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)

In an attempt to differentiate between thymidine kinase (EC.2.4.1.21) induced by herpesvirus hominis type I (TK I) and type 2 (TK2), the different susceptibilities to the modifying effects of some thymidine analogues proved to be useful criteria: (I)2'-deoxythymidine-5'-triphosphate (dThd-5'-PPP) inhibits TK 2 at a concentration of 0-125 mM by 90%, whereas TK I is inhibited at 4-03 mM by 50%. (2) 2'-deoxythymidine-5'-monophosphate (dThd-5'-P) competitively inhibits TK 2 at all concentrations tested. On the other hand, the direction of its effect on TK I is concentration dependent: at 500 mum it stimulates and at 8 mM inhibits TK I activity. During enzyme kinetic studies, TK I displays substrate inhibition which is reversed by dThd-5'-P. This result explains the stimulating effect of dThd-5'-P at 500 muM. This phenomenon suggests the existence on the enzyme molecule of a second binding site for dThd which mediates substrate inhibition and which can be occupied also by dThd-5'-P. After polyacrylamide gel electrophoresis of TK I, the stimulation by dThd-5'-P disappears, suggesting the separation of the second binding site from the catalytic centre.
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PMID:Regulation by thymidine monophosphate and other nucleotides of thymidine kinase activity in extracts from primary rabbit kidney cells infected by HSV types 1 and 2. 17 38

Human cells salvage pyrimidine deoxyribonucleosides via 5'-phosphorylation which is also the route of activation of many chemotherapeutically used nucleoside analogs. Key enzymes in this metabolism are the cytosolic thymidine kinase (TK1), the mitochondrial thymidine kinase (TK2) and the cytosolic deoxycytidine kinase (dCK). These enzymes are expressed differently in different tissues and cell cycle phases, and they display overlapping substrate specificities. Thymidine is phosphorylated by both thymidine kinases, and deoxycytidine is phosphorylated by both dCK and TK2. The enzymes also phosphorylate nucleoside analogs with very different efficiencies. Here we present specific radiochemical assays for the three kinase activities utilizing analogs as substrates that are by more than 90 percent phosphorylated solely by one of the kinases; i.e. 3'-azido-2',3'-dideoxythymidine (AZT) as substrate for TK1, 1-beta-D-arabinofuranosylthymidine (AraT) for TK2 and 2-chlorodeoxyadenosine (CdA) for dCK. We determined the fraction of the total deoxycytidine and thymidine phosphorylating activity that was provided by each of the three enzymes in different human cells and tissues, such as resting and proliferating lymphocytes, lymphocytic cells of leukemia patients (chronic lymphocytic, chronic myeloic and hairy cell leukemia), muscle, brain and gastrointestinal tissue. The detailed knowledge of the pyrimidine deoxyribonucleoside kinase activities and substrate specificities are of importance for studies on chemotherapeutically active nucleoside analogs, and the assays and data presented here should be valuable tools in that research.
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PMID:Selective assays for thymidine kinase 1 and 2 and deoxycytidine kinase and their activities in extracts from human cells and tissues. 135 86

Three key enzymes in the anabolic phosphorylation of deoxyribonucleosides and deoxyribonucleoside analogs were purified i.e. cytoplasmic thymidine kinase (TK1), mitochondrial thymidine kinase (TK2) and cytoplasmic deoxycytidine kinase (dCK) from human, mouse and monkey liver and spleen. Their subunit structure and substrate specificities were compared. Extensive purification of TK1 and dCK from mouse spleen and TK2 from mouse and monkey livers revealed major polypeptide bands of 25, 30 and 28 kD, respectively, on sodium dodecyl sulphate-polyacrylamide gel electrophoresis which are very similar to the subunit molecular weights of the corresponding human enzymes. Affinity purified polyclonal antibodies against human dCK also cross-reacted with 30 kD bands in extracts from both mouse and monkey spleen. Thus, the molecular weights of the subunits of these three enzymes appeared to be very similar in all three species. TK1 and TK2 from these different sources appeared to have similar substrate specificities against several deoxyribonucleoside analogs. However, mouse dCK differed significantly from monkey and human dCK in its capacity to phosphorylate dAdo and 2',3'-dideoxycytidine (ddCyd) with a Vmax approximately 10-fold lower than that of the two latter enzymes. The Km and Vmax values for dCyd and arabinocytosine appeared to be very similar with the enzymes from all three species. The fact that mouse dCK shows low activity with dAdo and ddCyd explains differences reported previously in the metabolism of dAdo and ddCyd in mouse compared to that in human lymphocytes. These results argue against the use of mice as model systems for human deoxynucleoside metabolism.
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PMID:Deoxynucleoside phosphorylating enzymes in monkey and human tissues show great similarities, while mouse deoxycytidine kinase has a different substrate specificity. 165 2

Deoxynucleoside kinases are required for the 5'-phosphorylation of deoxynucleoside analogs used in chemotherapy. Cytoplasmic thymidine kinase (TK1), deoxycytidine kinase (dCK) and mitochondrial thymidine kinase (TK2) were completely purified from human leukemic spleen and their capacities to phosphorylate 43 nucleoside analogs were compared. TK1 showed the most restricted substrate specificity but tolerated 3'-modifications of the sugar ring and some 5-substitutions of the pyrimidine ring. TK2 showed a much broader specificity and phosphorylated pyrimidine bases with bulky 5-substitutions, including cytosine analogs, while sugar analogs with substituents other than OH in the 2' and 3' positions were very poor substrates. dCK showed a very broad specificity phosphorylating several cytosine analogs with 2' and 3' modifications as well as acyclic sugar analogs. Purine deoxyribonucleosides were also efficiently phosphorylated by dCK but in this case sugar modifications led to drastically decreased activity.
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PMID:Comparison of the substrate specificities of human thymidine kinase 1 and 2 and deoxycytidine kinase toward antiviral and cytostatic nucleoside analogs. 202 74

Three isoenzymes of thymidine kinase (TK) identified on Ehrlich ascites tumour corresponding to pl values of 5.3, and 6.9 and 8.3 were studied with respect to their kinetic properties. The isoenzymes were separated by thin-layer isoelectric focusing and measured in the presence of thymidine (TdR) as substrate, adenosinetriphosphate (ATP) as phosphor donor and deoxythymidinetriphosphate (dTTP) as inhibitor. Exponentially growing cells and growth inhibited cells were used with high proportions of the isoenzymes at pl values of 6.9 and 8.3, and 5.3 respectively. The concentrations of the former were further enhanced by the use of S-phase cells isolated by elutriator centrifugation. The isoenzymes were identified as TK1-onc, earlier found in human leukemia cells. In order to confirm the existence of TK1, particular at pl value 5.3, the ability of the isoenzymes to use different phosphor donors (ATP and uridinetriphosphate (UTP)) and substrates (TdR and deoxycytidine (dCdR) was also studied. These results showed that the isoenzymes at pl 6.9 and 8.3 correspond to TK1, while the isoenzyme at pl 5.3 is heterogeneous. Further, high resolution isoelectric focusing confirmed the existence of two isoenzymes at pl values of 5.1 and 5.3, representing mitochondrial (TK2) and cytoplasmic (TK1) isoenzymes.
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PMID:Enzyme kinetics of thymidine kinase isoenzymes of Ehrlich ascites tumour. 224 Nov 1

Levels of the nucleotide pathway enzyme thymidine kinase (TK) were assayed in the mononuclear leukocytes and serum of 70 female patients with breast cancer and 98 male and 77 female non-cancer hospital patients. The total TK levels in both mononuclear leukocytes and serum from patients with breast cancer were significantly higher than in controls. The serum TK levels showed a significant correlation with cancer stage. No such correlation was observed with mononuclear leukocyte TK levels. Serum TK from 20 patients with breast cancer and 19 control patients was further assayed to ascertain the relative contributions of the thymidine kinase isozymes TK1 and TK2 to total TK levels. The increase in serum TK from breast cancer patients appears to be due to an increase in both TK1 and TK2 levels.
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PMID:Thymidine kinase activities in mononuclear leukocytes and serum from breast cancer patients. 340 46

The activity of thymidine kinase (TK) and the proportion of its isozymes (TK1/TK2) were studied in peripheral lymphoid cells of 37 children with acute lymphocytic leukemia (ALL). The high TK in 25 untreated subjects (31.5 +/- 8.9) decreased during chemotherapy-induced remission to uniformly low (5.3 +/- 0.4) normal values, and rose again during relapse to a mean of (24.8 +/- 8.1). The proportion of isozyme 1 followed the same pattern but TK was a more sensitive indicator of disease state. The lymphocyte fractions' TK (per mg protein) correlated with the number (per ml blood) of WBCs, blasts and lymphocytes. Although the higher TK of blasts than of apparently normal lymphocytes was confirmed in cases permitting clean physical separation, the lymphocyte fraction of several untreated subjects with minimal blast counts also exhibited elevated TK. Moreover, this elevation was also seen in relapsed cases even if their blood (unlike bone marrow) was devoid of blasts. The results indicate that quantification of TK can reveal a subpopulation of maldifferentiated lymphocytes which are microscopically normal and that it may provide an objective parameter of prognostic differences between ALL subjects with similar hematological characteristics.
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PMID:Lymphocyte thymidine kinase and treatment response in acute lymphocytic leukemia. 346 83

The profile of thymidine kinase isoenzymes was determined in peripheral blood lymphocytes from 14 patients with chronic lymphocytic leukaemia (CLL) and 31 controls. Twelve patients with indolent disease showed TK2 isoenzyme activity, while two patients in whom the disease evolved and two patients who presented with aggressive disease exhibited TK1 isoenzyme activity. The demonstration of TK1 activity in the peripheral blood lymphocytes of clinically aggressive CLL suggests that this isoenzyme may be a useful biochemical marker of such behaviour.
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PMID:Thymidine kinase isoenzymes in chronic lymphocytic leukaemia. 729 90

To determine whether kinase (TK) isozyme status adds clinically useful information in adult non-Hodgkin's lymphoma (NHL), we have analyzed peripheral blood plasma and lymphocytes of 44 patients with NHL for either TK1 or TK2 isozyme activity. On the basis of isozyme status, patients could be divided into two groups that did not differ significantly with respect to known determinants for survival. The median survival of patients exhibiting peripheral blood TK1 thymidine kinase activity was 40 wk and that of individuals with TK2 activity was in excess of 200 wk. These data suggest that peripheral blood TK1 isozyme is a useful independent biochemical marker for a subgroup of NHL who respond poorly to current therapy and thus require new therapeutic approaches.
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PMID:Prognostic relevance of thymidine kinase isozymes in adult non-Hodgkin's lymphoma. 729 3

The activities of thymidine kinase (TK) isoenzyme 1 and 2 were examined in extracts of human benign or malignant lymphoid tissue and correlated with degrees of morphological differentiation. TK2 activity occurred in peripheral blood lymphocytes of normal individuals, patients with chronic lymphocytic leukemia, or solid lymphoid tissue, exhibiting either nonneoplastic histological findings or those of diffuse well-differentiated lymphocytic lymphoma. TK1 activity occurred in solid, non-Hodgkin's lymphoma tissue, exhibiting lesser degrees of cellular differentiation, or in peripheral blood lymphocytes of patients with clinical aggressive chronic lymphocytic leukemia or lymphosarcoma leukemia. In non-Hodgkin's lymphoma tissue, the range of TK1 activities correlated broadly with the Rappaport classification, with higher values occurring in tissue exhibiting changes of diffuse poorly differentiated lymphocytic lymphoma or diffuse histiocytic lymphoma.
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PMID:Thymidine kinase isoenzymes in human malignant lymphoma. 744 15


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