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

---

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

In the present study, hypoxanthine phosphoribosyltransferase (HPRT) has been investigated in fibroblasts of 19 patients from 16 different families with HPRT deficiency, concerning activity, incorporation of 14C-hypoxanthine, and growth in 8-azaguanine and HAT (hypoxanthine, azaserine, thymidine containing) selection media. According to these data we could classify the patients into 5 groups (patients with classical Lesch-Nyhan syndrome and patients with HPRT variants of types A, B, C, D). In 3 groups (patients with classical Lesch-Nyhan syndrome, HPRT variants C and D), a correlation of residual HPRT activity with the incorporation of 14C-hypoxanthine as well as growth in 8-azaguanine and HAT selection was observed. The variant A, from a patient with the classical Lesch-Nyhan syndrome, exhibited higher HPRT activity than that from all the other patients with the Lesch-Nyhan syndrome. However, the values of hypoxanthine incorporation and growth in selection media were as in the classical syndrome. The cells of variant B were resistant to azaguanine and grew in HAT selection media in the range of control cells, but had HPRT residual activities similar to those of variants A and C. For the characterization of the genetic heterogeneity of HPRT, it seems necessary to study the enzymatic properties in cell extracts as well as the purine uptake and proliferation of cells in different selection media.
...
PMID:Studies in fibroblasts of patients with the Lesch-Nyhan syndrome and HPRT variants. Correlation of HPRT activity with hypoxanthine utilization and growth in selection media. 652 1

Chloramphenicol-resistant (CAPr) reconstituted cells and cybrids were isolated by fusion of karyoplasts (or intact cells) of mouse amelanotic melanoma B16 cells with cytoplasts of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) -deficient, CAPr rat myoblastic cells, L6TG.CAPr, and double selection in HAT medium containing CAP. Reconstituted cells or cybrids exhibited unique cellular arrangement, and about one third of the isolated clones expressed high tyrosinase activity and marked melanin synthesis, although the parental mouse cells expressed low tyrosinase activity and the parental rat cells did not express tyrosinase activity. These phenotypic changes have been stable for more than a year. The phenotypic reversions of these clonal cells were induced by treatment with a tumor promoter. There were changes in the morphology of the treated cells to that of the mouse B16 cells and extinction of tyrosinase activity and melanin synthesis in pigmented clonal cells. These phenotypic changes and reversions induced by a promoter were repeatedly reversible.
...
PMID:Induction of supermelanin synthesis and morphological changes in interspecific reconstituted cells and its reversal by tumor promoter. 681 81

A significant and reproducible enhancement of purine nucleotide synthesis from hypoxanthine occurs in HAT medium, when communication-competent hypoxanthine-guanine phosphoribosyltransferase (HGPRT+) cells are co-cultured with communication-competent (HGPRT-) LN cells. This enhancement of purine nucleotide synthesis is dependent upon the hypoxanthine concentration and upon the ratio of (HGPRT-): (HGPRT+) cells. Based upon these results a simple biochemical method for the detection of inhibitors of metabolic cooperation between (HGPRT+) cells and (HGPRT-) LN cells is presented. The biochemical method distinguishes inhibitors of metabolic cooperation from inhibitors of hypoxanthine uptake, of hypoxanthine phosphorylation and of nucleic acid synthesis, as well as from general metabolic inhibitors. This method has the advantage that it can be used on a relatively large number of cells, it is simple and not time-consuming, and distinguishes the inhibition of metabolic cooperation by compounds that have a variety of sites of inhibition.
...
PMID:Biochemical assay of inhibitors of metabolic cooperation. 685 23

Branched-chain aminotransferase (BCT) catalyzes the reversible transamination of the branched-chain alpha-keto acids to the branched-chain L-amino acids. Since branched-chain L-amino acids (L-isoleucine, L-leucine, and L-valine) are essential for cell growth, cells which lack BCT were unable to proliferate in media containing alpha-keto acids in place of the corresponding L-amino acids. CHW-1102, a Chinese hamster cell line, lacks BCT and does not grow in alpha-keto acid media. Somatic cell hybrids were made by the fusion of CHW-1102 (HPRT-) with several human cell lines and isolated on HAT medium. Growth assays of hybrid clones on alpha-keto acid selection media independent of the HAT selection medium indicated two cell hybrid phenotypes: either (1) the hybrid clone, like the parental CHW-1102, could not utilize alpha-keto acid media, or (2) the hybrid could proliferate on all three alpha-keto acid media. The ability of hybrid cells to proliferate on alpha-keto acid media correlated with the presence of either of two human genes which independently complemented the Chinese hamster deficiency. Two human genes. BCT1 assigned to chromosome 12 and BCT2 assigned to chromosome 19, were demonstrated to code for the expression of two molecular forms of BCT.
...
PMID:Branched-chain aminotransferase deficiency in Chinese hamster cells complemented by two independent genes on human chromosomes 12 and 19. 693 2

Fusion of 6-thioguanine-resistant mouse neuroblastoma to HeLa whole and minicells generated neuroblastoma HPRT revertants in addition to true cell hybrids. All revertants contained HPRT with decreased electrophoretic mobility and heat stability relative to wild-type mouse enzyme. Revertant HPRT expression was dependent on continuous HAT selection. Quantitative immunoadsorption experiments showed that revertants with low HPRT specific activity had wild-type levels of HPRT protein while a revertant with high apparent activity (NBR4) contained elevated levels of variant protein. HPRT extracted from NBR4 had decreased affinity of both hypoxanthine and PRPP relative to wild type. Evidence is presented that HPRT elevation is dependent on the reversion process itself.
...
PMID:Cell fusion-induced mouse neuroblastomas HPRT revertants with variant enzyme and elevated HPRT protein levels. 702 97

Because clothing enhances the gonadal temperature in the human male and because as a consequence of that the spontaneous mutation rate might be increased, a study was undertaken to determine the effect of temperature on mutation towards HPRT deficiency in human diploid skin fibroblasts. Culturing of the cells in HAT medium containing azaserine, to remove pre-existing mutants, was highly mutagenic. Some results suggested that azaserine acts as an indirect mutagen. The mutational process in the presence of azaserine was influenced by temperature, a rise in temperature from 33 to 37 degrees C leading to a more than 10-fold increase in mutation rate per cell generation. This temperature dependence, taken as a starting point for the estimation of the consequences of the rise in gonadal temperature, could be responsible for an increase of 135% in the incidence of a sex-linked lethal (Lesch-Nyhan) in the human population. Epidemiological data on the frequency of Lesch-Nyhan disease and on the ratio of paternal and maternal mutations leading to Lesch-Nyhan disease do not contradict the findings in the cultured cells.
...
PMID:Effect of temperature on mutation in cultured human skin fibroblasts. 708 11

A rapidly-growing, HAT-sensitive cell line LICR-LON-HMy2 has been derived from the ARH-77 human plasma cell leukemia-derived line. It lacks the enzyme hypoxanthine phosphoribosyltransferase (EC 2.4.2.8). Hybrids have been reproducibly made for more than a year and in independent laboratories with lymphocytes from tonsils, lymph nodes and peripheral blood and tonsil lymphocytes cultured with antigens. The parent line and hybrids are very robust in culture and double in 20-30 h. Hybrids clone easily and have stable karyotypes, most with modal numbers in the sixties. Stable Ig secretion patterns have been observed over 20-30 passages, and after cloning. It was estimated that about half the hybrids produce new immunoglobulin chains in addition to the parent cell line's IgG1 (kappa light chain). High, but not limiting, density hybridoma cultures (approximately 5 x 10(5) cells/ml) typically produce 0.25-2 micrograms/ml immunoglobulin per day, but some hybrids produce more. A high-secreting variant of LICR-LON-HMy2 has been derived. The LICR-LON-HMy2 line is human and is distinct from the HAT-sensitive human B cell-lines SKO-007 and GM 1500-6TG Al 2. It is available for distribution.
...
PMID:A human-hybridoma system based on a fast-growing mutant of the ARH-77 plasma cell leukemia-derived line. 714 Aug 10

Mouse teratocarcinoma cells (OTT6050) deficient for thymidine kinase were fused with rat hepatoma cells ( Fu5AH ) deficient for hypoxanthine phosphoribosyltransferase using inactivated Sendai virus. The hybrid cells were selected and cultured in the presence of HAT medium. A clonally established hybrid cell line ( As3 ), which in addition to its mouse genome contains several rat chromosomes, expresses rat specific enzyme variants and produces large primarily undifferentiated tumors, with some hepatoma characteristics in athymic nude mice. To reveal the in vivo developmental potential of these cells and to determine whether, under different experimental conditions, they are capable of participating in tissue differentiation, the As3 cells were injected into mouse blastocysts from the C57BL/6 strain. The experimental blastocysts were then transferred into the uteri of pseudopregnant foster mothers to allow further development. From a total of 212 blastocysts transplanted, 61 fetuses developed and were analysed for As3 contributions between the 10th and 18th day of gestation. Four fetuses at day 18 showed hybrid cell participation in their livers and a few organs of only endo-mesodermal origin, as judged from the presence of rat-specific enzyme variants. The enzymes were organ-specifically expressed (e.g., lactate dehydrogenase) or appeared newly during in situ differentiation while being absent in the original hybrid cells (e.g., glycerol-3-phosphate dehydrogenase). During short in vitro culture of the chimaeric organs, it was possible to select for the hybrid cells which reverted to an enzyme pattern simiar to but not identical with the As3 cell line and different to that observed in situ.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Tissue preference and differentiation of malignant rat x mouse hybrid cells in chimaeric mouse fetuses. 718 53

RJK39 is a clone of Chinese hamster cells carrying a mutation which inactivates hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and reduces the apparent molecular weight of the enzyme. Using mutagens, we have isolated subclones of RJK39 which will grow in the counterselective HAT medium. Some continue to be HGPRT-deficient and survived the selection because they are resistant to aminopterin. In all but one of the HGPRT-positive revertants, the molecular weight of the enzyme returned to the wild-type value. However, the phenotypes of several of those strains indicate they produce altered forms of HGPRT, and one can conclude that second-site mutations must be able to cause intragenic suppression of the original mutation in RJK39. One of the revertants is pseudotetraploid and functionally heterozygous at the HGPRT locus. Segregation studies with that clone localized the genes for HGPRT, glucose-6-phosphate dehydrogenase, and phosphoglycerate kinase to the short arm of the Chinese hamster X chromosome.
...
PMID:Reversion of a mutation affecting the molecular weight of HGPRT: intragenic suppression and localization of X-linked genes. 719 35

Eight Chinese hamster clones (CHO-K1) growing at the 30 mg/ml concentration of 8-azaguanine (AG) were studied. Clones were differentiated by their resistance to AG and to 6-thioguanine, by their plating efficiency on HAT medium, and by the level of hypoxantine incorporation in cells. The differences in phenotypic properties were shown to be associated with variability in hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity. HPRT Michaelis constant (KM) for hypoxanthine and phosphoribosylpyrophosphate, and maximal reaction rate (Vm) offered considerable differences between all the resistant clones and sensitive cells. The only possible reason of these differences is a change in the HPRT coding locus. According to the results of the analysis of B15-4b-4 subclones, phenotypic and HPRT activity differences are also connected with each other; however, all subclones have the same KM of HPRT as that of the parental clone. So, differences in HPRT activity (and in Vm) may reflect changes in the HPRT content in cells of subclones. Hence, phenotypic heterogeneity of AG-resistant clones is determined by the interaction of mutational changes in the HPRT locus, and hereditable changes of genetic activity, responsible for variation of HPRT quantity in cells.
...
PMID:[Hereditary changes in gene activity as 1 of the causes of phenotypic heterogeneity in 8-azaguanine-resistant Chinese hamster cells (CHO-K1)]. 731 48


<< Previous 1 2 3 4 5 6 7 Next >>

---