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

Two forms (Peak A and Peak B) of thymidine kinase [EC 2.7.1.75] from regenerating rat liver cytosol were resolved and partially purified by Deae-cellulose chromatography. Both fractions were identical with respect to their substrate requirement, pH optima, metal requirements, and molecular weight, as judged by their sedimentation in sucrose density gradient centrifugation. Peak B differed from Peak A in heat sensitivity, inhibition by dCTP and Km for thymidine and ATP. Peak B enzyme was the only enzyme found in normal adult liver and Peak A enzyme was the form increasing predominantly in regenerating liver.
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PMID:Two molecular forms of thymidine kinase in the cytosol of regenerating rat liver. 0 19

Using gel filtration chromatography, we find a single peak of deoxythymidine phosphorylating activity in Chlamydomonas reinhardti. This activity has characteristics of a thymidine kinase, in that (1) it will utilize ATP (or dATP) or CTP (or dCTP) as phosphoryl donor, but not AMP or phenyl phosphate, and (2) it is inhibited by dTTP (and less so by dTDP, dUTP, and dUDP) but is unaffected by 3'-5' cyclic AMP. Partially purified chlamydomonas thymidine kinase has a pH optimum near 8.5, and a molecular weight of 80,000 to 85,000 daltons. Kinetic studies indicate a ping-pong mechanism with a Km for thymidine of 1.5 x 10(-7) moles per liter. 5-Bromo- and 5-fluorodeoxyuridine, and to a lesser degree deoxyuridine, are competitive inhibitors, but significant phosphorylation of these nucleotides could not be demonstrated in vitro by thymidine kinase. While thymidine is phosphorylated to dTMP by crude Chlamydomonas extracts, greater than 80% of the product formed by the partially purified enzyme is dTTP. Further, the gel filtration elution position of the single deoxythymidylate kinase activity present in cell extracts coincides with that of thymidine kinase. These results suggest that a multifunctional enzyme, rather than three separate phosphorylating activities, may be responsible for dTTP formation.
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PMID:Characterization of thymidine kinase and phosphorylation of deoxyribonucleosides in Chlamydomonas reinhardti. 4 38

Poly(ADP-ribose) polymerase activity in nuclei isolated from differentiating cardiac muscle of the rat has been characterized and its activity measured during development. Optimum enzyme activity is observed at pH 8.5. Poly(ADP-ribose) polymerase is inhibited by ATP, thymidine, nicotinamide, theophylline, 3-isobutyl-1-methylxanthine and caffeine and stimulated by actinomycin D. The activity measured under optimal assay conditions increases during differentiation of cardiac muscle and is inversely related to the rate of DNA synthesis and to the activities of DNA polymerase alpha and thymidine kinase. When DNA synthesis and the activity of DNA polymerase alpha are inhibited in cardiac muscle of the 1-day-old neonatal rat by dibutyryl cyclic AMP or isoproterenol, the specific activity of poly(ADP-ribose) polymerase measured in isolated nuclei is increased. The concentration of NAD+ in cardiac muscle increases during postnatal development. In the adult compared with the 1-day-old neonatal rat the concentration of NAD+ relative to fresh tissue weight, DNA or protein increased 1.7-fold, 5.2-fold or 1.4-fold respectively. The concentration of NAD+ in cardiac muscle of the 1-day-old neonatal rat can be increased by approx. 20% by dibutyryl cyclic AMP. These data suggest that NAD+ and poly(ADP-ribose) polymerase may be involved with the repression of DNA synthesis and cell proliferation in differentiating cardiac muscle.
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PMID:Poly(adenosine diphosphate ribose) polymerase activity and nicotinamide adenine dinucleotide in differentiating cardiac muscle. 18 Sep 77

Deoxythymidine kinases (EC 2.7.1.--) induced in HeLa TK- cells by Herpes simplex Type I and Type II viruses both had a requirement for divalent cations. The enzymes had the highest activities in the presence of Mg2+, followed by Mn2+, Ca2+, Fe2+, and in that order, whereas they were inactive in the presence of Zn2+ and Cu2+. The amount of Mg2+ required for optimal activity was dependent on the amount of ATP present, so that optimal activities were found when the concentration of Mg2+ was equal to that of ATP; an excess of Mg2+ inhibited the reaction. The activities of various nucleoside triphosphates as phosphate donors for Herpes simplex virus Type I deoxythymidine kinase were in the order: ATP = dATP = ara ATP greater than CTP greater than dCTP greater than UTP greater than dUTP greater than GTP greater than dGTP. Those for Herpes simplex virus Type II deoxythymidine kinase were in the order: CTP greater than dCTP = ara CTP greater than dATP greater than ATP greater than UTP greater than GTP greater than dUTP = dGTP. For both deoxythymidine kinases induced by Herpes simplex virus, the nucleoside triphosphates tested exerted cooperative effects. The Km values of ATP and CTP for the Herpes simplex virus Type I enzyme were 30 and 70 muM respectively; whereas those for the Herpes simplex virus Typr II enzyme were 140 and 450 muM. Studies on binding of various thymidine analogs with free 5'-OH to these deoxythymidine kinases indicated that 5-substituted ethyl-, vinyl-, allyl-, propyl-, iodo- and bromo-dUrd as well as iodo5 dCyd and bromo5 dCyd had good affinity to both enzymes. In contrast, vinyl5 Urd, iodo5 Urd and arabinosylthymidine had good affinity only to the Herpes simplex virus Type I enzyme but not to the Herpes simplex virus Type II deoxythymidine kinase. All of these thymidine analogs were competitive inhibitors, with KI values in the range of 0.25 to 1.5 muM. Herpes simplex virus Type I deoxythymidine kinase was less sensitive to either dTTP or iodo dUTP inhibition than Herpes simplex virus Type II. Both dThd and dCyd could serve as substrates and competed with each other for Herpes simplex viruses Type I and Type II induced kinases, but they differed in their Km values for these enzymes. The Km values of dThd and dCyd were 0.59 muM and 25 muM for Herpes simplex virus Type I deoxythymidine kinase; while they were 0.36 muM and 88 muM respectively for the Herpes simplex virus Type II enzyme.
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PMID:Deoxythymidine kinase induced in the HELA TK- cells by herpes simplex virus type I and type II. Substrate specificity and kinetic behavior. 18 65

Herpes simplex virus type 1 (HSV-1) encoded thymidine kinase converts 5-iodo-5'-amino-2',5'-dideoxyuridine (AIdUrd), a highly specific anti-herpes agent, into the 5'-diphosphate (AIdUDP) derivative in vitro. AIdUDP was identified by its acid lability, sensitivity to alkaline phosphatase hydrolysis, chromatographic behavior, and ratio of double isotope (125I, 32P) labeling. ATP, but not AMP, is a phosphate donor, and the direct transfer of the beta and gamma phosphate of ATP as pyrophosphate to AIdUrd was ruled out. The presence of a phosphoramidate bond was supported by the acid lability of AIdUDP which has a half life (t1/2) of 320 min at pH 3.0. At neutral pH, the hydrolysis products are AIdUrd and orthophosphate, with AIdUrd monophosphate being the probable hydrolytic intermediate at these pH values. However, at acidic pH, some pyrophosphate was detected in addition to AIdUrd and orthophosphate. AIdUrd competitively inhibited the phosphorylation of thymidine and deoxycytidine. Escherichia coli thymidine kinase, even though 100-fold higher in activity, was unable to phosphorylate AId-Urd under similar incubation conditions.
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PMID:Phosphorylation of 5-iodo-5'-amino-2',5',dideoxyuridine by herpes simplex virus type 1 encoded thymidine kinase. 22 42

L5178Y mouse lymphoma cells normally appear to possess two functional thymidine kinase alleles (TK+/+). TK-deficient (TK-/-) clonal lines can be derived from these cells by treatment with EMS or other mutagens. Mezger-Freed [12] has argued that such stable phenotypic variants do not arise as the result of gene mutations but instead represent epigenetic events such as normally occur during differentiation without any permanent gene alteration. If this be so, then rare TK+/- revertants arising in TK-/- cultures should possess TK enzyme identical with one of those present in the original TK+/+ cells, since only depression of the TK gene is involved. Our studies show that this is not the case. Among the mutant TK enzymes analyzed in vitro (those from parental TK+/- lines, each derived in turn from separate TK-/- lines) differences were found in (1) solubility in saline; (2) solubility in 3 M LiCl; (3) Km's; and (4) ATP-Mg2+ requirements. These findings were incompatible with a non-mutational model for the production of these stable variants and, in conjunction with reversion-rate data, they tended to favor either direct structural gene modifications or mutations affecting the expression of adult and fetal enzymes.
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PMID:Evidence for chemically-induced structural gene mutations at the thymidine kinase locus in cultured L5178Y mouse lymphoma cells. 89 58

Thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21) activity increased approx. 200-fold during transformation of human lymphocytes with phytohaemagglutinin. Two peaks of thymidine kinase (peak IS and peak IIS) were separated from stimulated lymphocytes on DEAE-Sephadex. The activity in peak IS was 20-fold the activity in peak IIS. Only one peak was obtained from normal lymphocytes (peak IIN). The elution volume of this peak was identical to that of peak IIS. The Km values for ATP were 1 mM for peak IS, 0.2 mM for peak IIS and 0.3 mM for peak IIN. 90 micronM dTTP gave 50% inhibition of the activity in peak IS, while the same inhibition of the activities in peak IIS and peak IIN was obtained with only 15 micronM dTTP. Km for thymidine was about 6 micronM for peak IS. The kinetic relation between thymidine and the activity in peak IIS was complex but very similar to that of peak IIN. It is suggested, that a new form of thymidine kinase appears in the lymphocytes due to phytohaemagglutinin stimulation.
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PMID:Induction of thymidine kinases in phytohaemagglutinin-stimulated human lymphocytes. 91 39

Treatment with methylglyoxal bis(guanylhydrazone), a specific inhibitor of S-adenosylmethionine decarboxylase (EC 4.1.1.50), suppressed the phytohemagglutinin-induction of [3H]thymidine uptake by guinea pig lymphocytes. The kinetics of [3H]thymidine uptake revealed that the Km value for thymidine was not changed, but the V value was markedly lowered by the methylglyoxal bis(guanylhydrazone) treatment. The induction of ATP: thymidine 5'-phosphotransferase (EC 2.7.1.75) (thymidine kinase) activity by phytohemagglutinin was suppressed to about the same extent as the induction of thymidine uptake. These suppressions were dependent on the methylglyoxal bis(guanylhydrazone) doses and on duration of the methylglyoxal bis(guanylhydrazone) treatment. Analysis of [3H]thymidine labelled compounds of the acid-soluble fraction showed that conversion of thymidine to thymidine 5'-triphosphate was inhibited by the methylglyoxal bis(guanylhydrazone) treatment. DNA polymerase activity was less inhibited by the methylglyoxal bis(guanylhydrazone) treatment in comparison with the methylglyoxal bis(guanylhydrazone) inhibition of thymidine uptake by whole cells. These results strongly suggested that blocking of polyamine accumulation by the methylglyoxal bis(guanylhydrazone) treatment influenced phytohemagglutinin induction of thymidine phosphorylation, resulting in a decrease of thymidine incorporation into DNA.
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PMID:Suppression of phytohemagglutinin-induction of thymidine uptake in guinea pig lymphocytes by methylglyoxal bis(guanylhydrazone) treatment. 91 40

The activities of two deoxythymidine-phosphorylating enzymes--thymidine kinase and nucleoside phosphotransferase--were found in the cytoplasmic fraction of normal and regenerating rat liver. The specific activity of nucleoside phosphotransferase appeared to be by 50% higher than that of thymidine kinase. Nucleoside phosphotransferase has a broad specificity for the phosphate donor. This enzyme is more stable to heating and prolonged dialysis as compared to thymidine kinase. The enzymes respond differently to the addition of d-TTP, d-CTP and sturins A and B: thymidine kinase is strongly inhibited by these agents whereas nucleoside phosphotransferase is insensitive to d-TTP and d-CTP and is only slightly inhibited by sturins. On the other hand the activity of nucleoside phosphotransferase is considerably decreased after addition of ATP. Changes in the activities of both enzymes during 50 hrs following partial hepatectomy were studied. Two activity maxima were observed at 20-22 and 40-46 hrs of regeneration. Using polyacrylamide gel electrophoresis, three isoforms of both enzymes were found. The ratio between the isoenzyme content of the two enzymes from the cytoplasmic fraction of regenerating liver varied as compared to normal.
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PMID:[Some properties of cytoplasmic thymidine kinase and nucleoside phosphotransferase from rat liver]. 91 49

Enzymes of DNA synthesis, thymidine kinase (ATP-thymidine-5'-phospho-transferase, EC 2.7.1.21), DNA polymerase (EC 2.7.7.7) and nuclease activities were investigated in isolated purified nuclei of swine aorta. Thymidine kinase which is detectable in these nuclei can be stimulated by the addition of phospholipase C. DNA polymerase activity of isolated nuclei is strongly dependent on addition of an exogenous template; the preferred template is activated DNA. The activity in the absence of an added template is very low except when labelled dCTP is used as the precursor. This incorporation of labelled dCTP does not require the addition of the other three triphosphates, and under these conditions, dCTP seems to be incorporated into what may be a homopolymer. As with other tissues, solubilized preparations of aortic nuclei have two DNA polymerase activities which also prefer activated DNA template. There is no detectable endonuclease in aortic nuclei.
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PMID:Enzymes of DNA synthesis in isolated nuclei of swin aorta. 94 21


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