Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
 2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rates of purine synthesis de novo, as measured by the incorporation of [14C]formate into newly synthesized purines, have been determined in cultured human fibroblasts derived from normal individuals and from patients deficient in adenosine deaminase, purine nucleoside phosphorylase, or hypoxanthine phosphoribosyltransferase, three consecutive enzymes of the purine salvage pathway. All four types of cell lines are capable of incorporating [14C]formate into purines at approximately the same rate when the assays are conducted in purine-free medium. The purine overproduction that is characteristic of a deficiency in either the transferase or the phosphorylase and that results from a block in purine reutilization can be demonstrated by the resistance of [14C]formate incorporation into purines to inhibition by hypoxanthine in the case of hypoxanthine phosphoribosyltransferase-deficient fibroblasts and by resistance to inhibition by inosine in the case of purine nucleoside phosphorylase-deficient fibroblasts.
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PMID:Purine metabolism in cultured human fibroblasts derived from patients deficient in hypoxanthine phosphoribosyltransferase, purine nucleoside phosphorylase, or adenosine deaminase. 9 41

Metabolic studies in HEp-2/MP,MIR cells (an adenosine kinase, hypoxanthine phosphoribosyltransferase negative mutant) indicated the presence of adenosine phosphorylase activity. This activity, unknown in established mammalian cell lines, resulted in the glycosidic cleavage of both adenosine and the antiviral drug arabinosyladenine. The activity was observed readily in the presence or absence of the adenosine deaminase inhibitor conformycin. Isopycnic separation of [3H] thymidine-labeled DNA species in CsCl density gradients resulted in the appearance of two distinct peaks. The heavier peak coincided with [14C]thymidine-labeled marker DNA of human origin, whereas the lighter peak was within the range associated with mycoplasmal DNA. Testing by commercial laboratories confirmed the presence of mycoplasma in HEp-2/MP,MIR cells. The contaminant was identified as Mycoplasma hyorhinis, a porcine mycoplasma. Following gamma-irradiation (3000 rads) to block cellular mitosis, the mucoplasma-contaminated HEp-2/MP,MIR cells were cocultivated with mycoplasma-free wild-type HEp-2 cells which did not exhibit adenosine phosphorylase activity. Following serial cocultivation in a medium designed to favor the survival of the wild-type cells, adenosine phosphorylase activity was found in the previously uninfected cells. Studies of this nature emphasize the need for investigators to carefully monitor their cell lines for mycoplasma.
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PMID:Adenosine phosphorylase activity in a mutant HEp-2 cell line contaminated with Mycoplasm hyorhinis. 40 62

Genetic defects in purine metabolism are associated with severe immunodeficiency. Adenosine deaminase deficiency impairs the function of both B- and T-lymphocytes whereas in purine nucleoside (inosine) phosphorylase deficiency there is more severe impairment of T-lymphocyte functions than of B-lymphocyte functions. The relative unimportance of the salvage pathway catalysed by hypoxanthine-guanine phosphoribosyltransferase is shown by the normal responses of T-lymphocytes from patients with the Lesch-Nyhan syndrome to antigenic and mitogenic stimulation. A mild deficiency of B-lymphocyte function is found in these patients. Agents inhibiting the de novo pathway of purine synthesis, including azaserine, 6-mercaptopurine and azathioprine in low doses, block the responses of normal human lymphocytes to mitogenic stimulation. These observations emphasize the importance of the de novo pathway of purine synthesis in lymphocyte responses to antigenic and mitogenic stimulation. There is considerable heterogeneity in the amount of labelled uridine incorporated into human and rat lymphocytes. This does not appear to reflect only a difference between T- and B-lymphocytes
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PMID:The role of de novo purine synthesis in lymphocyte transformation. 41 50

Cell extracts of Acholeplasma laidlawii B-PG9, Acholeplasma morum S2, Mycoplasma capricolum 14, and Mycoplasma gallisepticum S6 were examined for 37 cytoplasmic enzyme activities involved in the salvage and biosynthesis of purines. All of these organisms had adenine phosphoribosyltransferase activity (EC 2.4.2.7) and hypoxanthine phosphoribosyltransferase activity (EC 2.4.2.8). All of these organisms had purine-nucleoside phosphorylase activity (EC 2.4.2.1) in the synthetic direction using ribose-1-phosphate (R-1-P) or deoxyribose-1-phosphate (dR-1-P); this activity generated ribonucleosides or deoxyribonucleosides, respectively. The pyrimidine nucleobase uracil could also be ribosylated by using either R-1-P or dR-1-P as a donor. The synthesis of deoxyribonucleosides from nucleobases and dR-1-P has been reported from only one other procaryote, Escherichia coli (L. A. Mason and J. O. Lampen, J. Biol. Chem. 193:539-547, 1951). The reverse of this phosphorylase reaction is more widely known, and we found such activity in all mollicutes studied. Some Acholeplasma species but not the Mycoplasma species can phosphorylate deoxyribonucleosides to deoxyribomononucleotides by a PPi-dependent deoxyribonucleoside kinase activity, which was first reported in this group for the ribose analogs (V. V. Tryon and J. D. Pollack, Int. J. Syst. Bacteriol. 35:497-501, 1985). This is the first report of PPi-dependent purine deoxyribonucleoside kinase activity. An ATP-dependent purine deoxyribonucleoside kinase activity is known only in salmon milt extracts (H. L. A. Tarr, Can. J. Biochem. 42:1535-1545, 1964). Deoxyribomononucleotidase activity was also found in cytoplasmic extracts of these mollicutes. This is the first report of deoxyribomononucleotidase activity.
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PMID:Synthesis of deoxyribomononucleotides in Mollicutes: dependence on deoxyribose-1-phosphate and PPi. 303 46

Bacillus subtilis mutants defective in purine metabolism have been isolated by selecting for resistance to purine analogs. Mutants resistant to 2-fluoroadenine were found to be defective in adenine phosphoribosyltransferase (apt) activity and slightly impaired in adenine uptake. By making use of apt mutants and mutants defective in adenosine phosphorylase activity, it was shown that adenine deamination is an essential step in the conversion of both adenine and adenosine to guanine nucleotides. Mutants resistant to 8-azaguanine, pbuG mutants, appeared to be defective in hypoxanthine and guanine transport and normal in hypoxanthine-guanine phosphoribosyltransferase activity. Purine auxotrophic pbuG mutants grew in a concentration-dependent way on hypoxanthine, while normal growth was observed on inosine as the purine source. Inosine was taken up by a different transport system and utilized after conversion to hypoxanthine. Two mutants resistant to 8-azaxanthine were isolated: one was defective in xanthine phosphoribosyltransferase (xpt) activity and xanthine transport, and another had reduced GMP synthetase activity. The results obtained with the various mutants provide evidence for the existence of specific purine base transport systems. The genetic lesions causing the mutant phenotypes, apt, pbuG, and xpt, have been located on the B. subtilis linkage map at 243, 55, and 198 degrees, respectively.
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PMID:Genetic and physiological characterization of Bacillus subtilis mutants resistant to purine analogs. 311 Jan 31

Long-term bovine lymphocyte cultures were initiated by stimulation with alloantigens and maintained in continuous culture using medium containing recombinant human interleukin-2 (rh IL-2). The development of specific and lectin-dependent killing was monitored following primary alloantigen challenge. Cytolytic activity was barely detectable after 7 days of culture, but gradually increased with peak activity occurring after 21 days of culture. A panel of monoclonal antibodies (MoAb) was used to determine whether a shift in the antigen phenotype of the cell population occurred during culture. The primary cell type that grew in culture was of the T-cell lineage with minimal or no expression of class II antigens. The activities of adenosine deaminase (ADA), purine nucleotide phosphorylase (PNP), adenosine kinase (AK), deoxyadenosine kinase (dAK), deoxycytidine kinase (dCK), 5'-nucleotidase (5'-N), AMP deaminase, hypoxanthine-guanine phosphoribosyl transferase (HGPRT or HPRT), and adenine phosphoribosyl transferase (APRT) were measured by microassay in resting peripheral blood lymphocytes (PBL) and in cells from long-term cultures. Large increases in the activities of PNP and HPRT with a decrease in the activity of ADA were observed. The data show that long-term cultures of lymphocytes can be readily generated, and that sequential changes in antigenic phenotype and function can be monitored and correlated with quantitative changes in enzyme activity.
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PMID:Development and maintenance of bovine cytotoxic lymphocytes with recombinant human interleukin-2. 348 20

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.
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PMID:Dependence of adenine production upon polyamine synthesis in cultured human lymphoblasts. 679 2