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:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The adenylate kinase 1 (AK1), adenylate kinase3 (AK3), and aconitaseS (ACONS) genes have been assigned to chromosome 9 in man by employing an X/9 translocation segregating in man-mouse somatic cell hybrids. Segregation was controlled by taking advantage of the HAT/8-azaguanine selection-counterselection strategy directed at the X-linked HPRT locus. Assignment of AK1 to chromosome 9 has suggested the assignment of the ABO blood-group locus and the nail-patella (Np) locus to 9, since both loci are linked to AK1 by family studies.
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PMID:Mapping AK1, ACONs, and AK3 to chromosome 9 in man employing and X/9 translocation and somatic cell hybrids. 19 13

Early embryonic development in Xenopus laevis is programmed in part by maternally derived mRNAs, many of which are translated at the completion of meiosis (oocyte maturation). Polysomal recruitment of at least one of these mRNAs, G10, is regulated by cytoplasmic poly(A) elongation which, in turn, is dependent upon the cytoplasmic polyadenylation element (CPE) UUUUUUAUAAAG and the hexanucleotide AAUAAA (L. L. McGrew, E. Dworkin-Rastl, M. B. Dworkin, and J. D. Richter, Genes Dev. 3:803-815, 1989). We have investigated whether sequences similar to the G10 RNA CPE that are present in other RNAs could also be responsible for maturation-specific polyadenylation. B4 RNA, which encodes a histone H1-like protein, requires a CPE of the sequence UUUUUAAU as well as the polyadenylation hexanucleotide. The 3' untranslated regions of Xenopus c-mos RNA and mouse HPRT RNA also contain U-rich CPEs since they confer maturation-specific polyadenylation when fused to Xenopus B-globin RNA. Polyadenylation of B4 RNA, which occurs very early during maturation, is limited to 150 residues, and it is this number that is required for polysomal recruitment. To investigate the possible diversity of factors and/or affinities that might control polyadenylation, egg extracts that faithfully adenylate exogenously added RNA were used in competition experiments. At least one factor is shared by B4 and G10 RNAs, although it has a much greater affinity for B4 RNA. Additional experiments demonstrate that an intact CPE and hexanucleotide are both required to compete for the polyadenylation apparatus. Gel mobility shift assays show that two polyadenylation complexes are formed on B4 RNA. Optimal complex formation requires an intact CPE and hexanucleotide but not ongoing adenylation. These data, plus additional RNA competition studies, suggest that stable complex formation is enhanced by an interaction of the trans-acting factors that bind the CPE and polyadenylation hexanucleotide.
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PMID:Maturation-specific polyadenylation and translational control: diversity of cytoplasmic polyadenylation elements, influence of poly(A) tail size, and formation of stable polyadenylation complexes. 170 Feb 72

The proliferative effect of insulin on de novo purine synthesis and on the expression of various enzymes of purine metabolism were studied in primary cultured rat hepatocytes. Insulin greater than 1.5 x 10(-8) M increased DNA and de novo purine synthesis to 260-390 and 270-420%, respectively, 24 and 8 h after the administration. Insulin at 1.5 x 10(-7) M increased the specific activity of amidophosphoribosyltransferase (ATase) to 154-180%, hypoxanthine-guanine phosphoribosyltransferase to 129%, and adenine phosphoribosyltransferase (APRT) to 205%, in contrast to unchanged xanthine dehydrogenase at 80%. Enzyme induction was supported by the results of kinetic analysis and the inhibition of the insulin-induced increase in enzyme activities by protein synthesis inhibitors. Insulin increased ATP to 127% and decreased AMP, ADP, 5'-guanylic acid (GMP), and guanosine 5'-diphosphate (GDP), respectively, to 73, 69, 73, and 69%. Insulin increased adenylate energy charge from 0.83 to 0.90 without changing total feedback inhibitory potential on ATase. No obvious increase of 5-phosphoribosyl-1-pyrophosphate supply was suggested, although its apparent availability for purine ribonucleotide synthesis was increased to 208-245%, reflecting mainly induced APRT activity to 205%. It is concluded that hepatocyte proliferation by insulin, as evidenced by purine metabolism, is mediated by the selective gene activation of anabolic enzymes and increased ATP as the basis to activate multiple metabolic pathways without remarkable changes of substrate availability or feedback inhibition.
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PMID:Increased de novo purine synthesis by insulin through selective enzyme induction in primary cultured rat hepatocytes. 218 59

Using radiochemical methods, we determined the activities of various enzymes of purine and pyrimidine metabolism in homogenates of human skeletal muscle and of cultured human muscle cells. Results show a large discrepancy between the enzyme activities in muscle and cultured cells. With regard to purine metabolism, adenylate (AMP) deaminase activity was only 1-3% in cultured cells compared to that in muscle, whereas the activity of adenosine deaminase, purine-nucleoside phosphorylase, adenosine kinase, adenine phosphoribosyltransferase and hypoxanthine phosphoribosyltransferase was 7-15-fold higher in the cultured cells. The enzymes of pyrimidine metabolism, orotate phosphoribosyltransferase, orotidine 5'-monophosphate decarboxylase and uridine kinase showed activity of 100-200-fold higher in cultured cells than in adult muscle. The differences in enzyme activity are probably related to the low differentiation stage and the absence of contractile activity in the cultured muscle cells. Care must be taken when using these cells as a model for studying purine and pyrimidine metabolism of adult myofibers.
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PMID:Purine and pyrimidine metabolism in human muscle and cultured muscle cells. 283 95

The specific activities of the three enzymes of the inosinate branchpoint are independently regulated when lymphoblasts are grown under various tissue culture conditions. In comparison to rapidly dividing cells, lymphoblasts at high cell density with no cellular division have decreased activity of the enzymes which commit inosinate to adenylate or guanylate, while cytoplasmic 5'-nucleotidase is relatively preserved. A linear relationship between inosinate dehydrogenase activity and growth rate (r = 0.92) exists in lymphoblasts with slowed growth rates. In contrast, in dividing cells adenylosuccinate synthetase and 5'-nucleotidase do not vary with growth rate. Adenylosuccinate synthetase and inosinate dehydrogenase activities appear to be related to the presence or rate of cellular division, as opposed to the presence or degree of neoplastic transformation. Lymphoblast lines with alterations of specific purine metabolic enzymes have characteristic alteration of the inosinate utilizing enzymes. Deficiencies of purine nucleoside phosphorylase or hypoxanthine phosphoribosyltransferase, abnormalities which render the cell unable to salvage purine effectively, are associated with depressed inosinate dehydrogenase activity. Insertion of the hypoxanthine phosphoribosyltransferase gene into hypoxanthine phosphoribosyltransferase-deficient cells normalizes inosinate dehydrogenase activity, while a hypoxanthine phosphoribosyltransferase-deficient mutant selected from a hypoxanthine phosphoribosyltransferase-containing line has depressed inosinate dehydrogenase activity. In contrast, overactivity of phosphoribosylpyrophosphate synthetase, with enhanced excretion of purines due to excessive production, is associated with elevated inosinate dehydrogenase activity. Inosinate dehydrogenase appears to be regulated according to the availability of purine nucleotides. Patients who overproduce uric acid and potentially have undescribed purine metabolic defects are now being screened for abnormalities in the inosinate branchpoint enzymes.
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PMID:Alterations of inosinate branchpoint enzymes in cultured human lymphoblasts. 286 60

WI-L2 B lymphoblasts deficient in hypoxanthine-guanine phosphoribosyltransferase (HGPRT) excreted amounts of hypoxanthine two to three times larger than CEM T lymphoblasts deficient in HGPRT, despite similar growth rates. ATP consumption occurred at a higher rate in WI-L2 cells than in CEM cells when cultivated in a glucose-free buffer, because of higher RNA synthesis in WI-L2 cells. The introduction of actinomycin D and azaserine resulted in lower hypoxanthine excretion in WI-L2 cells than in CEM cells, not in parallel with changes of the adenylate pool size. When the energy charge was high, de novo purine synthesis was a major determinant for purine excretion. The adenylate pool ratio (AMP/ATP) change caused by the introduction of oligomycin was greater during ATP depletion and recovery in WI-L2 cells than in CEM cells. WI-L2 cells were observed to have AMP deaminase activity three to four times higher than CEM cells. The major component of AMP deaminase in these cells was liver type. The higher rate of RNA synthesis caused greater changes of (AMP/ATP) and required higher AMP deaminase activity for recovery. When the energy charge was low, AMP deaminase was a major determinant for purine excretion.
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PMID:Major determinants of purine excretion from human lymphoblasts. 343 82

Hypoxanthine was converted primarily to uric acid by thyroid tissue slices and homogenates with little inosine 5'-monophosphate formation while adenine was essentially all salvaged to adenosine 5'-monophosphate by similar tissue preparations. The ratio of hypoxanthine/guanine phosphoribosyltransferase activity to adenine phosphoribosyltransferase activity was 0.15 in the thyroid homogenates.
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PMID:Hypoxanthine and adenine metabolism in bovine thyroid tissue. 375 91

Adenosine kinase, adenosine deaminase, hypoxanthine phosphoribosyltransferase, inosine-nucleoside phosphorylase, 5'-AMP deaminase and 5'-IMP nucleotidase were identified in cell-free extracts of duckling erythrocytes; no evidence for 5'-AMP nucleotidase and xanthine oxidase activity was found. The Km values for the duckling red cell enzymes were similar to those reported for human erythrocytes. Plasmodium lophurae extracts demonstrated similar enzyme activities except for 5'-AMP deaminase and 5'-IMP nucleotidase which were absent. It is proposed that during infection erythrocytic AMP is catabolized to IMP, inosine and hypoxanthine; the hypoxanthine is taken up by the plasmodium, utilized to form IMP, and this in turn is converted into adenine and guanine nucleotides.
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PMID:Purine metabolizing enzymes of Plasmodium lophurae and its host cell, the duckling (Anas domesticus) erythrocyte. 678 22

Many enzymes are involved in the biosynthesis, interconversion, and degradation of purine compounds. The exact function of these enzymes is still unknown, but they seem to play important roles other than in purine metabolism. To elucidate their functional roles, it is imperative to clarify their tissue distribution at the cellular or subcellular level. The present review summarizes the currently available information about their histochemical localization and proposed functions. In general, 5'-nucleotidase has been considered as a marker enzyme for the plasma membrane, and is considered to be a key enzyme in the generation of adenosine, a potential vasodilator. However, from its wide range of localization in tissues it is also considered to be related to the membrane movement of cells in the transitional epithelium, cellular motile response, transport process, cellular growth, synthesis of fibrous protein and calcification, lymphocyte activation, neurotransmission, and oxygen sensing mechanism. Adenosine deaminase (ADA) is present in all tissues in mammals. Although the main function of ADA is the development of the immune system in humans, it seems to be associated with the differentiation of epithelial cells and monocytes, neurotransmission, and maintenance of gestation. Purine nucleoside phosphorylase (PNP) is generally considered as a cytosolic enzyme, but recently, mitochondrial PNP, a different protein from cytosolic PNP, was reported. PNP is also widely expressed in human tissues. It is found in most tissues of the body, but the highest activity is in peripheral blood granulocyte and lymphoid tissues. It is also related to the development of T-cell immunity in humans as is ADA. Moreover, its contribution to centriole replication and/or regulation of microtubule assembly has been suggested. Immunohistochemical localization of xanthine oxidase has been reported in various tissues from various animal species. Xanthine oxidase has been suggested to be involved in the pathogenesis of post-ischemic reperfusion tissue injury through the generation of reactive oxygen species, while the extensive tissue localization of xanthine dehydrogenase/oxidase suggests several other roles for this enzyme, including a protective barrier against bacterial infection by producing either superoxide radicals or uric acid. Furthermore, an involvement in cellular proliferation and differentiation has been suggested. Urate oxidase is generally considered a liver-specific enzyme, except for bovines which possess this enzyme in the kidney. Urate oxidase is exclusively located in the peroxisomes of fish, frogs, and rats, but was lost in birds, some reptiles, and primates during evolution. A histochemical demonstration of allantoin-degrading enzymes has not been performed, but these enzymes have been located in peroxisomes by sucrose density gradient centrifugation. AMP deaminase activity is higher in skeletal muscle than in any other tissues. AMP deaminase may be involved in a number of physiological processes, such as the conversion of adenine nucleotide to inosine or guanine nucleotide, stabilizing the adenylate energy charge, and the reaction of the purine nucleotide cycle. There are three distinct isozymes (A, B, C) with different kinetic, physical, and immunological properties. Isozymes A, B, C have been isolated from muscle, liver (kidney), and heart tissue, respectively. In the muscle, AMP deaminase isozymes exist in a different part, suggesting a multiple functional role of this enzyme. High hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity is found in some regions of a normal adult human brain. However, very little is known regarding the histochemical tissue localization of HGPRT. Immunohistochemical localization of its developmental expression suggests that HGPRT may not be essential for purine nucleotide supplement in the segmentation of brain cells, but may play a significant role in the developing hippocampus.
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PMID:Enzymes involved in purine metabolism--a review of histochemical localization and functional implications. 1050 47

To elucidate the biological significance of extracellular adenine compounds, the effects of adenosine (Ado) on cellular levels of adenine compounds, especially adenosine triphosphate (ATP), in PC12 cells were studied. Ado and inosine but not adenosine 5'-monophosphate, adenosine 5'-diphosphate, ATP, guanosine, cytosine, thymidine, and uridine, significantly enhanced cellular ATP levels in PC12 cells in time- and dose-dependent manners. Various P1 receptor agonists of Ado did not enhance the ATP level. In addition, theophylline, an antagonist of P1 receptors, did not inhibit the Ado-evoked ATP enhancement. These results suggest that the Ado receptor is not involved in the augmentation of the cellular ATP level induced by Ado in PC12 cells. The ATP-enhancing effect of Ado was potentiated by dipyridamole, an inhibitor of Ado uptake, or coformycin, an inhibitor of Ado deaminase. The effect of Ado on the ATP level was also observed when PC12 cells were incubated in glucose-free medium. Together these results suggest that enhancement of cellular ATP levels in PC12 cells by extracellular Ado might be acceleration of ATP synthesis through the Ado salvage system using hypoxanthine-guanine phosphoribosyltransferase rather than Ado kinase since 5'-iodotubercidin, an inhibitor of Ado kinase, had no effect on the enhancement elicited by Ado.
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PMID:Enhancement of cellular adenosine triphosphate levels in PC12 cells by extracellular adenosine. 1191 23


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