Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.2.7 (adenine phosphoribosyltransferase)
 692 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Incorporation of the adenine moiety of 2'-deoxyadenosine (dAdo) into ATP, consistently observed in human erythrocytes, is a phenomenon which cannot be explained by the operation of any known pathway. We reported previously that this effect was not observed in adenine phosphoribosyltransferase-deficient erythrocytes showing that adenine must be an obligatory intermediate. However, generation of adenine from dAdo was difficult to reconcile with the operation of any known process in human cells, and involvement of S-adenosylhomocysteine hydrolase (SAH-hydrolase) was postulated. The present studies with intact human erythrocytes demonstrate that nucleoside analogues which inhibit SAH-hydrolase caused substantial attenuation of adenine transfer from dAdo into ATP. It was confirmed that dAdo is not a substrate of 5'deoxy-5'methylthioadenosine (5'MT-adenosine) phosphorylase. Inhibition of the transfer of the adenine moiety of dAdo into ATP did not correlate with inhibition of 5'MT-adenosine phosphorylase by nucleoside analogues. This report provides further evidence that the pathway involving nucleoside (adenosine) analogue binding to SAH-hydrolase, release of base and subsequent phosphoribosylation can operate in intact cells. The metabolic significance of this process relates to the possible generation of free bases (adenine) in the human body, ATP synthesis and nucleoside drug interconversions.
 ...
PMID:A novel route of ATP synthesis. 159 94

Deoxycytidine (dCyd) kinase has been purified to homogeneity from human leukemic spleen, and the capacity of the enzyme to phosphorylate 2',3'-dideoxynucleoside (ddN) analogs that are clinically effective inhibitors of human immunodeficiency virus (HIV) replication was evaluated. Cytosine-containing ddN analogs, such as 2',3'-dideoxycytidine, 2',3'-dideoxy-2',3'-dehydrocytidine, and cytallene, were efficiently phosphorylated by dCyd kinase, while no phosphorylation of purine-containing ddN analogs was detected. dCyd kinase was completely inactive toward 2',3'-dideoxyadenosine (ddAdo), 2',3'-dideoxyinosine, 2',3'-dideoxyguanosine, and adenallene, although it was capable of phosphorylating both 2'-deoxyadenosine (dAdo) and 2'-deoxyguanosine (dGuo). The abilities of wild type and mutant human T lymphoblastoid CEM cells to accumulate ddAdo in situ and in vitro were also ascertained. Comparison of the abilities of intact wild type CEM cells and derivatives deficient in nucleoside transport, dCyd kinase, and/or adenosine (Ado) kinase to accumulate [3H]ddAdo-derived radioactivity revealed no significant differences among the wild type and mutant strains. However, ddAdo phosphorylating activity was decreased in extracts from Ado kinase-deficient cells but not in lysates prepared from cells genetically deficient in dCyd kinase activity. In comparative growth rate experiments, wild type, nucleoside transport-deficient, and dCyd kinase-deficient CEM cells were equally sensitive to ddAdo toxicity, while, interestingly, a deficiency in Ado kinase correlated with a 5-fold decreased growth sensitivity to the purine ddN. Insertion of an adenine phosphoribosyltransferase deficiency into the CEM cell lines did not influence ddAdo toxicity or incorporation rate. These results imply that Ado kinase may be an important factor in ddAdo phosphorylation by CEM cells. Furthermore, these studies demonstrate that cytosine- and purine-containing ddNs are transported and activated by independent pathways and, therefore, have important implications for anti-HIV therapy in that pyrimidine and purine ddNs might be used in combination for the treatment of acquired immunodeficiency syndrome.
 ...
PMID:Substrate specificity of human deoxycytidine kinase toward antiviral 2',3'-dideoxynucleoside analogs. 173 8

Adenosine derivatives are frequently used in chemotherapy because of their potent antitumor, antiviral and antiparasitic activity. We investigated the metabolism of some adenosine analogues in adenosine deaminase inhibited normal and adenine phosphoribosyltransferase (APRT) deficient human erythrocytes. The ATP and GTP concentrations and the formation of unusual nucleotides were measured. Some of the analogues studied (tubercidin, 9 beta-D-arabinofuranosyladenine, 2'-deoxyadenosine, 2-chloroadenosine, neplanocin A) were phosphorylated to the corresponding nucleoside triphosphates and this process was abolished by iodotubercidin--an adenosine kinase inhibitor. With the exception of 2'-deoxyadenosine, nucleotide analogue formation was accompanied by ATP depletion. ATP decrease was not observed after adenosine kinase inhibition and ATP concentration even increased in the presence of 2'-deoxyadenosine, neplanocin A and 5'-iodo-5'-deoxyadenosine. However, the latter increment was not observed in APRT deficient erythrocytes. Bredinin, S-adenosylhomocysteine, deoxycoformycin and adenosine dialdehyde did not form nucleotide derivatives or exert any effects on ATP concentration. It is concluded that adenosine analogues can either enter the nucleotide pool via phosphorylation mechanisms, or may be converted to ATP by the pathways involving the intermediate formation of adenine.
 ...
PMID:Effects of adenosine analogues on ATP concentrations in human erythrocytes. Further evidence for a route independent of adenosine kinase. 193 Mar 1

Of 142 purines, purine nucleosides, and analogues tested for inhibition of growth of Escherichia coli B Hill, 45 were active. Of these, 27 were evaluated for inhibition of other E. coli lines, including those resistant to 6-thioguanine, 2-fluoroadenosine, 2,6-diaminopurine, or 6-mercaptopurine. Most toxic to the parent lines were 2-fluoroadenosine, 2-fluoroadenine, 2-fluoro-5'-deoxyadenosine, adenosine, 6-thioguanosine, 6-thioguanine, 6-mercaptopurine, 6-mercaptopurine ribonucleoside, 2-azaadenine, 2'-deoxyinosine, 6-N-aminoadenine, and inosine. Hypoxanthine was strongly inhibitory only to E. coli B Hill. Evidence regarding the substrate specificity of the three purine phosphoribosyltransferases was obtained by assaying for these enzymes in extracts of the various cell lines and by cross-resistance studies. The line selected for resistance to 6-thioguanine had low guanine phosphoribosyltransferase activity (guanosine monophosphate: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) and was deficient in activity for xanthine and 6-thioguanine. The lines selected for resistance to 2-fluoroadenosine and 2,6-diaminopurine were deficient in adenine phosphoribosyltransferase activity (adenosine monophosphate: pyrophosphate phosphoribosyltransferase, EC 2.4.2.7), and that selected for resistance to 6-mercaptopurine had low hypoxanthine phosphoribosyltransferase activity and undetectable activity with 6-mercaptopurine as a substrate. Purine, 6-methylpurine, 2-fluoroadenine, 2,6-diaminopurine, and 2-azaadenine were classified as adenine analogues; 6-mercaptopurine and 8-aza-2,6-diaminopurine, as hypoxanthine analogues; and 6-thioguanine and 2-amino-6-chloropurine, as analogues of guanine. The inhibition of bacterial growth by hypoxanthine, inosine, 2'-deoxyinosine, or adenosine was prevented by small amounts of thiamine or by relatively high concentrations of either cytidine or uridine. Cytidine also reversed the inhibition by some purine and purine ribonucleoside analogues. Orotate phosphoribosyltransferase (OMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.10), a possible site of action for these compounds, was not inhibited directly by the toxic agents.
 ...
PMID:Use of Escherichia coli mutants to evaluate purines, purine nucleosides, and analogues. 459 16

Variants of Chinese hamster ovary and Novikoff rat hepatoma cells resistant to tubercidin and 2,5-diaminopurine, or to both drugs, were isolated, and their ability to convert adenosine and various adenosine analogs to nucleotides was compared to that of wild-type cells, both in intact cells and cell-free extracts. Adenosine deamination, and thus its conversion to nucleotides via inosine-hypoxanthine-inosine monophosphate, was inhibited by pretreatment of the cells or cell extracts with 2-deoxycoformycin. Cell-free extracts of the tubercidin-resistant variants, as well as of two adenosine-resistant mutants of Chinese hamster ovary cells, phosphorylated adenosine, tubercidin, pyrazofurin, or tricyclic nucleoside in the presence of ATP at less than 1% of the rate of extracts of wild-type cells. However, addition of phosphoribosyl pyrophosphate stimulated the conversion of adenosine to nucleotides 40-fold. Similarly, intact adenosine kinase-deficient cells failed to phosphorylate the adenosine analogs, but still converted adenosine to nucleotides at 5-10% the rate observed with wild-type cells. Phosphorylation of adenosine and tubercidin in wild-type cells was inhibited by substrate at concentration above 5-10 microM. In contrast, the rate of conversion of adenosine to nucleotides by adenosine kinase-deficient cells increased linearly up to a concentration of 400 microM adenosine, with the consequence that, at this concentration, these cells took up adenosine almost as rapidly as wild-type cells. Adenosine uptake by these kinase-deficient cells was inhibited by adenine and 5'-deoxyadenosine, and was largely abolished in mutants devoid also of adenine phosphoribosyltransferase. We conclude that adenosine is converted to nucleotides in adenosine kinase-deficient cells via adenine. Indirect evidence implicates 5'-methylthioadenosine phosphorylase as the enzyme responsible for the degradation of adenosine to adenine.
 ...
PMID:Adenosine metabolism in wild-type and enzyme-deficient variants of Chinese hamster ovary and Novikoff rat hepatoma cells. 630 18

The exact source of de novo adenine produced by mammalian cells remain poorly understood, and this prompted the present study. Using a human lymphoblastoid cell line (WI-L2) deficient in adenine phosphoribosyltransferase (EC 2.4.2.7), we have quantitated the rate of adenine synthesis and the relative importance of the phosphorolysis of 5'-methylthioadenosine versus adenosine or 2'-deoxyadenosine in adenine generation. Dividing adenine phosphoribosyltransferase-deficient WI-L2 cells produced adenine at a rate of 0.27 nmol/mg protein/h. This represented approximately 10% of the rate of hypoxanthine production by WI-L2 cells deficient in hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) but was equivalent to the rate of 5'-methylthioadenosine synthesis by human lymphoblastoid CCRF-CEM deficient in 5'-methylthioadenosine, phosphorylase (5'-methylthioadenosine: orthophosphate methylthioribosyltransferase). Up to 97% of adenine, but not hypoxanthine, synthesis was inhibited dose-dependently by the S-adenosylmethionine decarboxylase-inhibitor methylglyoxal bis(guanylhydrazone) and also by spermidine and spermine, but was enhanced by putrescine. The addition of 2-fluoroadenine, a potent competitive inhibitor of methylthioadenosine phosphorylase (Ki = 0.43 microM) to adenine phosphoribosyl-transferase-deficient cells resulted in a progressive accumulation of 5'-methylthioadenosine in the culture medium, and up to an 85% decrease in adenine production at non-toxic concentrations. These results show that de novo adenine synthesis by dividing human cells is considerable, and that 85-97% derives from the cleavage of 5'-methylthioadenosine and hence from polyamine synthesis.
 ...
PMID:Dependence of adenine production upon polyamine synthesis in cultured human lymphoblasts. 679 2

EHEB cells, a continuous cell line derived from a patient with B cell chronic lymphocytic leukemia (B-CLL), synthesized, when incubated with tritiated 2-chloro-2'-deoxyadenosine (CdA), labeled mono-, di-, and triphosphate ribonucleosides at a much higher rate than CdA deoxyribonucleotides. Further analysis revealed that these ribonucleotides were formed from labeled 2-chloroadenine (CAde), which contaminated commercial tritiated CdA at a proportion of 2-3%. Since CAde is the major catabolite of CdA measured in plasma after oral or intravenous administration of CdA to patients, its metabolism and in particular its potential cytotoxicity were investigated both in EHEB cells and in B-CLL lymphocytes. Phosphorylation of CAde was inhibited by adenine, indicating that its initial metabolism most probably proceeds via adenine phosphoribosyltransferase (EC 2.4.2.7). In both cell types, chloro-ATP was the major metabolite formed from CAde and its concentration increased proportionally at least up to 50 microM CAde. At high concentration, CAde metabolism was accompanied by a decrease in intracellular ATP. Cytotoxicity of CAde, evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, showed an IC(50) of 16 microM in EHEB cells and 5 microM in B-CLL lymphocytes. At cytotoxic concentrations, apopain/caspase-3 activation and high molecular weight DNA fragmentation were observed, indicating that CAde cytotoxicity results from induction of apoptosis. However, since CAde cytotoxicity requires higher concentrations than CdA, it probably does not play a role in the therapeutic effect of CdA in the treatment of hematologic malignancies.
 ...
PMID:Metabolism and cytotoxic effects of 2-chloroadenine, the major catabolite of 2-chloro-2'-deoxyadenosine. 1073 24