Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An endonuclease, present in the microplasmodia of Physarum polycephalum, has been partially purified from isolated nuclei by DEAE-cellulose and Sephadex G-75 chromatography. 1. The endonuclease produced single-strand scissions in double-stranded DNA which resulted in the generation of 5'-phosphoryl and 3'-hydroxyl termini. No activity was observed with single-stranded DNA as substrate. 2. The pH optimum was approximately 8.5. 3. Divalent cations were essential for enzyme activity. MnCl2 and MgCl2 gave maximal activity. CaCl2, ZnCl2 or CoCl2 did not activate the enzyme. 4. The endonuclease activity was highly sensitive to monovalent cations. 5. Endonuclease activity was found in two forms after gel filtration: an activity in a homogeneous peak with a molecular weight of approx. 20 000, and an activity that had a heterogeneous molecular weight and which was isolated in a complex with DNA. A possible function of the endonuclease in DNA replication is discussed.
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PMID:Endonuclease activity in nuclei of Physarum polycephalum. Partial purification and characterization. 2 Jan 46

Escherichia coli endonuclease IV and its Saccharomyces cerevisiae homologue Apn1, two DNA repair enzymes for free radical damages, were previously shown to be inactivated by metal-chelating agents. In the present study, atomic absorption spectrometry of endonuclease IV revealed the presence of 2.4 zinc and 0.7 manganese atoms, whereas Apn1 contained 3.3 zinc atoms and no significant manganese. EDTA-inactivated endonuclease IV retained 0.7 zinc atom but little detectable manganese. ZnCl2 reactivated 1,10-phenanthroline-treated Apn1, but was ineffective with endonuclease IV treated with either 1,10-phenanthroline or EDTA. In contrast, enzymatic activity was restored to both enzymes after EDTA treatment by incubation with CoCl2 and to a lesser extent by MnCl2. Endonuclease IV, reactivated with CoCl2 or MnCl2, regained all of the activities characteristic of the native enzyme. MnCl2 was as effective as CoCl2 at restoring activity to the 1,10-phenanthroline-treated enzymes. The results indicate that intrinsic metals play critical roles in both endonuclease IV and Apn1 and that manganese may perform a special function in endonuclease IV. Possible mechanistic roles for the metals in these DNA repair enzymes are discussed.
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PMID:Metalloenzymes in DNA repair. Escherichia coli endonuclease IV and Saccharomyces cerevisiae Apn1. 172 Jul 75

An endonuclease endogenous to rat-liver nuclei has been purified by a series of chromatographic procedures and finally by isoelectric focusing (IEF) electrophoresis. The nuclease fraction prepared by the IEF electrophoresis (IEF fraction) showed a pI value of 5.7 and migrated as a single band to a molecular weight position of 46,000 on an SDS-polyacrylamide gel. The activity for single-stranded DNA was enhanced by 10 mM MgCl2 and/or by 5-15 mM MgCl2 in the presence of 2 mM CaCl2 (an optimum pH, 7.0), but was lowered by CaCl2 alone and inhibited strongly by ZnCl2 or MnCl2. The activity for duplex DNA was rather low, although an optimum condition was 10 mM MgCl2. In fact, even under this condition, the activity was about 40% lower than that for single-stranded DNA. Moreover, the IEF fraction formed single-strand nicks much more rapidly than double-strand cuts in pBR322 DNA, and preferentially produced deoxyadenosine 5'-monophosphate termini in the DNA. In addition, RNAase activity was also detected in this fraction.
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PMID:Purification and properties of an endonuclease endogenous to rat-liver nuclei. 254 36

Cell death via apoptosis is an important event involved in a number of immunological processes. Recently, apoptosis has been associated with oxidative stress in a number of cell systems. Here we assessed the inhibitory capacity of different antioxidants on UV- and drug-induced apoptosis in the human leukemic cell line, HL-60. We found that the oxygen radical scavenger, BHA, the radioprotector cysteamine and the metal chelators, pyrrolidinedithiocarbamate (PDTC), diethyldithiocarbamate (DEDTC), and dimethyldithiocarbamate (DMDTC), were able to significantly inhibit nuclear fragmentation and reduce the formation of apoptotic bodies in UV-irradiated human leukemic cells. Both BHA and PDTC were found to reduce DNA fragmentation as assessed by in situ DNA nick-end labelling and quantification thereof using fluorescence flow cytometry. In addition to inhibiting UV-induced apoptosis, PDTC was also capable of reducing the amount of apoptosis induced by a range of cytotoxic drugs, such as actinomycin-D, camptothecin, etoposide, and melphalan, whereas BHA and cysteamine were not as effective in these cases after more than four hours in culture when compared to PDTC. To further elucidate the working mechanism of PDTC, we have looked at the effect of PDTC on DNA fragmentation in isolated nuclei, under conditions that promote activation of endogenous endonuclease involved in apoptosis. In contrast to ZnCl2, a potent inhibitor of endonuclease activity, PDTC was unable to inhibit DNA-ladder formation in this assay. Taken together, these results indicate that oxygen radicals may have a central role to play in the induction of apoptosis and that dithiocarbamates can serve as potent inhibitors of apoptosis induced by a wide variety of stimuli.
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PMID:Inhibition of apoptosis by antioxidants in the human HL-60 leukemia cell line. 757 57

A low concentration of bufalin, a component of bufadienoides in the traditional Chinese medicine chan'su, was shown previously to induce differentiation of a broad range of human leukemia cell lines. In the present study, we found that bufalin at concentrations of 10(-7) M and higher induced apoptosis in human leukemia cells, such as HL60, ML1, but not in mouse leukemia M1 cells. A mere 15 min pretreatment of HL60 cells with 10(-6) M bufalin, followed by incubation for 15 h without bufalin, caused fragmentation of DNA and a decrease in cell viability, indicating that the signal for induction of apoptosis is triggered rapidly upon treatment with bufalin. Bufalin-induced apoptosis in HL60 cells was inhibited by ZnCl2, an inhibitor of endonuclease, but not by cycloheximide, an inhibitor of protein synthesis. Northern blot analysis revealed that the levels of expression of the c-myc and bcl-2 genes in HL60 cells decreased with time after treatment with bufalin. These results suggest that bufalin induces apoptosis specifically in human leukemia cells by altering the expression of these genes involved in apoptosis.
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PMID:Bufalin induces apoptosis and influences the expression of apoptosis-related genes in human leukemia cells. 765 1

A common strongly ordered multi-step-pattern of endogenous DNA degradation was induced in rat liver nuclei and intact thymocytes, prepared in the presence of chelating agents and incubated in the presence of CaCl2 and/or MgCl2. It consisted of sequential generation of 0.3 Mbp, then 0.05 Mbp DNA fragments and finally of oligo- and mononucleosomal DNA. Oligonucleosomal DNA was generated when the genome had already been disintegrated into 0.05 Mbp DNA fragments. ZnCl2 completely inhibited advanced genome cleavage to oligo- and mononucleosomal DNA without affecting the initial generation of large DNA fragments. Therefore, the endonucleolytic activity which produce large DNA fragments is different from Ca2+/Mg2+ endonuclease. The similar pattern of DNA degradation was observed in thymocytes treated with dexamethasone and with the topoisomerase II inhibitor VM-26, the agents known to induce apoptosis. The effect of VM-26 strongly suggests the involvement of topoisomerase II in generation of large DNA fragments. Multi-level organization and regulation of the chromatin structure determine the stepwise process of genome degradation. Detachment of chromatin from the nuclear matrix attachment regions may be one of the possible mechanisms of switching off the genome function and triggering the multi-step process of endogenous chromatin degradation thus leading to cell death in terminal differentiation or stress-induced apoptosis.
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PMID:Comparative study of induction of endogenous DNA degradation in rat liver nuclei and intact thymocytes. 774 35

The src-related protein tyrosine kinase p56lck is thought to be important in regulating maturation and functional responsiveness of T cells and thymocytes. In the present studies we report that expression of p56lck is suppressed during apoptosis. Using primary cultures of rat thymocytes, we found that agents that are effective in inducing apoptosis, including okadaic acid, dexamethasone, and antibodies to the CD3 receptor, also deplete cells of p56lck. This process is rapid, occurring within 24 h, and is not due to cytotoxicity. Inhibition of DNA fragmentation in apoptotic cells with the endonuclease inhibitor ZnCl2 failed to prevent depletion of p56lck, suggesting that it was not a consequence of the DNA degradation process. Using the thymic lymphoma cell line LSTRA, apoptosis was also associated with cellular depletion of p56lck. In contrast to thymocytes, this process required 48-72 h possibly because these cells overexpress p56lck. Although at this time we are uncertain as to the precise role of p56lck in the process of apoptosis, our results indicate that changes in the expression of this protein in thymocytes is an important marker of programmed cell death.
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PMID:Cellular depletion of p56lck during thymocyte apoptosis. 793 Sep 51

Apoptosis is the predominant form of cell death observed in a variety of physiological and pathological conditions such as cancer involution, insect metamorphosis, the development of the immune and nervous systems, and embryogenesis. The typical nuclear changes taking place in apoptotic cells include extensive condensation of chromatin and internucleosomal DNA fragmentation into units of 200 base pairs. However, the mechanisms responsible for both chromatin condensation and DNA fragmentation have yet to be elucidated. In this study, micrococcal nuclease and the divalent cations, Ca2+ and Mg2+, were applied to isolated nuclei in an attempt to reconstitute in vitro the digestion of genomic DNA associated with apoptosis. Micrococcal nuclease was found to induce a typical pattern of DNA fragmentation, but did not give rise to chromatin condensation, whereas Ca2+/Mg2+ induced both chromatin condensation and DNA fragmentation in isolated mouse liver nuclei. When the endonuclease inhibitor ZnCl2 was used, the DNA fragmentation induced by Ca2+/Mg2+ in nuclei could be completely inhibited, but chromatin condensation still occurred. For comparison, intact liver cells were treated with valinomycin, a potassium ionophore, which gave rise to an atypical cell death, with chromatin condensation appearing without DNA fragmentation. Our results suggest that endonuclease activation in apoptosis is neither necessary nor sufficient to induce chromatin condensation, and that DNA fragmentation and chromatin condensation may be triggered through separate pathways during apoptosis.
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PMID:Separate metabolic pathways leading to DNA fragmentation and apoptotic chromatin condensation. 829 67

Activation of immature thymocytes or transformed T lymphocytes via T-cell receptor (TCR)/CD3 signalling can induce programmed cell death (apoptosis). Recent data indicate that anti-CD3/TCR monoclonal antibodies (mAb) also trigger apoptosis in activated (but not resting) mature peripheral blood T lymphocytes. Here we report that triggering of resting CD4-CD8-TCR alpha beta+ and/or TCR gamma delta+ via the alternative CD2-dependent activation pathway is able to induce programmed cell death. A pair of mitogenic anti-CD2 mAb provoked a dramatic rise in [Ca2+]i that was almost entirely sustained by extracellular fluxes, and the inhibition of membrane [Ca2+/Mg2+] ATPase. The resulting endonuclease activation was able to induce DNA fragmentation, as revealed by propidium iodide staining and gel electrophoresis. Induction of apoptosis was prevented by the presence of interleukin-4 (IL-4) as well as by endonuclease inactivation with 100 microM ZnCl2, but enhanced by the contemporary block of protein kinase C. Thus it seems that in resting T lymphocytes the strong calcium signal delivered by the alternative CD2 activation pathway may act as a negative apoptotic signal in both alpha beta and gamma delta T cells with low (non-major histocompatibility complex restricted) antigenic affinity, so limiting the extension of polyclonal T-cell growth.
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PMID:IL-4 is able to reverse the CD2-mediated negative apoptotic signal to CD4-CD8- alpha beta and/or gamma delta T lymphocytes. 855 74

Recently we have reported that T-2 toxin, a trichothecene mycotoxin produced by Fusarium species, is a potent inducer of apoptosis in the human promyelotic cell line HL-60. To clarify the signal transduction pathway of apoptosis primed by T-2 toxin, T-2 toxin-induced apoptosis was investigated in detail using confocal laser microscopy and flow cytometry. Apoptosis in HL-60 cells induced by T-2 toxin was dose dependent when the cells were treated with concentrations of 5-100 ng/ml for more than 2 hr. The apoptosis proceeds through various cell cycle stages of HL-60 cells. Prior to apoptosis, the intracellular calcium ion (Ca+2i) level was markedly elevated within 3-5 min after exposure to T-2 toxin and returned to normal level thereafter. A well-known chelator for Ca+2i, ethylene-N,N,N', N'-tetraacetic acid 4K acetoxymethyl ester (BAPTA-AM), a Ca+2-dependent endonuclease inhibitor ZnCl2, and calpain inhibitor 1 sharply blocked T-2 toxin-induced apoptosis. These results strongly suggest that the Ca+2 signal triggered by T-2 toxin is transduced by the activation of endonuclease and protease, and ultimately evokes apoptosis.
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PMID:Transient elevation of intracellular calcium ion levels as an early event in T-2 toxin-induced apoptosis in human promyelotic cell line HL-60. 894 99


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