMC by c9Ado. Neither the inhibition of LMC by c9Ado nor the metabolic formation of c9ATP in lymphocytes was affected by erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), indicating that c9Ado is not a substrate for adenosine deaminase. 5-Iodotubercidin, a non-competitive inhibitor (Kis = 9 nM, Ku = 20 nM) of adenosine kinase, prevented the above effects of c9Ado on lymphocyte function, c9ATP formation, and ATP levels. Either complete preservation (with coformycin) or partial replenishment (with adenosine plus EHNA) of ATP levels in c9Ado-treated lymphocytes resulted in partial restoration of cytolytic function to cells containing large amounts of c9ATP. These results suggest that c9Ado is inhibitory to LMC both because it causes a decrease in the absolute concentration of ATP within the cytolytic lymphocytes and because it permits the establishment within these cells of an unfavorable c9ATP:ATP ratio which impedes the utilization of ATP in a reaction essential to the execution of this lymphocyte function.

Adenosine Triphosphate↗
PubMed1988

Alterations in nucleotide pools induced by 3-deazaadenosine and related compounds. Role of adenylate deaminase.

3-Deazaadenine, 3-deazaadenosine, and the carbocyclic analog of 3-deazaadenosine produced similar effects on nucleotide pools of L1210 cells in culture: each caused an increase in IMP and a decrease in adenine nucleotides and had no effect on nucleotides of uracil and cytosine. Concentrations of 50-100 microM were required to produce these effects. Although 3-deazaadenosine and carbocyclic 3-deazaadenosine are known to be potent inhibitors of adenosylhomocysteine hydrolase, the effects on nucleotide pools apparently are not mediated via this inhibition because they are also produced by the base, 3-deazaadenine, and because the concentrations required are higher than those required to inhibit the hydrolase. Cells grown in the presence of 3-deazaadenine or 3-deazaadenosine contained phosphates of 3-deazaadenosine (the mono- and triphosphates were isolated); from cells grown in the presence of the carbocyclic analog of 3-deazaadenosine, the monophosphate was isolated, but evidence for the presence of the triphosphate was not obtained. A cell-free supernatant fraction from L1210 cells supplemented with ATP catalyzed the formation of monophosphates from 3-deazaadenosine or carbocyclic 3-deazaadenosine, and a cell-free supernatant fraction supplemented with 5-phosphoribosyl 1-pyrophosphate (PRPP) catalyzed the formation of 3-deaza-AMP from 3-deazaadenine. Adenosine kinase apparently was not solely responsible for the phosphorylation of the nucleosides because a cell line that lacked this enzyme converted 3-deazaadenosine to phosphates. No evidence was obtained that the effects on nucleotide pools resulted from a block of the IMP-AMP conversion, but the results could be rationalized as a consequence of increased AMP deaminase activity. This explanation is supported by two observations: (a) coformycin, an inhibitor of AMP deaminase, prevented the effects on nucleotide pools, and (b) 3-deazaadenine decreased the conversion of carbocyclic adenosine to carbocyclic ATP and increased its conversion to carbocyclic GTP. The latter conversion requires the action of AMP deaminase and the observed effects can be rationalized by a nucleoside analog-mediated increase in AMP deaminase activity. Because these effects on nucleotide pools are produced only by concentrations higher than those required to inhibit adenosylhomocysteine hydrolase, they may not contribute significantly to the biological effects of 3-deazaadenosine or carbocyclic 3-deazaadenosine.(ABSTRACT TRUNCATED AT 400 WORDS)

AMP Deaminase↗
PubMed1991

Structure-activity relationship of ligands of human plasma adenosine deaminase2.

Diethylaminoethyl-cellulose chromatography was used to separate the two isoenzymes of adenosine deaminase (EC3.5.4.4), adenosine deaminase1 (ADA1) and adenosine deaminase2 (ADA2), in human plasma. One hundred and fifteen purine base, nucleoside, and nucleotide analogs were tested as inhibitors of this partially purified preparation of ADA2. Coformycin and 2'-deoxycoformycin were by far the most potent inhibitors of this isoenzyme (apparent Ki values 20 and 19 nM, respectively). ADA2 was also inhibited by nebularine (apparent Ki 1.5 mM) but was resistant to the potent ADA1 inhibitor (+)-erythro-9(2-S-hydroxy-3-R-nonyl)adenine. alpha-D-Adenosine also inhibited ADA2, as did several halogenated purine and adenine base analogs. Structural requirements for the binding of purine analogs to ADA2 are presented which provide a general basis for the design of specific inhibitors of ADA2. Such inhibitors may be useful in studies designed to provide an understanding of the physiological role of ADA2 both in the normal state and in diseases such as human immunodeficiency virus-1 infection where levels in plasma are increased markedly.

Adenosine Deaminase↗
PubMed1983

Biological effects of incorporation of O6-methyldeoxyguanosine into Chinese hamster V79 cells.

Analysis of the biological effects of specific DNA alkylations by simple alkylating agents is complicated by the variety of sites involved. It is, therefore, of value to be able to incorporate into cellular DNA nucleosides alkylated in a single position, e.g., O6-methyldeoxyguanosine. Such cellular incorporation is particularly difficult to achieve because this nucleoside is rapidly demethylated by adenosine deaminase. We have attempted to achieve such incorporation into the DNA of V79 cells by using coformycin, an inhibitor of adenosine deaminase, and by forcing the cells to depend on exogenous purines by the use of medium containing aminopterin. The DNA of V79 cells exposed to O6-methyl-[8-3H]deoxyguanosine (2.4 microM, sp. act. 14500 Ci/mole) showed an incorporation level of 4 X 10(-8) nucleotides. When 1000-fold higher concentrations were employed (3-15 mM, sp. act. 1.6 Ci/mole), significant cytotoxicity and inhibition of DNA synthesis was observed. However, because it was not economically feasible to administer high specific activity O6-methyldeoxyguanosine to the cells at these concentrations, we could not determine the amount of labeled nucleoside incorporated into DNA. Examination of the frequency of 6-thioguanine-resistant cells in these treated populations showed no significant increase above the background level. Comparison of the cytotoxic effect of O6-methyldeoxyguanosine with deoxyadenosine showed that the toxicity induced by O6-methyldeoxyguanosine could have resulted from mimicry of deoxyadenosine, rather than by incorporation of the alkylated nucleoside itself.

Adenosine Deaminase Inhibitors↗
PubMed1987

Hamster cells with increased rates of DNA amplification, a new phenotype.

Baby hamster kidney (BHK) cells selected simultaneously with N-phosphonacetyl-L-aspartate (PALA) and methotrexate (MTX) gave rise to doubly resistant colonies at frequencies 20 to 260 times greater than the product of the independent frequencies found with PALA or MTX alone. Double resistance was due to amplification of both target genes, CAD and DHFR. Four independent doubly resistant "MP" lines were selected and characterized. Cells resistant to coformycin, pyrazofurin, or ouabain were generated from all four MP lines at rates up to 25 times greater than the rates for BHK cells. These three drugs select cells that have amplified the genes for their target enzymes. Therefore, we conclude that the four MP lines have an amplificator phenotype. All four grew much more slowly than BHK cells, indicating that the amplificator phenotype may be linked to significant defects in metabolism or cell division.

Amides↗
PubMed1983

Double-stranded RNA-stimulated enzyme activities isolated from human placental extracts.

A (2'-5')An synthetase activity was isolated from human placental extracts by affinity chromatography on poly(rI) . poly(rC)-agarose. The oligonucleotide (2'-5')An was identified by (1) chromatography on PEI-cellulose and DEAE-cellulose, (2) inhibition of polypeptide synthesis in lysed rabbit reticulocytes (3) competition of the binding of pppA(pA)3,3'-[32P]pCp to rabbit reticulocyte lysates, and (4) alkaline phosphatase digestion. The synthetase activity in most placental preparations is activated by natural or synthetic dsRNA. However, in a few placental synthetase preparations, dsRNA is only marginally stimulatory and only becomes effective by prior treatment of the enzyme preparations with the calcium-dependent micrococcal nuclease. This suggests that there is an endogenous placental dsRNA contaminant in the enzyme preparations. In some synthetase preparations, a second dsRNA-stimulated product, tentatively identified as the nucleotide 5'-IMP, is also observed. Because the specific AMP deaminase inhibitor coformycin (10 microM) blocks the formation of IMP from ATP and causes a quantitative accumulation of AMP, and because the formation of IMp becomes independent of dsRNA when ADP or AMP is used in place of ATP, the presence of a dsRNA-stimulated ATP phosphohydrolase (ATPase) activity in human placenta is suggested.

2',5'-Oligoadenylate Synthetase↗
PubMed1987

Pathways of adenine nucleotide catabolism in primary rat muscle cultures.

The pathways of AMP degradation and the metabolic fate of adenosine were studied in cultured myotubes under physiological conditions and during artificially induced enhanced degradation of ATP. The metabolic pathways were gauged by tracing the flow of radioactivity from ATP, prelabelled by incubation of the cultures with [14C]adenine, into the various purine derivatives. The fractional flow from AMP to inosine through adenosine was estimated by the use of the adenosine deaminase (EC 3.5.4.4) inhibitors, coformycin and 2'-deoxycoformycin. The activities of the enzymes involved with AMP and adenosine metabolism were determined in cell extracts. The results demonstrate that under physiological conditions, there is a small but significant flow of label from ATP to diffusible bases and nucleosides, most of which are effluxed to the incubation medium. This catabolic flow is mediated almost exclusively by the activity of AMP deaminase (EC 3.5.4.6), rather than by AMP 5'-nucleotidase (EC 3.1.3.5), reflecting the markedly higher Vmax/Km ratio for the deaminase. Enhancement of ATP degradation by inhibition of glycolysis or by combined inhibition of glycolysis and of electron transport resulted in a markedly greater flux of label from adenine nucleotides to nucleosides and bases, but did not alter significantly the ratio between AMP deamination and AMP dephosphorylation, which remained around 19:1. Combined inhibition of glycolysis and of electron transport resulted, in addition, in accumulation of label in IMP, reaching about 20% of total AMP degraded. In the intact myotubes at low adenosine concentration, the anabolic activity of adenosine kinase was at least 4.9-fold the catabolic activity of adenosine deaminase, in accord with the markedly higher Vmax/Km ratio of the kinase for adenosine. The results indicate the operation in the myotube cultures, under various rates of ATP degradation, of the AMP to IMP limb of the purine nucleotide cycle. On the other hand, the formation of purine bases and nucleosides, representing the majority of degraded ATP, indicates inefficient activity of the IMP to AMP limb of the cycle, as well as inefficient salvage of hypoxanthine under these conditions.

5'-Nucleotidase↗
PubMed1987

Determination of nucleotides, nucleosides and nucleobases in cells of different complexity by reversed-phase and ion-pair high-performance liquid chromatography.

Procedures are presented for the analysis of profiles of purine and pyridine compounds in human and rabbit red blood cells by reversed-phase high-performance liquid chromatography and in Ehrlich ascites tumour cells of mouse by ion-pair high-performance liquid chromatography. These compounds are present in rabbit erythrocytes in higher concentrations than in human blood cells, and in rabbit reticulocytes the concentration of purine compounds is still higher. During glucose-free incubation, human red cells accumulate adenosine and adenine in the presence of coformycin owing to the inhibition of adenosine and AMP deamination. Ehrlich ascites tumour cells lose major portions of purine mono-, di- and triphosphates between the seventh and eleventh day after inoculation into mouse peritoneal cavities.

Animals↗
PubMed1979

Evidence that xylosyladenine affects methylation by inhibition of S-adenosyl-L-methionine synthesis.

The adenosine analogs, 9-beta-D-xylofuranosyladenine (XA) and 3'-deoxyadenosine (cordycepin) were tested for their ability to interfer with S-adenosyl-L-methionine (SAM) formation in L1210 cells in vitro. XA inhibited the incorporation of [3H]methionine into SAM in a mixed-competitive manner, while cordycepin was not inhibitory. The adenosine deaminase inhibitor, 2-deoxy-coformycin produced a marked potentiation of the inhibitory effect of XA on Sam synthesis, but did not affect the inactivity of cordycepin. These results indicate that the inhibitory action of XA, but not cordycepin, on the methylation of nuclear RNA may be attributed to interference with the synthesis of SAM.

Adenosine↗
PubMed1999

The design and synthesis of inhibitors of adenosine 5'-monophosphate deaminase.

Carbocylic coformycin (4) is a potent herbicide whose primary mode of action involves inhibition of adenosine 5'-monophosphate deaminase (AMPDA) following phosphorylation of the 5'-hydroxyl group in vivo. The search for more stable and accessible structures led to the synthesis of carbocyclic nebularine (8) and deaminoformycin (10). The latter compound is a good herbicide and its corresponding 5'-monophosphate 14 is a strong inhibitor of plant AMPDA (IC50 100 nM).

AMP Deaminase↗
PubMed1991

The mechanism of adenosine to inosine conversion by the double-stranded RNA unwinding/modifying activity: a high-performance liquid chromatography-mass spectrometry analysis.

We have used directly combined high-performance liquid chromatography-mass spectrometry (LC/MS) to examine the mechanism of the reaction catalyzed by the double-stranded RNA unwinding/modifying activity [Bass & Weintraub (1988) Cell 55, 1089-1098]. A double-stranded RNA substrate in which all adenosines were uniformly labeled with 13C was synthesized. An LC/MS analysis of the nucleoside products from the modified, labeled substrate confirmed that adenosine is modified to inosine during the unwinding/modifying reaction. Most importantly, we found that no carbons are exchanged during the reaction. By including H2(18)O in the reaction, we showed that water serves efficiently as the oxygen donor in vitro. These results are consistent with a hydrolytic deamination mechanism and rule out a base replacement mechanism. Although the double-stranded RNA unwinding/modifying activity appears to utilize a catalytic mechanism similar to that of adenosine deaminase, coformycin, a transition-state analogue, will not inhibit the unwinding/modifying activity.

Adenosine↗
PubMed1985

Study on the inhibition of adenosine deaminase.

4(R)-(1-Hydroxyethyl)-5-methyl-1-beta-D-ribofuranosylimidazole (10), which contains only the asymmetric alcohol center of the diazepinol ring of the adenosine deaminase inhibitor coformycin (12), is a much less potent inhibitor of the enzyme but still binds to the enzyme about as tightly as the normal substrate.

Adenosine↗
PubMed2000

AMP deaminase inhibitors. 2. Initial discovery of a non-nucleotide transition-state inhibitor series.

A series of N3-substituted coformycin aglycon analogues are described that inhibit adenosine 5'-monophosphate deaminase (AMPDA) or adenosine deaminase (ADA). The key steps involved in the preparation of these compounds are (1) treating the sodium salt of 6, 7-dihydroimidazo[4,5-d][1,3]diazepin-8(3H)-one (4) with an alkyl bromide or an alkyl mesylate to generate the N3-alkylated compound 5 and (2) reducing 5 with NaBH(4). Selective inhibition of AMPDA was realized when the N3-substituent contained a carboxylic acid moiety. For example, compound 7b which has a hexanoic acid side chain inhibited AMPDA with a K(i) = 4.2 microM and ADA with a K(i) = 280 microM. Substitution of large lipophilic groups alpha to the carboxylate provided a moderate potency increase with maintained selectivity as exemplified by the alpha-benzyl analogue 7j (AMPDA K(i) = 0.41 microM and ADA K(i) > 1000 microM). These compounds, as well as others described in this series of papers, are the first compounds suitable for testing whether selective inhibition of AMPDA can protect tissue from ischemic damage by increasing local adenosine concentrations at the site of injury and/or by minimizing adenylate loss.

AMP Deaminase↗
PubMed1987

Adenine nucleotide metabolism in isolated chicken hepatocytes.

The turnover of the adenine nucleotide pool, the pathway of the degradation of AMP and the occurrence of recycling of adenosine were investigated in isolated chicken hepatocytes, in which the adenylates had been labelled by prior incubation with [14C]adenine. Under physiological conditions, 85% of the IMP synthesized by the 'de novo' pathway (approx. 37 nmol/min per g of cells) was catabolized directly via inosine into uric acid, and 14% was converted into adenine nucleotides. The latter were found to turn over at the rate of approx. 5 nmol/min per g of tissue. Inhibition of adenosine deaminase by 1 microM-coformycin had no effect on the formation of labelled uric acid, indicating that the initial degradation of AMP proceeds by way of deamination rather than dephosphorylation. Inhibition of adenosine kinase by 100 microM-5-iodotubercidin resulted in a loss of labelled ATP, demonstrating that adenosine is normally formed from AMP but is recycled. Unexpectedly, 5-iodotubercidin did not decrease the total concentration of ATP, indicating that the loss of adenylates caused by inhibition of adenosine kinase was nearly completely compensated by formation of AMP de novo. Anoxia induced a greatly increased catabolism of the adenine nucleotide pool, which proceeded in part by dephosphorylation of AMP. On reoxygenation, the formation of AMP de novo was increased 8-fold as compared with normoxic conditions. The latter results indicate the existence of adaptive mechanisms in chick liver allowing, when required, channelling of the metabolic flux through the 'de novo' pathway, away from the uricotelic catabolic route, into the synthesis of adenine nucleotides.

Adenine Nucleotides↗
PubMed1979

Adenine aminohydrolase: occurrence and possible significance in trypanosomid flagellates.

Adenine aminohydrolase (EC 3.5.4.2) from four species of Leishmania and from Crithidia fasciculata was examined for specific activities, affinity for substrate (adenine), and stability to heat. All were found to be strongly and non-competitively inhibited by both coformycin and deoxycoformycin, two tight-binding inhibitors of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4). Deoxycoformycin is the more potent inhibitor of the two. Neither inhibitor was active against the purine phosphoribosyltransferases. When deoxycoformycin was added to the defined growth medium containing hypoxanthine as the purine source, the growth of C. fasciculata was unaffected, but when adenine was the purine source for the organism, severe inhibition resulted. This implies that hypoxanthine is the obligatory base for nucleotide synthesis and that the adenine phosphoribosyltransferase (AMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.7) is, in some manner,idenied access to exogenous substrate.

Adenosine Deaminase↗
PubMed1982

Mechanism of deoxyadenosine-induced catabolism of adenine ribonucleotides in adenosine deaminase-inhibited human T lymphoblastoid cells.

Loss of ATP accompanying accumulation of dATP has recently been reported to occur in the erythrocytes and lymphoblasts of patients with T lymphocytic leukemia during treatment with deoxycoformycin, an inhibitor of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4) that causes the accumulation of deoxyadenosine. We have studied the mechanisms responsible for adenine ribonucleotide depletion in cultured human CEM T lymphoblastoid cells treated with deoxycoformycin and deoxyadenosine. Accumulation of dATP was accompanied by depletion of total soluble adenine ribonucleotides without change in the adenylate energy charge, by the route ATP --> AMP --> IMP --> inosine --> hypoxanthine; conversion of IMP to AMP and de novo purine synthesis were inhibited in these cells. ATP degradation did not occur in a mutant of CEM that was incapable of phosphorylating deoxyadenosine, or in a B cell line with very limited ability to accumulate dATP. We found that dATP and ATP were both able to stimulate markedly the deamination of AMP by lymphoblast AMP deaminase; dAMP was a poor substrate for this enzyme (K(m) = 2.4 mM, vs. 0.4 mM for AMP). Similarly, dATP as well as ATP caused marked activation of IMP dephosphorylation by a lymphoblast cytoplasmic nucleotidase. Inhibition of intracellular AMP deaminase with coformycin prevented degradation of adenine ribonucleotides without affecting dATP accumulation. We propose that ATP-dependent phosphorylation of deoxyadenosine generates ADP and AMP. Simultaneously, dATP accumulation stimulates deamination of AMP, but not dAMP, and the dephosphorylation of IMP to inosine. Coupling of AMP degradation to ATP utilization in deoxyadenosine phosphorylation maintains the adenylate energy charge despite net depletion of cellular ATP.

5'-Nucleotidase↗
PubMed1980

Capping and adenosine metabolism. Genetic and pharmacologic studies.

Capping of membrane Ig was studied in lymphocytes treated with agents that interfere with adenosine metabolism. Treatment of murine or human B cells with combinations of coformycin, an inhibitor of adenosine deaminase, homocysteine, and adenosine impaired Ig capping. Inhibition of capping was also produced by 3-deazaadenosine, a specific inhibitor of adenosylhomocysteine hydrolase. The inhibitors did not affect capping of the Thy-1 antigen or membrane sites reactive with antilymphocyte antibodies. Two patients with a hereditary deficiency in adenosine deaminase had impairment of Ig capping. Such an impairment was not found in lymphocytes of two other patients who had undergone successful bone marrow transplantation. It is known that the addition of a calcium ionophore results in activation of microfilament function and in disruption of Ig caps. The ionophore effect was not inhibited by the agents mentioned above. Our results suggest that the inhibition of Ig capping during aberrant adenosine metabolism may be caused by a methylation defect preceding the contracticle event that produces membrane reorganization.

Adenosine↗
PubMed1985

Characterization of adenosine deaminase from normal human epidermis and squamous cell carcinoma of the skin.

We compared the characteristics of adenosine deaminases (ADs) (E.C. 3.5.4.4.) in squamous cell carcinoma and normal human epidermis. Increased specific activity (per mg protein) of AD was observed in squamous cell carcinoma compared with that of the normal epidermis. In normal human epidermis most of the AD existed as a large form (Mr 300,000-350,000, type A). Squamous cell carcinoma of the skin was characterized by a high proportion of small-form (Mr 30,000-40,000, type C) AD. The proportion of the small-form enzyme varied from tumor to tumor. Comparison of the large-form AD from squamous cell carcinoma to that from normal epidermis revealed that both enzymes were similar in relative substrate specificity, Km values for adenosine, pH optima, heat stability pattern, isoelectric point, and sensitivity to inhibition by coformycin, a tight binding inhibitor of AD. However, the low molecular weight of AD from squamous cell carcinoma was less heat stable than that from the large-molecular-weight form. Increased AD activity and the high proportion of the small form of AD might be significant features of squamous cell carcinoma of the skin.

Adenosine Deaminase↗