PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Coformycin”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 19 recordsLinked to original sources
PubMed1990

The rate constant describing slow-onset inhibition of yeast AMP deaminase by coformycin analogues is independent of inhibitor structure.

(R)- and (S)-2'-deoxycoformycin, (R)-coformycin, and the corresponding 5'-monophosphates were compared as inhibitors of yeast AMP deaminase. The overall inhibition constants ranged from 4.2 mM for (S)-2'-deoxycoformycin to 10 pM for (R)-coformycin 5'-monophosphate, a difference of 3.8 x 10(8) in affinities. (R)-Coformycin, (R)-2'-deoxycoformycin 5'-monophosphate, and (R)-coformycin 5'-monophosphate exhibited both rapid and slow-onset inhibition. The S inhibitors and (R)-2'-deoxycoformycin exhibited classical competitive inhibition but no time-dependent onset of inhibition. The results indicate that the presence of the 2'-hydroxyl and 5'-phosphate and the R stereochemistry at the C-8 position of the diazepine ring are necessary for the optimum interaction of inhibitors with yeast AMP deaminase. This differs from the results for rabbit muscle AMP deaminase [Frieden C., Kurz, L. C., & Gilbert, H. R. (1980) Biochemistry 19, 5303-5309] and calf intestinal adenosine deaminase [Schramm, V. L., & Baker, D. C. (1985) Biochemistry 24, 641-646], in which a tetrahedral hydroxyl at C-8 in the R stereochemistry is sufficient for slow-onset inhibition with the coformycins. The results suggest that the transition state contains a tetrahedral carbon with the R configuration as a result of the direct attack of an oxygen nucleophile at C-6 of AMP. Slow-onset inhibition of yeast AMP deaminase is consistent with the mechanism [formula: see text] in which the combination of E and I is rapidly reversible. For these inhibitors, Ki varied by a factor of 3 x 10(3), and the overall inhibition constant (Ki*) varied by a factor of 2 x 10(5).(ABSTRACT TRUNCATED AT 250 WORDS)

AMP Deaminase↗
PubMed1992

Effects of adenine arabinoside and coformycin on the kinetics of G2 chromatid aberrations in X-irradiated human lymphocytes.

The kinetics of chromatid aberrations have been studied in human lymphocytes exposed to X-rays in the G2 phase of the cell cycle and incubated with or without the nucleoside analogue 9-beta-D-arabinofuranosyladenine (ara A), known to inhibit the repair of DNA double-strand breaks. In the absence of ara A an exponential decrease in frequencies of chromatid breaks occurred which we interpret as repair. Few breaks were observed if samples were harvested immediately following irradiation. The frequency of chromatid breaks at 1 h after X-irradiation (442 per 100 cells/Gy) was similar to that previously observed in Chinese hamster ovary (CHO) K1 cells. However, the exponential decrease of chromatid breaks between X-irradiation and sampling occurred with a t1/2 of 0.87 h, a faster rate than we have previously observed in CHO K1 cells and was not inhibited by 200 microM ara A alone, in contrast with our previous findings in a human fibroblast line. However, in the presence of the ADA inhibitor coformycin, inhibition of break repair was already observed at an ara A concentration of 100 microM indicating that the apparent unresponsiveness to ara A of lymphocyte chromatid break rejoining results from the deamination of this nucleoside analogue. This deamination effect was confirmed by measurements of DNA synthesis which showed stable inhibition of synthesis by ara A only when coformycin was present. Frequencies of chromatid exchanges in irradiated cells remained constant except at the sampling time directly after irradiation, consistent with the view that chromosomal radiosensitivity remained constant throughout the G2 phase, except for the period immediately prior to mitosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatids↗
PubMed1976

Inhibition of maturation of human precursor lymphocytes by coformycin, an inhibitor of the enzyme adenosine deaminase.

High concentrations of adenosine are known to be toxic to fibroblasts and lymphocytes under conditions of in vitro culture (1,2). Normally, accumulation of adenosine nucleotides in all mammalian cells is prevented by the presence of adenosine deaminase, an aminohydrolase which converts adenosine to inosine (3). A genetically determined deficiency of adenosine deaminase has been associated with the autosomal recessive form of severe combined immunodeficiency, a syndrome in which precursor lymphocytes fail to mature into T cells and B cells (4-7). Erythrocytes of affected infants convert exogenous adenosine to AMP and ATP at an abnormally increased rate as a consequence of the enzyme defect, and ATP at an abnormally increased rate as a consequence of the enzyme defect, and fail to form inosine from the exogenous adenosine (8). These metabolic disturbances can be mimicked in normal erythrocytes by coformycin (8), a potent competitive inhibitor of adenosine deaminase (9, 10). In this study, the effects of coformycin were examined on the in vitro function of normal lymphocytes.

Adenosine Deaminase Inhibitors↗
PubMed1979

Levels of adenosine deaminase in some experimental animal tumours and the possible therapeutic effect of the ADA inhibitor 2-deoxy-coformycin.

The intracellular adenosine deaminase activities (ADA) in 12 different experimental animal tumours were measured. Unlike the leukaemic lymphoblasts of man, those of two spontaneous rat leukaemias did not have elevated levels of the enzyme. Very high levels were found in a rat plasma-cell tumour (IR 461) and an attempt was made to treat such tumours with the specific enzyme inhibitor, 2-deoxy-coformycin. The shortage of this drug prevented a systematic study, but a daily dose of 8 mg/kg had a significant inhibitory effect on the growth of tumours.

Adenosine Deaminase↗
PubMed1990

Coamplification of mu class glutathione S-transferase genes and an adenylate deaminase gene in coformycin-resistant Chinese hamster fibroblasts.

In Chinese hamster fibroblasts, we previously detected an expressed gene located near the AMP deaminase gene. This gene was named Y1. Upon selection for resistance to coformycin, an inhibitor of AMP deaminase activity, both genes were amplified in several mutants. We have determined the complete nucleotide sequence of Y1 cDNA and identified the Y1 gene as a mu class glutathione S-transferase gene by comparison with sequences present in a data bank. Accordingly, Y1-amplified mutants express an increased glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene; this activity, as well as the abundance of the corresponding RNA, appears, however, to reach a limit despite further increase in the Y1 gene copy number during successive amplification steps. Southern blot experiments showed that Y1 belongs to a multigene family, all or part of which has been amplified in mutant lines. These data provide a method to amplify and to overexpress the mu class of the glutathione S-transferase gene family on the basis of its linkage with the AMP deaminase gene.

AMP Deaminase↗
PubMed1976

Antiviral activity of arabinosyladenine and arabinosylhypoxanthine in herpes simplex virus-infected KB cells: selective inhibition of viral deoxyribonucleic acid synthesis in the presence of an adenosine deaminase inhibitor.

The antiviral activity of the fraudulent nucleoside arabinosyladenine (ara-A) against herpes simplex virus (HSV) type 1 was increased nearly 20-fold by the adenosine deaminase inhibitor, coformycin. The combination of ara-A plus coformycin was 90 times more potent in blocking HSV replication than was arabinosylhypoxanthine (ara-H). In suspension culture both drugs were more active than they were in monolayer culture. Deoxyribonucleic acid (DNA) synthesis also was inhibited by the nucleosides. Depending upon the species of DNA examined, ara-A was 8 to 15 times more active in the presence of coformycin, and the combination was 35 to 70 times more potent than ara-H. Both drugs inhibited total DNA synthesis to the same extent in uninfected and HSV-infected KB cells. In contrast, viral DNA synthesis was three to six times more susceptible to inhibition than was cellular DNA synthesis. Inhibition of viral DNA synthesis was more pronounced in suspension culture than in monolayer culture. However, the method of cell propagation did not alter the degree to which the drugs inhibited DNA synthesis in uninfected KB cells. An index has been derived to quantitate the extent of the selective inhibition of viral or cellular DNA synthesis. Fifty percent inhibitory concentrations of a drug were calculated for uninfected KB DNA synthesis and viral DNA synthesis and expressed as a ratio. The logarithm of this ratio was termed the selective index and was positive if viral DNA synthesis was inhibited preferentially or negative if uninfected KB DNA synthesis was more strongly inhibited. Data from experiments performed in monolayer culture gave positive selective index values of 0.3, 0.5, and 0.4 for ara-A plus coformycin, ara-A, and ara-H, respectively. Values of 0.7 and 0.6 were obtained from suspension culture data for ara-A plus coformycin and ara-H, respectively. Considered collectively, the data presented in this communication establish that coformycin increased the potency of ara-A but did not increase its selectivity.

Adenosine Deaminase Inhibitors↗
PubMed1976

Role of adenosine deaminase in lymphocyte proliferation.

Activity of adenosine deaminase (ADA), an enzyme known to be deficient in some patients with severe combined immunodeficiency, increased three-fold within a 24-hour exposure of human peripheral blood lymphocytes to phytohaemagglutinin (PHA) in culture. This increase took place before the onset of DNA synthesis. Increased levels of ADA activity were also observed in lymphocytes incubated with pokeweed mitogen (PWM) for 60 hr. DNA synthesis induced by PHA, PWM or mixed lymphocyte cultures (MLC) was strongly inhibited by adenosine at concentrations of 10(-4) M or higher when human peripheral blood lymphocytes were cultured in a medium supplemented with horse serum, which lacks ADA. 10(-6)-10(-8) M coformycin, a potent inhibitor of ADA, inhibited PHA-, PWM- and MLC-induced DNA synthesis to a variable extent, whereas thymidine incorporation induced by Salmonella lipopolysaccharide (LPS) in mouse spleen cell cultures was strongly inhibited (by 75% or more) by 10(-6) M coformycin. Combination of 10(-7)-10(-8) M coformycin and 10(-4)-10(-5) M adenosine synergistically inhibited mitogen- or MLC-induced DNA synthesis in human and mouse lymphocyte cultures. These results, together with observations on children with ADA deficiency, provide evidence that adenosine deaminase is highly important for lymphocyte proliferation. Human peripheral blood lymphocytes incubated with PHA, 10(-5) M adenosine and 10(-7) M coformycin showed some cytotoxicity whereas the rate of 51Cr release from normal lymphocytes was not modified by the drugs. These findings suggest that in vivo clones of lymphocytes responding to specific antigens might be eliminated by coformycin, which may prove to be useful as a specific immunosuppressive agent.

Adenosine↗
PubMed1979

Studies on inhibition of adenosine deaminase by isocoformycin in vitro and in vivo.

Isocoformycin is a structural isomer of coformycin which has been demonstrated to be a potent inhibitor of adenosine deaminase. Isocoformycin showed a weaker inhibition of this enzyme than coformycin; the binding of coformycin to enzyme was irreversible, but isocoformycin inhibition was competitive with substrate. The Ki value of isocoformycin was 4.5 approximately 10 X 10(-8) M. Following intraperitoneal injection of isocoformycin in mice, the adenosine deaminase activity of homogenates of several organs was determined and the following ED50 values (50% inhibition doses) were observed: 29 mg/kg for thymus, 13 mg/kg for spleen, 80 mg/kg for liver and 20 mg/kg for kidney. The inhibition of adenosine deaminase in rabbit blood in vitro was also tested in comparison with coformycin.

Adenosine Deaminase↗
PubMed1991

Extracellular metabolism of adenine nucleotides and adenosine in the innervated skeletal muscle of the frog.

The effects of coformycin, alpha,beta-methylene ADP, dipyridamole in the absence and presence of erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), nitrobenzylthioinosine (NBTI), mioflazine and ouabain on the metabolic pathways of exogenously applied ATP and its metabolites in the frog innervated sartorius muscle were investigated. ATP catabolism yielded ADP, AMP, IMP, adenosine and inosine; the ecto-ATPase in situ was shown to be Ca(2+)- or Mg(2+)-activated with a Kmapp for ATP of 767 +/- 48 microM. AMP catabolism yielded IMP, adenosine and inosine; inosine was formed from either exogenous IMP or exogenous adenosine. Catabolism of AMP into IMP was blocked by coformycin, which enhanced adenosine and inosine formation from AMP. alpha,beta-Methylene ADP blocked adenosine formation from AMP and inosine formation from IMP; formation of IMP from AMP was enhanced by alpha,beta-methylene ADP. Complete blockade of AMP degradation was achieved with the simultaneous use of coformycin and alpha,beta-methylene ADP. Dipyridamole attenuated but did not completely block extracellular adenosine removal and inosine appearance in the bath. EHNA, applied in the presence of dipyridamole, did not cause any further attenuation of extracellular adenosine removal. Mioflazine, NBTI and ouabain did not affect adenosine disappearance from the bath. The results suggest that, in the frog innervated sartorius muscle, ATP can be sequentially catabolized into AMP which is then catabolized either into IMP or into adenosine. This extracellular degradation of AMP into IMP might then constitute a shunt-like mechanism to control the levels of adenosine formed from adenine nucleotides.

Adenine↗
PubMed1976

Adenosine metabolism in phytohemagglutinin-stimulated human lymphocytes.

The association of a human genetic deficiency of adenosine deaminase activity with combined immunodeficiency prompted a study of the effects of adenosine and of inhibition of adenosine deaminase activity on human lymphocyte transformation and a detailed study of adenosine metabolism throughout phytohemagglutinin-induced blastogenesis. The adenosine deaminase inhibitor, coformycin, at a concentration that inhibited adenosine deaminase activity more than 95%, or 50 muM adenosine, did not prevent blastogenesis by criteria of morphology or thymidine incorporation into acid-precipitable material. The combination of coformycin and adenosine, however, substantially reduced both the viable cell count and the incorporation of thymidine into DNA in phytohemagglutinin-stimulated lymphocytes. Incubation of lymphocytes with phytohemagglutinin for 72 h produced a 12-fold increase in the rate of deamination and a 6-fold increase in phosphorylation of adenosine by intact lymphocytes. There was no change in the apparent affinity for adenosine with either deamination or phosphorylation. The increased rates of metabolism, apparent as early as 3 h after addition of mitogen, may be due to increased entry of the nucleoside into stimulated lymphocytes. Increased adenosine metabolism was not due to changes in total enzyme activity; after 72 h in culture, the ratios of specific activities in extracts of stimulated to unstimulated lymphocytes were essentially unchanged for adenosine kinase, 0.92, and decreased for adenosine deaminase, 0.44. As much as 38% of the initial lymphocyte adenosine deaminase activity accumulated extracellularly after a 72-h culture with phytohemagglutinin. In phytohemagglutinin-stimulated lymphocytes, the principal route of adenosine metabolism was phosphorylation at less than 5 muM adenosine, and deamination at concentrations greater than 5 muM. In unstimulated lymphocytes, deamination was the principal route of adenosine metabolism over the range of adenosine concentrations studied (0.5-250 muM). These studies demonstrate the dependence of both the unstimulated and stimulated lymphocyte on adenosine and may account for the observed sensitivity of mitogen-stimulated lymphocytes to the toxic effects of exogenously supplied adenosine in the presence of the adenosine deaminase inhibitor coformycin. A single case of immunodeficiency disease has been reported in association with purine nucleoside phosphorylase deficiency. The catabolism of guanosine was also found to be enhanced in stimulated normal lymphocytes; phosphorolysis of guanosine to guanine by intact lymphocytes increased six fold after 72-h culture with phytohemagglutinin. The specific activity of purine nucleoside phosphorylase in extracts, with guanosine as substrate, was essentially the same in stimulated and unstimulated lymphocytes after 72 h of culture.

Adenosine↗
PubMed1988

Inhibition of adenosine-metabolizing enzymes modulates mouse sperm fertilizing ability: a changing role for endogenously generated adenosine during capacitation.

The effect of inhibiting adenosine-metabolizing enzymes on sperm fertilizing ability was studied to investigate a possible role for endogenously generated adenosine in the regulation of capacitation. The compounds used have been shown to be effective inhibitors of the relevant enzymes in similarly incubated mouse sperm suspensions. Inhibition of 5'-nucleotidase activity with alpha, beta-methylene adenosine 5'-diphosphate (AMPCP), to reduce available endogenous adenosine, caused a dose-dependent inhibition of the fertilizing ability of partially capacitated spermatozoa, which was significant with 100 and 250 microM AMPCP. Conversely, inhibition of adenosine deaminase with 100 nM coformycin, to increase available endogenous adenosine, promoted the fertilizing ability of partially capacitated spermatozoa when the fertilization rate of control suspensions was low. However, coformycin had no effect on sperm suspensions with moderate fertilizing ability, and it inhibited fertilizing ability when added to capacitated spermatozoa. These data are consistent with a promotion of the early stages of capacitation by endogenously generated adenosine and suggest that sensitivity to adenosine changes as capacitation proceeds. Because the majority of adenosine-metabolizing enzyme activity residues in or is directed toward the extracellular compartment in such suspensions, these effects of adenosine may be mediated at the outer surface of the cell. By interacting with receptors on adenylate cyclase, externally produced adenosine could modulate intracellular levels of cyclic adenosine monophosphate (cAMP), thereby influencing fertilizing ability.

5'-Nucleotidase↗