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

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Query: EC:3.5.4.4 (adenosine deaminase)
5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Profiles of the catabolism of adenine nucleotides in cultured plant cells were investigated. Adenine nucleotides, prelabelled by incubation of suspension-cultured Catharantus roseus cells with [8-14C]adenosine, were catabolized rapidly and most of the radioactivity appeared in 14CO2. Allantoin and allantoic acid, intermediates of the oxidative catabolic pathway of purines, were temporarily labelled. When the cells, prelabelled with [8-14C]adenosine, were incubated with high concentrations of adenosine, the rate of catabolism of adenine nucleotides increased. The results suggest that the relative rate of catabolism of adenine nucleotides is strongly dependent on the concentration of adenine nucleotides in the cells. Studies using allopurinol, coformycin and tiazofurin, inhibitors of enzymes involved in purine metabolism, suggest that participation of AMP deaminase and xanthine oxidoreductase in the catabolism of adenine nucleotides in plant cells. AMP deaminase was found in extracts from C. roseus cells and its activity increased significantly in the presence of ATP. In contrast, no adenosine deaminase or adenine deaminase activity was detected. Qualitative differences in the catabolic activity of AMP were observed between suspension-cultured cells from different species of plants.
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PMID:Catabolism of adenine nucleotides in suspension-cultured plant cells. 201 71

Of the dideoxynucleosides described to date, the purine analogues ddA and ddI have exhibited very favorable therapeutic ratios in vitro. ddI is presently undergoing extensive phase I-II clinical trials. Whereas the action of adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) is usually to convert a given analogue of Ado to an inactive or less active form, ddI appears to retain the same biological activity as that of the parent ddA. An explanation for these observations was possible when we found that ddI (1) underwent only a slow cleavage to hypoxanthine through the action of PNP and (2) accumulated the same active antiviral metabolite (i.e., ddATP) as ddA in human lymphoid cells. The use of human lymphoid cells with deficiencies in cellular nucleoside kinases and of inhibitors of pathways of nucleotide metabolism have also revealed new aspects of dideoxypurine metabolism in human lymphoid cells, including the identification of a salvage pathway (phosphotransferase/5'-nucleotide pathway) by which ddA/ddI may be metabolized preferentially to the active nucleotide. The effectiveness of ddA and ddI as orally administered antiviral agents may be limited by their susceptibility to acid hydrolysis and the low efficiency for nucleotide conversion in human lymphoid cells. The presence of a fluorine atom in the arabinose configuration on C-2 confers resistance to solvolysis and renders the analogue less susceptible to enzymatic deamination and resistant to phosphorylytic cleavage by PNP. In addition, human lymphoid cells accumulated several fold higher levels of the putative active triphosphate, 2'-F-dd-ara-ATP, than those of ddA or ddI. This increased accumulation of the analogue triphosphate could be accounted for by a more direct conversion of 2'-F-dd-ara-A by a direct phosphorylation through dCyd kinase than ddA. Thus, a single substitution with fluorine at the 2' "up" position of the sugar moiety of ddA markedly improves several biochemical properties relating to dideoxynucleotide accumulation in human lymphoid cells. Whether there are significant alterations of other biochemical properties, such as the ability of the analogue triphosphate to interact with the target enzyme reverse transcriptase, has not yet been determined. Thus, a definitive resolution of the relative merit of ddA/ddI and its 2'-fluoro-arabinosyl analogue is not yet possible on the basis of the studies described here.
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PMID:Metabolism in human leukocytes of anti-HIV dideoxypurine nucleosides. 207 20

Inherited deficiency of the purine salvage enzyme adenosine deaminase (ADA) is responsible for approximately half the cases of autosomal recessive Severe Combined Immunodeficiency (SCID). Deficiency of ADA can also result in a much later-onset, milder immunodeficiency, while lesser degrees of enzyme deficiency can result in either late-onset immunodeficiency or grossly normal immunologic function. The full clinical spectrum of ADA deficiency is currently being more fully defined. Florid pathology is primarily restricted to the immune system and appears to result from accumulation of substrates (adenosine and deoxyadenosine) and metabolites (deoxy ATP). Studies indicate that these metabolites may preferentially accumulate in lymphoid cells and can interfere with lymphoid proliferation and function. There is evidence for several mechanisms, including induction of chromosome breaks, inhibition of ribonucleotide reductase needed for normal DNA synthesis, and inactivation of SAH hydrolase needed for normal methylation reactions. The enzyme is a 40 Kd monomer that is ubiquitous, and diagnosis can be made with many cell types including erythrocytes, lymphocytes and fibroblasts. Prenatal diagnosis has been made with chorionic villous samples, amniotic cells and fetal blood. The gene for ADA resides on the long arm of human chromosome 20, and both the expressed and structural gene have been isolated and characterized. Most patients with ADA SCID have single base pair mutations resulting in amino acid substitutions, although a splicing mutation and a deletion have been described. The treatment of choice is currently bone-marrow transplantation from a histocompatible related donor, if available. Haploidentical transplants have also been successful but appear to have higher failure rates in ADA deficients than in other types of SCID. Enzyme replacement, now using an enzyme modified to increase the half-life and decrease immunogenicity, has been reported as successful but longer-term efficacy remains to be evaluated. The disorder, despite its rarity, is for several reasons considered a prime candidate for gene therapy. Recently success has been obtained in introducing the gene into lymphoid stem cells and achieving long-term expression.
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PMID:Adenosine deaminase deficiency. 207 32

Our earlier work on reperfusion showed that adult rat hearts released almost twice as much purine nucleosides and oxypurines as newborn hearts did [Am J Physiol 254 (1988) H1091]. A change in the ratio anabolism/catabolism of adenosine could be responsible for this effect. We therefore measured the activity of adenosine kinase, adenosine deaminase, nucleoside phosphorylase and xanthine oxidoreductase in homogenates of hearts and myocytes from neonatal and adult rats. In hearts the activity of adenosine deaminase and nucleoside phosphorylase (10-20 U/g protein) changed relatively little. However, adenosine kinase activity decreased from 1.3 to 0.6 U/g (P less than 0.025), and xanthine oxidoreductase activity increased from 0.02 to 0.85 U/g (P less than 0.005). Thus the ratio in activity of these rate-limiting enzymes for anabolism and catabolism dropped from 68 to 0.68 during cardiac development. In contrast, the ratio in myocytes remained unchanged (about 23). The large difference in adenosine anabolism/catabolism ratio, observed in heart homogenates, could explain why ATP breakdown due to hypoxia is lower in neonatal than in adult heart. Because this change is absent in myocytes, we speculate that mainly endothelial activities of adenosine kinase and xanthine oxidoreductase are responsible for this shift in purine metabolism during development.
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PMID:Ischemic nucleotide breakdown increases during cardiac development due to drop in adenosine anabolism/catabolism ratio. 209 32

Severe combined immunodeficiency disease (SCID) with adenosine deaminase (ADA) deficiency is a genetic autosomic recessive disorder with profound impairment of T-cell function, invariably complicated by fatal infections. The absence of ADA-enzyme and the accumulation of deoxy-ATP, with toxic effects on the T-lymphocytes is the common feature of this disease. As a consequence, lymphoid precursors failure to develop into mature T-cells, resulting in absolute lymphopenia and atrophy of the thymus. Bone marrow transplantation from an HLA-identical donor is considered the treatment of choice for this disease. We describe the case of a 1-month-old child with ADA deficiency SCID who underwent bone marrow transplantation (BMT) using paternal haploidentical, lectin-separated marrow, as a source of hemopoietic stem cells.
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PMID:Successful lectin-separated bone marrow transplantation in adenosine deaminase deficiency-related severe immunodeficiency. 209 97

In isolated hepatocytes from fasted rats, 0.5 mM adenosine inhibited gluconeogenesis from glutamine, lactate and pyruvate. This inhibition was due to adenosine conversion through adenosine kinase. An increase in ketone body release was only observed in the presence of lactate or pyruvate, and the two phenomena (i.e. inhibition of gluconeogenesis and increased ketone-body release) were linked. With alanine, dihydroxyacetone or serine as substrates, adenosine did not change gluconeogenesis; however, its conversion through adenosine kinase also inhibited gluconeogenesis. With asparagine as substrate, 0.5 mM adenosine increased gluconeogenesis; this increase was due to adenosine conversion through adenosine deaminase. However, adenosine conversion through adenosine kinase inhibited gluconeogenesis from asparagine. Thus, whatever the substrate used, adenosine conversion through adenosine kinase inhibited gluconeogenesis. The inhibitory effect of adenosine on gluconeogenesis cannot be related to the decrease in Pi concentration and to the increase in ATP pool. Beside its effect on gluconeogenesis, adenosine inhibited ketogenesis measured without added substrate; adenosine conversion through adenosine kinase was also involved in the inhibition of ketogenesis.
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PMID:Metabolism of adenosine through adenosine kinase inhibits gluconeogenesis in isolated rat hepatocytes. 215 47

H2O2-mediated cytotoxicity (as measured by 51Cr-release) of rat pulmonary artery endothelial cells was time-dependent and related to the concentration of H2O2 employed. The cytotoxic effects of H2O2 were, as expected, prevented by catalase and the degree of protection was directly related to its time of addition. Endothelial cells were incubated with [14C]adenosine to achieve intracellular labeling of ATP, after which the cells were exposed to H2O2. Based on analysis of cell extracts by high-performance liquid chromatography, there was a time-dependent loss of intracellular radioactivity and ATP with the simultaneous appearance of purine degradation products including xanthine/hypoxanthine. Approximately 50% of the intracellular ATP was lost after 15 minutes of exposure and up to 80% was lost by 30 minutes. The extracellular fluid of cells exposed to H2O2 contained significant amounts of xanthine/hypoxanthine. The ferric iron chelator deferoxamine provided almost complete protection against H2O2-mediated cytotoxicity. Two inhibitors of xanthine oxidase, allopurinol and oxypurinol, were also protective as was deoxycoformycin, an inhibitor of adenosine deaminase. Remarkably, cells protected by these agents showed the same loss of intracellular ATP as unprotected, H2O2-treated cells. These findings demonstrate the dissociation between ATP loss per se and oxidant injury of endothelial cells. ATP breakdown may be an important event leading to cellular injury in that this results in the formation of substrate for xanthine oxidase.
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PMID:H2O2-mediated cytotoxicity of rat pulmonary endothelial cells. Changes in adenosine triphosphate and purine products and effects of protective interventions. 217 53

Incubation of rat adipocytes with 1 microM glucagon plus adenosine deaminase (5 micrograms/ml) inhibited maximally insulin-stimulated 3-O-methyl-D-glucose (MeGlc) transport by approximately 70%, concomitant with 30% and 55% decreases in insulin binding and cellular ATP, respectively. In contrast, under conditions where cellular ATP levels are well preserved (i.e. high albumin concentration in the medium), the inhibition of transport was reduced to about 30%, but that of insulin binding was not. Because depletion of the cellular ATP level by more than 60% by metabolic inhibitors induced 40% or more inhibition of insulin-stimulated MeGlc transport, the greater inhibition of the transport with the low albumin concentration appears to be caused in part by the secondary effect of ATP loss. The relationship between the amount of cell-bound insulin and hormone-stimulated transport activity showed that glucagon does not modulate insulin action at the step of insulin binding to its receptors. Furthermore, glucagon suppressed insulin-stimulated MeGlc transport, mainly through an attenuation of the hormone-induced increase in maximum velocity. The data show that glucagon modulates the process of signal transduction of insulin action. However, the possibility that glucagon directly modulates the process of translocation or the intrinsic activity of the glucose transporters cannot be eliminated.
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PMID:Glucagon inhibits insulin activation of glucose transport in rat adipocytes mainly through a postbinding process. 220 31

The aim of this study was to determine the dual role of ATP as an energy substrate and as a major source of oxygen-derived free-radical-mediated reperfusion injury by using adenine nucleoside blocker, p-nitrobenzylthioinosine (NBMPR), and adenosine deaminase inhibitor, erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA). In a randomized study, 16 dogs were instrumented with minor-axis LTZ-piezoelectric crystals and intraventricular pressure transducers to monitor, off bypass, left ventricular performance by using a sensitive and load-independent index of contractility (slope of the stroke work-end-diastolic length relation). Hearts were subjected to 60 minutes of normothermic global ischemia and 120 minutes of reperfusion. Normal saline without (Group 1, n = 8) or with (Group 2, n = 8) NBMPR and EHNA was infused in three boluses into the cardiopulmonary bypass reservoir before ischemia and reperfusion. Transmural serial biopsies were obtained before and during ischemia and reperfusion and analyzed for myocardial adenine nucleotide pool intermediates by using high-performance liquid chromatography. In the control group, three hearts developed ischemic contracture and another three hearts exhibited cardiogenic shock during reperfusion. In the EHNA/NBMPR-treated group, left ventricular performance recovered within 30 minutes of reperfusion (p less than 0.05 vs. control). Myocardial ATP was depleted to 20% of normal in both groups by the end of ischemia (p less than 0.05). Intramyocardial adenosine in the EHNA/NBMPR-treated group was 12-fold greater (15.09 +/- 1.6 nmol/mg protein) than the control group at the end of the ischemic period (p less than 0.05). Inosine was about fourfold higher in the control group (19.07 +/- 1.50 nmol/mg protein) compared with the drug-treated group (p less than 0.05). During reperfusion, myocardial ATP levels increased to approximately 50% of normal in the EHNA/NBMPR group while remaining depressed (20% of normal) in the control group. Thus, despite the dramatic loss of myocardial ATP during ischemia, complete recovery of ventricular performance and significant repletion of ATP during reperfusion were observed when adenosine transport and deamination were modulated during ischemia and reperfusion. These results suggest that 1) the myocardium may have more ATP than is needed for basic cardiac functions and 2) washout of ATP diffusible catabolites is detrimental to ventricular performance during reperfusion. Specific blockade of nucleoside transport resulted in complete functional recovery despite low but critical ATP levels.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Is adenosine 5'-triphosphate derangement or free-radical-mediated injury the major cause of ventricular dysfunction during reperfusion? Role of adenine nucleoside transport in myocardial reperfusion injury. 193 94

Rat soleus muscle strips cultured for 24 h in medium 199 were well preserved in terms of electron microscopy; ATP and creatine phosphate concentrations; rates of glucose utilization, glycogen and protein synthesis, and effects of insulin thereon. Culture led to modest changes in fluid spaces and intracellular (K+); increased basal glucose utilization up to two-fold; had no effect on the maximum response to insulin; and had no effect on sensitivity to insulin except in the presence of adenosine deaminase. Thus in vitro neither denervation nor absence of insulin had any marked effects in 24 h to decrease responses to insulin.
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PMID:Long term culture of rat soleus muscle in vitro. Its effects on glucose utilization and insulin sensitivity. 222 70


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