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:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of 5-fluorouracil (FUra) treatment on thymidine kinase (TKase) activity were examined in vivo in CD8F1 mice bearing first generation CD8F1 mouse mammary tumors. TKase activity was not affected by low dose FUra25 (25 mg/kg), a dose which substantially inhibited thymidylate synthase (TSase), but was severely inhibited 24 hr following treatment with FUra100, a weekly maximally tolerated dose, as judged by activity measurements and labeling of DNA with [3H]thymidine. The amount of (FU)RNA was increased markedly with increasing FUra dose from 0.4 nmol/mg DNA at FUra25 to 2.2 nmol/mg DNA at FUra100. At FUra100, TKase activity gradually declined over 24 hr to less than 10% of the control value, remained low for a further 48 hr, and then was gradually restored to control levels by 168 hr. The loss of TKase activity followed the incorporation of FUra into RNA which peaked at 4-5 hr. TKase activity was not restored by removal of endogenous inhibitors but was restored by treatment with uridine. TKase activity was not inhibited by therapeutic levels of methotrexate (300 mg/kg). TKase from murine colon 38 carcinoma was also severely inhibited, but the activity from colon 26 was only partially (50%) inhibited. Ornithine decarboxylase was also inhibited by FUra100 treatment in the CD8F1 tumor. These results demonstrate that certain short-lived, proliferation-related enzymes are affected by FUra doses higher than those required for TSase inhibition, and this effect appears to correlate with incorporation of FUra into RNA. Thus, in some tumors high doses of FUra can inhibit salvage as well as de novo synthesis of thymidylate providing an increased block of DNA synthesis and increased therapeutic advantage.
...
PMID:Loss of murine tumor thymidine kinase activity in vivo following 5-fluorouracil (FUra) treatment by incorporation of FUra into RNA. 172 9

The pathway for the acquisition of thymidylate in the obligate bacterial parasite Rickettsia prowazekii was determined. R. prowazekii growing in host cells with or without thymidine kinase failed to incorporate into its DNA the [3H]thymidine added to the culture. In the thymidine kinase-negative host cells, the label available to the rickettsiae in the host cell cytoplasm would have been thymidine, and in the thymidine kinase-positive host cells, it would have been both thymidine and TMP. Further support for the inability to utilize thymidine was the lack of thymidine kinase activity in extracts of R. prowazekii. However, [3H]uridine incorporation into the DNA of R. prowazekii was demonstrable (973 +/- 57 dpm/3 x 10(8) rickettsiae). This labeling of rickettsial DNA suggests the transport of uracil, uridine, uridine phosphates (UXP), or 2'-deoxyuridine phosphates, the conversion of the labeled precursor to thymidylate, and subsequent incorporation into DNA. This is supported by the demonstration of thymidylate synthase activity in extracts of R. prowazekii. The enzyme was determined to have a specific activity of 310 +/- 40 pmol/min/mg of protein and was inhibited greater than or equal to 70% by 5-fluoro-dUMP. The inability of R. prowazekii to utilize uracil was suggested by undetectable uracil phosphoribosyltransferase activity and by its inability to grow (less than 10% of control) in a uridine-starved mutant cell line (Urd-A) supplemented with 50 microM to 1 mM uracil. In contrast, the rickettsiae were able to grow in Urd-A cells that were uridine starved and supplemented with 20 microM uridine (117% of control). However, no measurable uridine kinase activity could be measured in extracts of R. prowazekii. Normal rickettsial growth (92% of control) was observed when the host cell was blocked with thymidine so that the host cell's dUXP pool was depressed to a level inadequate for growth and DNA synthesis in the host cell. Taken together, these data strongly suggest that rickettsiae transport UXP from the host cell's cytoplasm and that they synthesize TTP from UXP.
...
PMID:Acquisition of thymidylate by the obligate intracytoplasmic bacterium Rickettsia prowazekii. 190 Feb 79

The effect of 3'-deoxythymidin-2'-ene (d4T) on the metabolism of exogenously supplied radiolabeled nucleosides was investigated. Following a 24-hr exposure to 250 microM d4T, we observed no significant effect on the incorporation of [3H]thymidine or [3H]deoxycytidine into DNA. In contrast, the amounts of [3H]uridine, [3H]deoxyuridine, and [3H]cytidine were significantly lower than those incorporated by control cultures. d4T had no significant effect on the incorporation of [3H]uridine or [3H]cytidine into RNA, or the incorporation of 3H-labeled amino acids into protein. In d4T-treated cells the relative proportions of [3H]dTMP, [3H]dTDP, and [3H]dTTP formed did not change but their absolute concentrations were increased. d4T significantly reduced the level of [3H]dUMP, and a parallel decrease in [3H]dTMP derived from [3H]dUMP was also evident. d4T increased the amounts of labeled deoxycytidine metabolites formed, with increased dCMP levels the most prominent. In a cell-free extract, [3H]d4T was phosphorylated at a rate of 1.6 pmol/30 min. Increasing concentrations of both thymidine and deoxyuridine inhibited the phosphorylation of [3H]d4T with IC50 values of 5.7 and 35 microM respectively. d4T was found to be a weak substrate for purified H9 cytosolic thymidine kinase (Km = 138 microM) and a weak competitive inhibitor of thymidine and deoxyuridine phosphorylation by this enzyme (Ki = 1.37 and 0.33 mM respectively).
...
PMID:Effect of 3'-deoxythymidin-2'-ene (d4T) on nucleoside metabolism in H9 cells. 215 60

Thymidine auxotrophs (B3T) of rat nerve-like cells (B103) were isolated. B103 cells were preincubated in a thymidine medium and mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Afterward, cells were incubated in a medium supplemented with dialyzed fetal calf serum and then treated with 5-fluorodeoxyuridine for 24 h. Next, cells were grown in a thymidine medium for twenty days. Thymidine auxothrophs were thus obtained and one clone of them was designated B3T cells. The modal number of chromosomes in B3T cells was 85. Growth tests revealed the following interesting facts: (1) The medium containing pyrazofurin and uridine could not support the growth of B3T cells, but the addition of thymidine to such a medium enabled cells to grow. (2) Even deoxyuridine supported the growth of B3T cells when added to the medium of pyrazofurin and uridine. These findings suggest that the catalytic ability of thymidylate synthetase in B3T cells may have decreased, probably due to the decreased affinity of the enzyme molecules to the substrate (dUMP), and that thymidine kinase activity was high enough to support the growth of B3T cells. B3T cells have maintained the ability to differentiate and extend neurites in response to dibutyryl-cyclic AMP as also demonstrated in wild cells (B103). B3T cells will be available for genetical and molecular biological studies of neuronal cells.
...
PMID:Isolation of thymidine-requiring variants from rat nerve-like cells. 216 41

Mycobacterium microti incorporated a wide range of exogenously supplied pyrimidines into its nucleic acids. M. avium incorporated a relatively narrow range of pyrimidines but both M. avium and M. microti when recovered after growth in vivo incorporated a slightly wider range of pyrimidines than the same strains grown in vitro. M. microti and M. leprae could not take up uridine nucleotides directly but could utilize the pyrimidines by hydrolysing them to uridine and then taking up the uridine. Pyrimidine biosynthesis, judged by the ability to incorporate carbon from CO2 or aspartate into pyrimidines was readily detected in non-growing suspensions of M. microti and M. avium harvested from Dubos medium, which does not contain pyrimidines. The biosynthetic activity was diminished in mycobacteria grown in vivo when there is likely to be a source of pyrimidines which they might use. Relative activities for pyrimidine biosynthesis de novo in M. microti were 100 for cells isolated from Dubos medium, 6 for cells isolated from Dubos medium containing the pyrimidine cytidine and 11 from cells recovered after growth in mice. In contrast, relative activities for a scavenging reaction, uracil incorporation, were 100, 71 and 59, respectively. Three key enzymes in the pathway of pyrimidine biosynthesis de novo were detected in M. microti and M. avium. Two, dihydroorotate synthase and orotate phosphoribosyltransferase appeared to be constitutive in M. microti and M. avium. Aspartate transcarbamoylase activity was higher in these mycobacteria grown in vivo than in Dubos medium but it was repressed in M. microti or M. avium grown in Dubos medium in the presence of 50 microM-pyrimidine. Aspartate transcarbamoylase was strongly inhibited by the feedback inhibitors ATP, CTP and UTP. Enzymes for scavenging pyrimidines were detected at low specific activities in all mycobacteria studied. Activities of phosphoribosyltransferases, enzymes that convert bases directly to nucleotides, were not related to the ability of intact mycobacteria to take up pyrimidine bases while activities of pyrimidine nucleoside kinases were generally related to the ability of intact mycobacteria to take up nucleosides. Phosphoribosyltransferase activity for uracil, cytosine, orotic acid and--in organisms grown in Dubos medium with 50 microM-uridine-thymine, as well as kinases for uridine, deoxyuridine, cytidine and thymidine were detected in M. microti. However, M. avium only contained uracil and orotate phosphoribosyltransferase, uridine, cytidine and thymidine kinase, and additionally deoxyuridine kinase when grown axenically with 50 microM-uracil, reflecting its more limited abilities in pyrimidine scavenging.
...
PMID:Biosynthesis and scavenging of pyrimidines by pathogenic mycobacteria. 219 Oct 77

The levels of serum deoxythymidine kinase (s-dTK) were investigated for 127 patients suffering hematological malignancy by a sensitive method using [125I]-iododeoxy-uridine as substrate. It was found that the deoxythymidine kinase activity in the sera of these patients was higher than the normal levels in adults. It was also found that the levels of s-dTK in the progressive stage were much higher than those in the indolent stage. These results suggest that high levels of s-dTK in hematological malignancy may reflect the extent of disease and that this activity may be derived from proliferating leukemic cells. The deoxythymidine kinase activity in the extracts derived from cultured cell lines and clinical specimens indicated that leukemic cells contained much higher activity than normal cells.
...
PMID:Serum deoxythymidine kinase as a progressive marker of hematological malignancy. 238 58

A study was made of the in vivo effects of equitoxic doses of AT-125 and 5-FU combination, being administered either simultaneously (% ILS 152) or with a 6-h pretreatment with AT-125 (% ILS 184). To examine the biochemical basis for the scheduled synergism, measurements were made of the concentration of PRPP, the specific activities of CPS II, cytidine, thymidine, uridine, deoxyuridine kinases, and fluorinated nucleotide formation in P388 tumors and the small intestine. Two hours after in vivo simultaneous treatment of mice bearing tumors the concentration of PRPP increased 9- and 6-fold above baseline in the tumor and the small intestine, respectively. In the AT-125 pretreatment arm the concentration of PRPP increased 18- and 7-fold above baseline in the tumor and the small intestine, respectively. CPS II activity was reduced to 28%-18% of control in the tumors in the simultaneous and pretreatment groups, respectively, whereas it remained unchanged in the small intestine. Specific activities of cytidine kinase (5.5 +/- 1), thymidine kinase (4.0 +/- 1.6), uridine kinase (35.6 +/- 6.5), and deoxyuridine kinase (2.4 +/- 1.1) nmol/mg protein/h remained unchanged with treatment. In concert with the increased intratumor concentration of PRPP, fluorinated nucleotide formation was proportionally increased in the treatment arms. These results indicate the importance of drug scheduling of the above two agents in treating P388 leukemia.
...
PMID:Biochemical mechanisms for the scheduled synergism of (alpha S, 5S)-2 amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid and 5-fluorouracil in P388 leukemia. 240 73

A study was made of the effect of an DNA methylation inhibitor 5-azacytidine (azaC) on the frequency of reversion to a thymidine kinase-positive (TK+) phenotype in 5-bromodeoxy-uridine (BrdU)-resistant subclones obtained from clones of Chinese hamster cells transformed by thymidine kinase gene (tk-gene) of Herpes simplex virus type 1 (HSV1). It is shown that in 8 of 15 BrdU-resistant subclones azaC increases 2-1000-fold the frequency of reversion to TK+ phenotype. Variations in the inducibility of reversions to TK+ phenotype indicate that the DNA methylation associated with TK- phenotype affects but differently tk gene of HSV1. Cultivation of TK+ cells of transformant clones in the presence of azaC may lead to stabilization (or decrease in the rate of the loss) of TK+ phenotype, or may not influence the stability of transformant phenotype. The reaction of TK+ cells of transformant clones depends both on genetically determined rate of the loss of TK+ phenotype, and on the structure of transforming DNA introduced to cells. A conclusion is drawn that the TK- phenotype of transformant clone cells arises due to processes which are not associated with methylation of tk gene of HSV1 in spite of the fact that such a methylation may later stabilize significantly the TK- phenotype.
...
PMID:[Genetic transformation of somatic cells. VIII. The effect of the DNA methylation inhibitor 5-azacytidine on the stability of thymidine kinase-negative and -positive phenotypes of transformant clone cells]. 241 97

The cytogenetic study of colorectal carcinomas is consistent with the following sequence in the tumor evolution: rearrangement of chromosome 17 with loss of 17p and often gain of 17q, loss of chromosome 18, frequent del(5q), frequent del(1p) correlated with the gain of an early replicating X. At least one gene directly involved in nucleotide synthesis, especially in the de novo pathways for thymidine is located on each of these chromosomes or chromosomes segments. A model established on the gene dosage effect, which likely results of these chromosome imbalances, may be proposed: (1) increase of thymidine kinase activity (chromosome 17q) and thus of the salvage pathway of thymidine synthesis (2) decrease of thymidine de novo pathways by decreased of thymidylate synthase (chromosome 18) and of dihydrofolate reductase (chromosome 5q) and thus accumulation of 2'-deoxyuridine-5'-P, which saves 2'-deoxycytidine 5'-P (3) decrease of cytidylate (or uridylate) kinase (chromosome 1p) and thus accumulation of 2-deoxycytidine-5-PP and of uridine-5-P (UMP) decreasing the metabolisation of orotidine-5'-P, precursor of 2-deoxycytidine-5-PP, which (4) saves -D-5-ribosyl-PP (PRPP) or even conversion of orotidine-5'-P in PRPP. The later is the immediate precursor of nucleotides in their major salvage pathways synthesis: PRPP + base----nucleotide + PPi. This reaction which would be much activated needs hypoxanthine phosphorybosyl transferase (HPRT). Its gene is carried by chromosome X which is here duplicated in its active early replicating form.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Induction of increased salvage pathways of nucleotide synthesis by dosage effect due to chromosome imbalances may be fundamental in carcinogenesis: the example of colorectal carcinoma. 242 58

The molecular mechanism of interferon action on vaccinia virus-specific immediate early protein synthesis was studied in interferon-treated chick cells. In line with previous observations, the synthesis of total vaccinia WR virus-specific mRNA, thymidine kinase (TK) mRNA, and several other early mRNAs was detectable by short [3H]uridine pulses. Under conditions of over 90% inhibition of poxvirus-specific TK induction, accumulation of TK mRNA was strongly inhibited. Northern blot analysis revealed strong degradation of residual TK mRNA prepared from interferon-treated chick embryo fibroblasts (CEF). Blot hybridization analysis using total vaccinia DNA and restriction fragment N as probes demonstrated a generally reduced steady-state amount of vaccinia virus-specific early mRNAs in interferon-treated CEF. When CEF were infected with a recombinant vaccinia virus strain into the TK gene of which the chloramphenicol acetyltransferase gene had been inserted, CAT activity was far lower in interferon-treated than in untreated CEF. We conclude that signals that specify rapid breakdown of viral TK mRNA in interferon-treated CEF are located in the regions flanking the coding sequences of the viral TK gene.
...
PMID:Reduced steady-state levels of vaccinia virus-specific early mRNAs in interferon-treated chick embryo fibroblasts. 243 97


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---