Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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 metabolism of [2-14C]thymine and [2-14C]thymidine in the cotyledons and embryonic axes of black gram (Phaseolus mungo) seedlings was investigated. Both [2-14C]thymine and [2-14C]thymidine degraded extensively into [14C]CO2. The rate of release of [14C]CO2 from [2-14C]thymine was much greater than that from [2-14C]thymidine. Radioactivity from both precursors was also observed beta-ureidoisobutyric acid. This indicated that thymine was degraded by the reductive pathway of pyrimidine degradation. Small amounts of [2-14C]thymine and [2-14C]thymidine were salvaged for deoxyribonucleotide and DNA synthesis. The highest incorporation of [2-14C]thymine and [2-14C]thymidine into the DNA fraction was observed in 24 hour-old cotyledons where net DNA synthesis was not observed. These precursors seem to be utilised for DNA synthesis of organelles of the cotyledonary cells, probably mitochondria. In embronic axes, [2-14C]thymine is more effectively salvaged for DNA synthesis than [2-14C]thymine. The incorporation rate increased during the early phase of germination and attained its maximum at 48 h after which it decreased. No thymidine kinase activity was detected in either cotyledons or in the embryonic axes. Thymidine salvage seems to be catalysed by nucleoside phosphotransferase which is present both in the cotyledons and in the embryonic axes. This suggests that, in contrast to other pyrimidine and purine bases and nucleosides, no specific salvage system for thymine and thymidine is present in black gram seedlings.
 ...
PMID:[Metabolism of [2-14C]thymine and [2-14C]thymidine in germinating black gram (Phaseolus mungo) seeds]. 241 Sep 55

Carbetimer, an intermediate molecular-weight-derivatized copolymer of maleic anhydride and ethylene, has been shown to possess significant antineoplastic activity in the stem cell assay. We have examined the antitumor activity of carbetimer in vivo and in vitro against HM5-Carb/S and M21, both primary human melanoma cell lines sensitive and resistant to carbetimer, respectively. The mechanism of action of carbetimer in HM5-Carb/S has been determined. Mice bearing palpable sensitive tumors were treated with 10% lethal doses of carbetimer (1500 mg/kg i.p.). The tumor nucleotide profile was determined 4 hours later. Uridine and cytidine nucleoside triphosphates were reduced by 36.6 and 58.2%, respectively. In a similar experiment using carbetimer-resistant tumor, there was no change in the tumor pool sizes of uridine and cytidine nucleoside triphosphate pools in carbetimer- or saline-treated animals. Following 24-h exposure of the cells to 1000 microM concentration of carbetimer, the carbetimer-sensitive cells were pulsed with [14C]uridine, cytidine, or thymidine for 30 min. Pyrimidine nucleotides, in particular triphosphates, were reduced significantly as compared to the saline-treated control. Similar treatment of carbetimer-resistant cells resulted in no change in the pool sizes of the nucleotides. [14C]Bicarbonate flux studies demonstrated that [14C]CO2 conversion into UMP and CMP was increased 200 and 140% of control in the carbetimer-sensitive cells treated with 1000 microM carbetimer; however, a similar treatment of the resistant cells showed no change in the pool sizes of the nucleotide. Examination of pyrimidine salvage enzymes demonstrated that, in the sensitive cells, carbetimer treatment reduced the specific activity of uridine, cytidine, and thymidine kinase by 46, 37, and 60%. In a similar study using resistant cells, the specific activities were reduced 7 and 0%, respectively. In the restitution studies coincubation of carbetimer-sensitive cells with carbetimer and uridine resulted in essentially the reversal of carbetimer cytotoxicity. Thus, carbetimer inhibits the growth of the sensitive cells by inhibiting the uptake and metabolism of performed nucleosides both in vivo and in vitro.
 ...
PMID:Mechanism of action of a new antitumor agent, carbetimer. 375 94

We investigated the effects of hypoxia (< 2.5% O2) on rat manganese superoxide dismutase (MnSOD) gene promoter-luciferase reporter constructs in transiently transfected lung epithelial cells (A549, L2, and E1A-T2) and fibroblasts (R9Ab). We cloned MnSOD promoter-luciferase reporter constructs (numbers refer to length in base pairs [bp] in the 5' direction from the transcription initiation site): 2,505, 1,064, 507, 405, and 289 into pGL2-Basic, a promoterless, firefly luciferase vector. Lung cells were transfected with MnSOD promoter-reporter constructs with or without thymidine kinase-driven Renilla luciferase (pRL-TK), and were exposed to air/5% CO2 or hypoxia (2.5% O2/5% CO2/balance N2) for 24 h. Hypoxia caused a significant (by two-way analysis of variance) consistent increase in luciferase in the A549 cell (human lung carcinoma) line. Greatest expression (> 3-fold increase) in hypoxia was associated with the 2,505-bp MnSOD promoter (normalized to cellular protein). Azide (10 microM) did not increase expression of the MnSOD reporter constructs. The 289-bp promoter was sufficient to express the reporter in air and to increase its expression in hypoxia. Promoter activity of the rat MnSOD 5' region, assessed by luciferase reporter constructs in A549 cells, increased in hypoxia. The increase was exclusive to A549 cells and did not occur in other cells.
 ...
PMID:Hypoxic modulation of manganese superoxide dismutase promoter activity and gene expression in lung epithelial cells. 1038