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Vliet LK, Wilkinson TG, Duval N, Vacano G, Graham C, Zikánová M, Skopova V, Baresova V, Hnízda A, Kmoch S, Patterson D. Molecular characterization of the AdeI mutant of Chinese hamster ovary cells: a cellular model of adenylosuccinate lyase deficiency. Mol Genet Metab 2011; 102:61-8. [PMID: 20884265 PMCID: PMC3065963 DOI: 10.1016/j.ymgme.2010.08.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Revised: 08/30/2010] [Accepted: 08/30/2010] [Indexed: 11/19/2022]
Abstract
Adenylosuccinate lyase (ADSL, E. C. 4.3.2.2) carries out two non-sequential steps in de novo AMP synthesis, the conversion of succinylaminoimidazole carboxamide ribotide (SAICAR) to aminoimidazolecarboxamide ribotide (AICAR) and the conversion of succinyl AMP (AMPS) to AMP. In humans, mutations in ADSL lead to an inborn error of metabolism originally characterized by developmental delay, often with autistic features. There is no effective treatment for ADSL deficiency. Hypotheses regarding the pathogenesis include toxicity of high levels of SAICAR, AMPS, or their metabolites, deficiency of the de novo purine biosynthetic pathway, or lack of a completely functional purine cycle in muscle and brain. One important approach to understand ADSL deficiency is to develop cell culture models that allow investigation of the properties of ADSL mutants and the consequences of ADSL deficiency at the cellular level. We previously reported the isolation and initial characterization of mutants of Chinese hamster ovary (CHO-K1) cells (AdeI) that lack detectable ADSL activity, accumulate SAICAR and AMPS, and require adenine for growth. Here we report the cDNA sequences of ADSL from CHO-K1 and AdeI cells and describe a mutation resulting in an alanine to valine amino acid substitution at position 291 (A291V) in AdeI ADSL. This substitution lies in the "signature sequence" of ADSL, inactivates the enzyme, and validates AdeI as a cellular model of ADSL deficiency.
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Affiliation(s)
- Lydia K. Vliet
- Eleanor Roosevelt Institute and Department of Biological Sciences, University of Denver, 2101 E. Wesley Avenue, Denver, CO, 80208
| | - Terry G. Wilkinson
- Eleanor Roosevelt Institute and Department of Biological Sciences, University of Denver, 2101 E. Wesley Avenue, Denver, CO, 80208
| | - Nathan Duval
- Eleanor Roosevelt Institute and Department of Biological Sciences, University of Denver, 2101 E. Wesley Avenue, Denver, CO, 80208
| | - Guido Vacano
- Eleanor Roosevelt Institute and Department of Biological Sciences, University of Denver, 2101 E. Wesley Avenue, Denver, CO, 80208
| | - Christine Graham
- Eleanor Roosevelt Institute and Department of Biological Sciences, University of Denver, 2101 E. Wesley Avenue, Denver, CO, 80208
| | - Marie Zikánová
- Center for Applied Genomics, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
- Institute of Inherited Metabolic Disorders, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
| | - Vaclava Skopova
- Center for Applied Genomics, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
- Institute of Inherited Metabolic Disorders, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
| | - Veronika Baresova
- Center for Applied Genomics, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
- Institute of Inherited Metabolic Disorders, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
| | - Aleš Hnízda
- Institute of Inherited Metabolic Disorders, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
| | - Stanislav Kmoch
- Center for Applied Genomics, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
- Institute of Inherited Metabolic Disorders, Charles University in Prague, First Faculty of Medicine, Ke Karlovu 2, 128 00 Prague 2, Czech Republic
| | - David Patterson
- Eleanor Roosevelt Institute and Department of Biological Sciences, University of Denver, 2101 E. Wesley Avenue, Denver, CO, 80208
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Van den Berghe G, Van den Bergh F, Vincent MF, Jaeken J. Adenylosuccinate lyase deficiency: an update. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1995; 370:363-6. [PMID: 7660929 DOI: 10.1007/978-1-4615-2584-4_78] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- G Van den Berghe
- Laboratory of Physiological Chemistry, University of Louvain Medical School, Brussels
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Van den Bergh F, Vincent MF, Jaeken J, Van den Berghe G. Residual adenylosuccinase activities in fibroblasts of adenylosuccinase-deficient children: parallel deficiency with adenylosuccinate and succinyl-AICAR in profoundly retarded patients and non-parallel deficiency in a mildly retarded girl. J Inherit Metab Dis 1993; 16:415-24. [PMID: 8412002 DOI: 10.1007/bf00710291] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Adenylosuccinase (ASase) catalyses both the conversion of succinyl-aminoimidazole carboxamide ribotide (succinyl-AICAR) into AICAR and that of adenylosuccinate into AMP in the synthesis of purine nucleotides. Its deficiency results in the accumulation in body fluids of the nucleosides corresponding to both substrates, succinyl-AICAriboside and succinyladenosine. Two main subtypes of the defect are type I with severe mental retardation and succinyladenosine/succinyl-AICAriboside ratios around 1, and type II with slight mental delay and succinyladenosine/succinyl-AICAriboside ratios around 4. We report that in fibroblasts of type I patients, the activity of ASase with both adenylosuccinate and succinyl-AICAR is about 30% of normal. In contrast, in type II fibroblasts, the activity with adenylosuccinate is only 3% of normal, whereas that with succinyl-AICAR is also 30% of normal. If also present in other tissues, this non-parallel deficiency provides an explanation for the higher concentration of succinyladenosine in type II. In type I fibroblasts, ASase is further characterized mainly by a 3-fold to 4-fold increase in Km for succinyl-AICAR, and by retarded elution from an anion exchanger. In type II fibroblasts, ASase is characterized by a similar increase in Km for succinyl-AICAR but by a potent inhibition by KCl and nucleoside triphosphates, and by a normal elution profile. These results suggest a modification of the surface charge of ASase in type I, and the addition of one or more positively charged residues in the active site in type II.
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Affiliation(s)
- F Van den Bergh
- Laboratory of Physiological Chemistry, International Institute of Cellular and Molecular Pathology, Brussels, Belgium
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Laikind PK, Seegmiller JE, Gruber HE. Detection of 5'-phosphoribosyl-4-(N-succinylcarboxamide)-5-aminoimidazole in urine by use of the Bratton-Marshall reaction: identification of patients deficient in adenylosuccinate lyase activity. Anal Biochem 1986; 156:81-90. [PMID: 3740420 DOI: 10.1016/0003-2697(86)90158-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The Bratton-Marshall reaction can be used to identify patients with adenylosuccinate lyase deficiency. These patients excrete in their urine the dephosphorylated derivative of the de novo purine synthesis intermediate 5'-phosphoribosyl-4-(N-succinylcarboxamide)-5-aminoimidazole (SAICAR). The test described here depends on a coupling reaction of N-1-naphthylethylenediamine with diazotized ribosyl-4-(N-succinylcarboxamide)-5-aminoimidazole giving rise to a fast developing purple chromaphore with a maximum absorbance at 555 nm. Using the closely related compound ribosyl-5-amino-4-imidazolecarboxamide (AICA riboside) as a standard, concentrations as low as 1.0 microM produce a visible color change. The absorption at 555 nM of the azo compound increases as a linear function of the concentration of AICA riboside in the reaction. The use of a filter-paper dipstick for urine sampling and storage is also described. The two metabolites which are present in increased concentration in biological fluids of adenylosuccinate lyase deficient patients are stable on the dipstick for at least 60 days when stored at room temperature (25 degrees C).
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Laikind PK, Gruber HE, Jansen I, Miller L, Hoffer M, Seegmiller JE, Willis RC, Jaeken J, Van den Berghe G. Purine biosynthesis in Chinese hamster cell mutants and human fibroblasts partially deficient in adenylosuccinate lyase. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1986; 195 Pt B:363-9. [PMID: 2876593 DOI: 10.1007/978-1-4684-1248-2_57] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Gruber HE, Jansen I, Willis RC, Seegmiller JE. Alterations of inosinate branchpoint enzymes in cultured human lymphoblasts. BIOCHIMICA ET BIOPHYSICA ACTA 1985; 846:135-44. [PMID: 2861860 DOI: 10.1016/0167-4889(85)90119-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
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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Sabina RL, Patterson D, Holmes EW. 5-Amino-4-imidazolecarboxamide riboside (Z-riboside) metabolism in eukaryotic cells. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)88943-8] [Citation(s) in RCA: 106] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Hsie AW, Casciano DA, Couch DB, Krahn DF, O'Neill JP, Whitfield BL. The use of Chinese hamster ovary cells to quantify specific locus mutation and to determine mutagenicity of chemicals. A report of the gene-tox program. Mutat Res 1981; 86:193-214. [PMID: 7022191 DOI: 10.1016/0165-1110(81)90024-5] [Citation(s) in RCA: 115] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Hochstadt J, Ozer HL, Shopsis C. Genetic alteration in animal cells in culture. Curr Top Microbiol Immunol 1981; 94-95:243-308. [PMID: 6171390 DOI: 10.1007/978-3-642-68120-2_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Gupta RS. A novel synergistic effect of alanosine and guanine on adenine nucleotide synthesis in mammalian cells. Alanosine as a useful probe for investigating purine nucleotide metabolism. J Cell Physiol 1980; 104:241-8. [PMID: 7410492 DOI: 10.1002/jcp.1041040214] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A novel synergistic effect of the antitumor agent alanosine (2-amino-3-(hydroxynitrosoamino) propionic acid), which specifically inhibits the enzyme adenylosuccinate synthetase (ASS) and guanine on the growth of Chinese hamster ovary (CHO) cells and human diploid fibroblasts (HDF) has been observed. In the presence of subinhibitory concentrations of alanosine, both CHO cells and the HDF show excessive sensitivity to exogenous guanine--a phenotype which closely resembles that seen with some of the mutants containing reduced enzymatic activity of ASS. The growth inhibitory effects of alanosine, or alanosine and guanine, on CHO cells are completely reverted by the addition of adenine to the culture medium, and the synergistic effect of guanine is not observed in mutants which lack the enzyme hypoxanthine-guanine phosphoribosyl transferase. These resuls suggest that guanine nucleotides exert a regulatory effect on the activity of the enzyme adenylosuccinate synthetase. The ability to confer the guanine-sensitive phenotype and its modulation by subinhibitory concentrations of alanosine in different cell types indicates that alanosine provides a useful probe for investigating the regulation of purine nucleotide metabolism in mammalian cells.
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Oates DC, Vannais D, Patterson D. A mutant of CHO-K1 cells deficient in two nonsequential steps of de novo purine biosynthesis. Cell 1980; 20:797-805. [PMID: 7418008 DOI: 10.1016/0092-8674(80)90326-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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12
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[3H]Amino acid selection of aminoacyl-tRNA synthetase mutants of CHO cells: Evidence of homo- vs. hemizygosity at specific loci. ACTA ACUST UNITED AC 1979. [DOI: 10.1007/bf01538846] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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13
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Ullman B, Clift SM, Cohen A, Gudas LJ, Levinson BB, Wormsted MA, Martin DW. Abnormal regulation of de novo purine synthesis and purine salvage in a cultured mouse T-cell lymphoma mutant partially deficient in adenylosuccinate synthetase. J Cell Physiol 1979; 99:139-51. [PMID: 222775 DOI: 10.1002/jcp.1040990115] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The isolation and characterization of a mutant murine T-cell lymphoma (S49) with altered purine metabolism is described. This mutant, AU-100, was isolated from a mutagenized population of S49 cells by virtue of its resistance to 0.1 mM 6-azauridine in semisolid agarose. The AU-100 cells are resistant to adenosine mediated cytotoxicity but are extraordinarily sensitive to killing by guanosine. High performance liquid chromatography of AU-100 cell extracts has demonstrated that intracellular levels of GTP, IMP, and GMP are all elevated about 3-fold over those levels found in wild type cells. The AU-100 cells also contain an elevated intracellular level of pyrophosphoribosylphosphate (PPriboseP), which as in wild type cells is diminished by incubation of AU-100 cells with adenosine. However AU-100 cells synthesize purines de novo at a rate less than 35% of that found in wild type cells. In other growth rate experiments, the AU-100 cell line was shown to be resistant to 6-thioguanine and 6-mercaptopurine. Levels of hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) measured in AU-100 cell extracts, however, are 50-66% greater than those levels of HGPRTase found in wild type cell extracts. Nevertheless this mutant S49 cell line cannot efficiently incorporate labeled hypoxanthine into nucleotides since the salvage enzyme HGPRTase is inhibited in vivo. The AU-100 cell line was found to be 80% deficient in adenylosuccinate synthetase, but these cells are not auxotrophic for adenosine or other purines. The significant alterations in the control of purine de novo and salvage metabolism caused by the defect in adenylosuccinate synthetase are mediated by the resulting increased levels of guanosine nucleotides.
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Irwin M, Oates DC, Patterson D. Biochemical genetics of Chinese hamster cell mutants with deviant purine metabolism: isolation and characterization of a mutant deficient in the activity of phosphoribosylaminoimidazole synthetase. SOMATIC CELL GENETICS 1979; 5:203-16. [PMID: 483121 DOI: 10.1007/bf01539161] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A new purine-requiring mutant of Chinese hamster ovary cells (CHO-Kl) is described. This mutant, Ade-G, grows on aminoimidazole carboxamide, hypoxanthine, or adenine. It complements all eight of our other previously described Ade- mutants. Biochemical analysis of de novo purine synthesis in whole cells suggests that Ade-G is capable of the first four reactions of de novo purine biosynthesis and that it synthesizes and accumulates phosphoribosylformylglycinamidine (FGAM). Direct enzyme assay in cell-free extracts confirms that Ade-G is defective in phosphoribosylaminoimidazole synthetase activity and does not convert FGAM to phosphoribosylaminoimidazole (AIR), the next intermediate in the de novo biosynthetic pathway.
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Tu AS, Patterson D. Characterization of a guanine-sensitive mutant defective in adenylo-succinate synthetase activity. J Cell Physiol 1978; 96:123-32. [PMID: 659517 DOI: 10.1002/jcp.1040960115] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
A contingent auxotrophic mutant of CHO-Kl cell is described. This mutant grows in minimal medium. Its growth is inhibited by the exogenous addition of guanine at levels which do not affect the wild type parent. Adenine reverses the guanine effect. This mutant does not complement ade-H (defective in adenylosuccinate synthetase) and has been denoted as ade-HG because of its guanine sensitivity. Some partial revertants of ade-H are found to be also sensitive to guanine, suggesting a close relationship between the ade-H locus and the guanine sensitivity. Studies of 14C-hypoxanthine incorporation into nucleotides indicated that ade-HG has some adenylosuccinate synthetase activity whether it is pre-exposed to guanine or not. Early de novo purine synthesis in ade-HG, however, is greatly inhibited when pre-exposed to guanine. This inhibition of purine synthesis by guanine is reversible and its recovery is facilitated by adenine.
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Adair GM, Thompson LH, Lindl PA. Six complementation classes of conditionally lethal protein synthesis mutants of CHO cells selected by 3H-amino acid. SOMATIC CELL GENETICS 1978; 4:27-44. [PMID: 628883 DOI: 10.1007/bf01546491] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Using a tritiated amino acid suicide procedure designed specifically to select conditional protein synthesis mutants, we have isolated and characterized a large number of such mutants of Chinese hamster ovary cells. All of the mutants are genetically stable and behave as recessives in somatic cell hybrids. Most of the new mutants are phenotypically dependent on the concentration of a specific amino acid as well as on temperature. In addition to identifying many additional leucyl- and asparagyl-tRNA synthetase mutants, complementation analysis has distinguished four new genetic classes representing methionine-, glutamine-, histidine-, and arginine-dependent mutants. Biochemical characterization of representative mutants from each of these six classes has identified the primary lesions as being defective aminoacyl-tRNA synthetases. Our selection results further demonstrate the high specificity of the 3H-amino acid procedure for isolating protein synthesis mutants. Reconstruction experiments performed with two representative mutants indicated a selection efficiency of approximately 10% under standard conditions.
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Thompson LH, Lofgren DJ, Adair GM. CHO cell mutants for arginyl-, asparagyl-, glutaminyl-, histidyl- and methionyl-transfer RNA synthetases: identification and initial characterization. Cell 1977; 11:157-68. [PMID: 559545 DOI: 10.1016/0092-8674(77)90326-9] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Tu AS, Patterson D. Biochemical genetics of Chinese hamster cell mutants with deviant purine metabolism. VI. Enzymatic studies of two mutants unable to convert inosinic acid to adenylic acid. Biochem Genet 1977; 15:195-210. [PMID: 849250 DOI: 10.1007/bf00484561] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Ade-H and ade-I are two auxotrophic mutants of Chinese hamster ovary (CHO-K1) cells which specifically require adenine as the purine source to grow. The enzymatic defects of these mutants were examined in cell-free extracts. It was found that ade-H did not have any detectable adenylosuccinate synthetase activity and ade-I was defective in the adenylosuccinate lyase enzyme. The relevance of adenine-requiring mutants to the study of the regulation of purine metabolism in mammalian cells is discussed.
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Patterson D, Jones C. Biochemical genetics of Chinese hamster cell mutants with deviant purine metabolism: isolation, selection, and characterization of a mutant lacking hypoxanthine-guanine phosphoribosyltransferase activity by nutritional means. SOMATIC CELL GENETICS 1976; 2:429-39. [PMID: 800293 DOI: 10.1007/bf01542723] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Mutants of the Chinese hamster ovary cell derived from CHO-K1 have been selected for lack of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) (HGPRT) without the use of a drug-resistance protocol. The procedure depends on the use of a parental strain carrying a mutation making it unable to synthetize purines and thus dependent upon exogenously added purines for growth. The standard "BUdR-visible-light" procedure is then used to select those cells which can use adenine but cannot use hypoxanthine as a purine source. These cells are shown to be thioguanine resistant, to be unable to incorporate exogenously added hypoxanthine into purine nucleotides, to complement our other adenine-specific purine auxotrophs, Ade-H and Ade-I but not to complement a cell isolated by virtue of thioguanine resistance, and to lack the activity of HGPRT. The use of such multiply marked mutants and cells related to them for further analysis of purine nucleotide biosynthesis and interconversion is discussed.
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