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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The regulation of adenosine phosphorylation by adenosine analogs was studied using highly purified human placental adenosine kinase [ATP: adenosine 5'-phosphotransferase (EC 2.7.1.20)]. Our observations lead us to classify the analogs into three groups as follows: type I, 5'-N-ethylcarboxamidoadenosine and 5'-methylthioadenosine; type II, N6-cyclohexyladenosine, N6-L-phenylisopropyladenosine, and 2-chloroadenosine; and type III, 6-methylmercaptopurine riboside. Type I compounds are inhibitors of adenosine kinase at 0.5 microM adenosine with IC50 values of 25 microM for 5'-N-ethylcarboxamidoadenosine and 250 microM for 5'-methylthioadenosine. These compounds stimulate adenosine kinase at 5.0 microM adenosine up to a maximum of 30 to 50% above basal velocity. They are not substrates for adenosine kinase. Type II compounds are inhibitors of adenosine kinase at 0.5 microM adenosine with an IC50 of 220 microM for N6-cyclohexyladenosine and 200 microM for N6-L-phenylisopropyladenosine. These analogs also stimulate adenosine kinase at 5.0 microM adenosine. 2-Chloroadenosine, N6-cyclohexyladenosine, and N6-L-phenylisopropyladenosine are phosphorylated by adenosine kinase with apparent Km values of 1,330, and 205 microM, respectively. 6-Methylmercaptopurine riboside (type III) inhibited enzyme activity with an IC50 of 10 microM at 0.5 microM adenosine and 215 microM at 5 microM adenosine and is a substrate for adenosine kinase. These data are consistent with the following: (a) 2-chloroadenosine, N6-cyclohexyladenosine, and N6-L-phenylisopropyladenosine may not be good adenosine receptor agonists in vivo because they are phosphorylated into active derivatives by adenosine kinase; (b) 5'-N-ethylcarboxamidoadenosine and 5'-methylthioadenosine are superior candidates for adenosine receptor agonists in vivo because they are not phosphorylated; (c) 5'-N-ethylcarboxamidoadenosine, 5'-cyclohexyladenosine, N6-L-phenylisopropyladenosine, and 2-chloroadenosine may interact with adenosine kinase at two sites on the enzyme, a catalytic site and a regulatory site; and (d) 6-methylmercaptopurine riboside may interact with the enzyme at the catalytic site only.
Mol Pharmacol 1988 Oct
PMID:Regulation of adenosine kinase by adenosine analogs. 284 49

The enzymes that catalyse the salvage of purines in Entamoeba histolytica trophozoites have been surveyed. Adenine deaminase (EC 3.5.4.2), adenosine deaminase (EC 3.5.4.4), guanine deaminase (EC 3.5.4.3), adenine phosphoribosyltransferase (PRTase) (EC 2.4.2.7), xanthine PRTase (EC 2.4.2.22) and hypoxanthine PRTase (EC 2.4.2.8) were all detected in cell homogenates but only at low activities, whereas AMP deaminase (EC 3.5.4.6) and guanine PRTase (EC 2.4.2.8) were not found. Phosphorylases (EC 2.4.2.1) active in both anabolic and catabolic directions were present and all nucleosides tested were phosphorylated by kinases (EC 2.7.1.15, EC 2.7.1.20, EC 2.7.1.73). 3'-Nucleotidase (EC 3.1.3.6) and 5'-nucleotidase (EC 3.1.3.5) were found, the former being mainly particulate. Nucleotide interconversion enzymes (adenylosuccinate lyase, EC 4.3.2.2; adenylosuccinate synthetase, EC 6.3.4.4; IMP dehydrogenase, EC 1.2.1.14; GMP synthetase, EC 6.3.5.2 and GMP reductase, EC 1.6.6.8) were not detected. The results suggest that in E. histolytica the main route of nucleotide synthesis is from the individual bases through the actions of phosphorylases and kinases.
Mol Biochem Parasitol 1986 Apr
PMID:Purine-metabolising enzymes in Entamoeba histolytica. 287 91

We have determined the regional locations on mouse chromosome 14 of the genes for mouse adenosine kinase (ADK), nucleoside phosphorylase-1 (NP-1), and esterase-10 (ES-10) by analysis of rearranged mouse chromosomes in gamma-irradiated Chinese hamster X mouse hybrid cell lines. Irradiated clones were screened for expression of the murine forms of these enzymes; segregant clones that expressed only one or two of the three markers were karyotyped. The patterns of enzyme expression in these segregants were correlated with the presence of rearranged chromosomes. The Adk gene was localized to bands A2 to B, Np-1 to bands B to C1, and Es-10 to bands D2 to E2.
Somat Cell Mol Genet 1985 Mar
PMID:Cytological localization of adenosine kinase, nucleoside phosphorylase-1, and esterase-10 genes on mouse chromosome 14. 298 88

In cell cultures treated with the carbocyclic analog of adenosine (C-Ado, (+/-)-aristeromycin), the utilization of hypoxanthine and guanine has been observed to be blocked. In an attempt to define the mechanism of this inhibition, we have reexamined the metabolism of C-Ado and its effects on the metabolism of guanine and hypoxanthine. In cultures of L1210 cells, C-Ado at a concentration of 25 microM inhibited the utilization of hypoxanthine and guanine for nucleotide synthesis by more than 90% but produced little or no inhibition of the utilization of these bases in cultures of L1210/MeMPR cells which lack adenosine kinase and cannot phosphorylate C-Ado. In cultures of mammalian cells (L1210, HEp-2, and colon-26 cells), C-Ado was converted to the triphosphate (as previously observed) and also to the triphosphate of the carbocyclic analog of guanosine. The presence of coformycin in the medium at a concentration sufficient to inhibit AMP deaminase almost completely prevented the formation of carbocyclic GTP; thus, the deamination of C-Ado monophosphate is essential for the formation of phosphates of carbocyclic guanosine. Since hypoxanthine (guanine) phosphoribosyltransferase is known to be subject to end product inhibition, it was considered likely that phosphates of carbocyclic guanosine or carbocyclic inosine, present in C-Ado-treated cells, were responsible for inhibition of utilization of hypoxanthine and guanine. The 5'-phosphates of the carbocyclic analogs of inosine and guanosine were synthesized and found to be effective inhibitors of the phosphoribosyltransferase. Carbocyclic GMP was a better inhibitor than carbocyclic IMP and was also superior to GMP and IMP; the concentration of C-GMP that produced a 50% inhibition of GMP formation was approximately 1 microM. It is probable that the presence of phosphates of carbocyclic guanosine accounts for the inhibition of utilization of hypoxanthine and guanine in C-Ado-treated cells.
Mol Pharmacol 1985 Jun
PMID:Inhibition of utilization of hypoxanthine and guanine in cells treated with the carbocyclic analog of adenosine. Phosphates of carbocyclic nucleoside analogs as inhibitors of hypoxanthine (guanine) phosphoribosyltransferase. 298 61

Stable mutants which are approximately five- and eightfold resistant to an inosine analog, formycin B (Fomr) have been selected in a single-step from Chinese hamster ovary cells at a frequency of approximately 10(-6). Cross-resistance studies with these mutants show that the Fomr mutants exhibit increased resistance to all adenosine analogs (N-and C-nucleosides) examined and, in accordance with their cross-resistance pattern, the mutants exhibited decreased cellular uptake and phosphorylation of formycin B and various adenosine analogs. In cell hybrids formed with sensitive cells, the drug-resistant phenotype of these mutants behaved recessively. However, unlike mutants resistant to adenosine analogs that have been obtained previously, which contain no measurable activity of adenosine kinase (AK) in cell extracts, the two Fomr mutants studied contained about 60 and 110% of the enzyme activity (compared to the parental cells) in their cell extracts. Biochemical studies with AK from the mutant cells show that in comparison to the wild-type enzyme, the mutant enzymes required much higher concentrations of the adenosine analog N7-(delta 2-isopentenyl) formycin A for similar inhibition of [3H]adenosine phosphorylation. These results indicate that AK from the Fomr mutants has lower affinity for phosphorylation of adenosine analogs in comparison to the enzyme from the parental cells. The genetic lesion in the Fomr mutants may thus be directly affecting the structural gene for AK.
Somat Cell Mol Genet 1986 Jan
PMID:Novel mutants of CHO cells resistant to adenosine analogs and containing biochemically altered form of adenosine kinase in cell extracts. 300 29

Activities of several adenosine metabolizing enzymes were examined in capillary preparations isolated from rabbit ventricle. Vmax and Km values for 5'-nucleotidase were 2.3 nmol/min/mg and 10 microM, respectively. For adenosine deaminase the corresponding values were 7.8 nmol/min/mg and 32 microM. S-adenosyl-homocysteine hydrolase, which forms adenosine by the hydrolysis of S-adenosylhomo-cysteine, was also present (Vmax, 0.07 nmol/min/mg; Km, 0.81 microM), as were adenosine kinase (Vmax, 0.2 nmol/min/mg; Km, 0.52 microM) and purine nucleoside phosphorylase (Vmax, 13.8 nmol/min/mg; Km, 96 microM). These enzymes were also present in microvessels (capillaries and arterioles) purified from rabbit brain. Activities of several enzymes, especially 5'-nucleotidase and adenosine deaminase, were much lower in myocytes isolated from rabbit ventricle. The study provides evidence that endothelial cells of the microvasculature from heart and brain are capable of activity forming and degrading adenosine. It is possible that adenosine formed by these cells may contribute to the local regulation of blood flow.
J Mol Cell Cardiol 1986 Jan
PMID:Adenosine metabolism in microvessels from heart and brain. 300 95

Adenosine kinase (AK) from CHO cells has been purified to homogeneity and specific antibodies to it have been raised in rabbits. Using this antibody, the presence of a specific cross-reacting protein (CRP) in cell extracts of different classes of mutants resistant to purine nucleoside analogs which are affected in AK has been investigated by the immunoblotting technique. Results of our studies show that 31 of the 32 independently selected class A AK- mutants (obtained at high frequency in presence of adenosine analogs toyocamycin, tubercidin, 6-methylmercaptopurine riboside, or pyrazofurin and containing no measurable activity of AK in cell extracts) contained similar amounts of a specific CRP as seen in the parental AK+ cells. The CRP in the parental and different mutant cell lines has the same relative molecular mass as purified AK. Similar results were obtained with two mutants each of the class B and C type (selected in presence of C-nucleosides formycin A and formycin B), which are also affected in AK but show novel properties. The presence of equivalent amounts of the CRP in the vast majority of the class A mutants strongly indicates that the high frequency of those mutants in CHO cells is not a result of an epigenetic or deletion type of event, but that such mutants may contain missense types of mutations at a presumed "mutational hot spot" within the structural gene for adenosine kinase.
Somat Cell Mol Genet 1986 May
PMID:Immunological studies with different classes of mutants affected at the adenosine kinase locus in CHO cells. 301 99

AMP deaminase, the activity that catalyzes the deamination of AMP to form IMP and NH3 has been measured in Dictyostelium discoideum. A new procedure to assay the activity of this enzyme was developed using formycin 5'-monophosphate, a fluorescent analog of AMP as the substrate, and ion-paired reverse phase HPLC to separate the reactants and products. Quantitation of the formycin containing compounds was accomplished at 290 nm. At this wavelength adenosine containing compounds were not detected and activity could be monitored in the presence of its activator ATP. The AMP deaminase activity in vegetative cells was 7.4 nmols/min/mg proteins while the activity in cells measured at 2 and 6 hrs after starvation-induced growth-arrest was 376 nmols/min/mg protein...a 51-fold increase. When vegetative cells were treated with hadacidin, a drug that restricts de novo AMP synthesis and pinocytosis, the activity of the AMP deaminase was 511 nmols/min/mg protein...a 70-fold increase compared to that in untreated vegetative cells. Smaller increases were noted following the inhibition of growth with the drugs cerulenin and vinblastine, as well as after the inhibition of de novo GMP synthesis with the drug mycophenolic acid or the partial inhibition of de novo AMP synthesis with analogs of hadacidin, N-hydroxyglycine and N-formylglycine. In addition, when the activity of two other enzymes involved in purine metabolism, namely adenosine kinase and hypoxanthine-guanine phosphoribosyl transferase, was measured in vegetative cells, and the activity of both compared to that measured in starvation and hadacidin induced growth-arrested cells, showed no significant changes.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Biochem 1986 Jun
PMID:AMP deaminase in Dictyostelium discoideum: increase in activity following nutrient deprivation induced by starvation or hadacidin. 301 11

The effect of pyrazofurin, an inhibitor of UMP synthesis, on Plasmodium falciparum growth in vitro has been studied. ID50 values (concentration of compound causing 50% inhibition of [3H]hypoxanthine incorporation) for the FCQ-27, FCI-1 and K-1 (chloroquine-resistant) isolates were 10 +/- 8.7, 6.4 +/- 5.3 and 6.3 +/- 0.5 microM, respectively. Comparative ID50 values for chloroquine were 13.5 +/- 4.2, 22.8 +/- 7.6 and 343 +/- 114 microM, respectively. Over the 48-h intraerythrocytic cycle of tightly synchronized parasites, pyrazofurin both reduced the parasitemia and retarded the maturation of trophozoites and schizonts. Addition of uracil or uridine to the in vitro culture did not decrease the anti-parasitic activity of pyrazofurin. Chloroquine reduced the parasitemia, but did not retard development of the remaining viable parasites. Pyrazofurin (20 microM) caused a 50% inhibition of parasite orotate phosphoribosyltransferase (E.C. 2.4.2.10) and, in the presence of adenosine kinase and ATP, a 73% inhibition of orotidine-5'-phosphate decarboxylase (E.C. 4.1.1.23).
Mol Biochem Parasitol 1986 Jan
PMID:In vitro inhibition of Plasmodium falciparum by pyrazofurin, an inhibitor of pyrimidine biosynthesis de novo. 351 74

Three different phenotypes have been characterized in HeLa cells that have been selected for resistance to pyrazofurin, a potent inhibitor of the de novo pyrimidine biosynthetic enzyme UMP synthase. All of the resistant cell lines had a coordinate increase in UMP synthase activity, UMP synthase-specific mRNA, and UMP synthase gene sequences. In one of the resistant cell lines, the amplification of the UMP synthase gene is associated with a stable phenotype. There is no decrease in UMP synthase gene copy number or UMP synthase activity when these cells are grown for over six months in the absence of pyrazofurin. Another resistant cell line that has a higher level of gene amplification when grown in the presence of pyrazofurin loses its elevated UMP synthase activity and amplified DNA sequences with growth in the absence of the drug. A third cell line that possessed a moderate level of UMP synthase gene amplification is tenfold more resistant to pyrazofurin than the cell line with the highest level of amplification. The extraordinary level of resistance is due to a decreased level of activity for the enzyme adenosine kinase that is required for the conversion of pyrazofurin to its inhibitory monophosphate form.
Somat Cell Mol Genet 1985 Jul
PMID:Characterization of pyrazofurin-resistant HeLa cells with amplification of UMP synthase gene. 386 Sep 66


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